PubMed lets you search millions of journal citations and abstracts in the fields of medicine, nursing, dentistry, veterinary medicine, the health care system, and preclinical sciences. It includes access to ® and to citations for selected articles in life science journals not included in MEDLINE. PubMed also provides access to additional relevant Web sites and links to the other NCBI molecular biology resources.
PubMed is a free resource that is developed and maintained by the National Center for Biotechnology Information (), at the U.S. National Library of Medicine ( ), located at the National Institutes of Health ( ).
Publishers of journals cantheir citations to NCBI and then provide access to the full-text of articles at journal Web sites using .
For a brief overview of searching PubMed, see the Quick Start section.
How can I get the full-text article?
How do I find consumer health information about a disease or condition?
How can I import citations into my reference management program?
How do Ito PubMed?
Why is the link to the full-text not working?
How can I save my search and receive an automatic email update?
How do I search PubMed?
How do I search by author?
How do I search by journal name?
How do I find a specific citation? I have some information such as the author, journal name and the year the article was published.
Is there anything special for clinical searches?
How do I find systematic reviews?
How do I search for medical genetics information?
Can you explain the search results?
How do I display an abstract?
How can I get a copy of the article?
How can I save my results?
I retrieved too many citations. How can I focus my search?
I retrieved too few citations. How can I expand my search?
I’m not finding what I need. How does a PubMed search work?
Is there a guide tofor MEDLINE/PubMed?
I need further assistance and training.
Identify the key concepts for your search.
Enter the terms (or key concepts) in the search box.
Click Go. Click
|What role does pain have in sleep disorders?|
|The key concepts are:|
Enter the author’s last name plus initials without punctuation in the search box and click Go.
If you only know the author’s last name, use the author search field tag [au], e.g., brody[au].
Click the Limits tab to use the author search builder that includes an autocomplete feature.
|A||a, about, again, all, almost, also, although, always, among, an, and, another, any, are, as, at|
|B||be, because, been, before, being, between, both, but, by|
|D||did, do, does, done, due, during|
|E||each, either, enough, especially, etc|
|F||for, found, from, further|
|H||had, has, have, having, here, how, however|
|I||i, if, in, into, is, it, its, itself|
|M||made, mainly, make, may, mg, might, ml, mm, most, mostly, must|
|N||nearly, neither, no, nor|
|O||obtained, of, often, on, our, overall|
|R||rather, really, regarding|
|S||seem, seen, several, should, show, showed, shown, shows, significantly, since, so, some, such|
|T||than, that, the, their, theirs, them, then, there, therefore, these, they, this, those, through, thus, to|
|U||upon, use, used, using|
|W||was, we, were, what, when, which, while, with, within, without, would|
|To search for citations to articles written by Bonnie Ramsey about gene therapy for cystic fibrosis patients enter the following search terms into the search box:|
Full author names may be searched for citations published from 2002 forward if the full author name is available in the article.
Enter the journal name or title abbreviation in the search box.
Add any additional search terms.
Click the Limits tab to use the journal search builder that includes an autocomplete feature.
|To search for citations to articles about drosophila in the journal Molecular Biology of the Cell enter the following in the search box:|
Use the Single Citation Matcher to find citations with a fill-in-the-blank format:
Clickfrom the PubMed sidebar.
Enter the information you have in the fill-in-the-blank boxes.
The Clinical Study Categories use built-in searchthat will limit retrieval to citations to articles reporting research conducted with specific methodologies, including those that report applied clinical research. To find citations for a specific clinical study category:
Clickfrom the PubMed sidebar.
Click Search by Clinical Study Category.
Enter your search terms in the search box.
Select a category: therapy, diagnosis, etiology, or prognosis.
Select a scope: narrow, specific search or broad, sensitive search.
|If you are researching the clinical aspect of gene therapy for cystic fibrosis, from the Clinical Queries page, select the category “therapy” and the Scope “narrow, specific search” and enter the following search terms in the search box:|
In PubMed, Systematic Reviews cover a broad set of articles that build consensus on biomedical topics and Medical Genetics Searches find citations related to topics in medical genetics.
Clickfrom the PubMed sidebar.
Select either Find Systematic Reviews or Medical Genetics Searches.
Enter search terms in the search box.
For Medical Genetics Searches, change the search categories, if applicable.
|If you are researching systematic reviews on inhalation therapy for pneumonia from the Clinical Queries page click Systematic Reviews and enter the following search terms in the search box:|
|To find information on sickle cell anemia and genetic counseling from the Clinical Queries page click Medical Genetic Search, click the All check box to deselect all the categories and click the Genetic Counseling check box. Enter the following search terms in the search box:|
PubMed search results are displayed in a summary format, see the Anatomy of Search Results Page below.
Citations are initially displayed 20 per page with the most recently entered citations displayed first.
You can mouse over a journal’s title abbreviation to display the full journal name.
Click the title of the article to see the abstract. “No abstract available” is indicated on citation’s without an abstract.
PubMed search results do not include an electronic copy of the journal article. However, the abstract display of PubMed citations may provide links to electronic copies from non-PubMed sources, such as directly from the publisher’s Web site.
These electronic journals may require a subscription (which you may access through your local medical library). Sometimes electronic journals have free access. Visit your local medical library if there is not an electronic copy available.
For more information on obtaining the article, see How to Get the Journal Article.
There are several ways to save PubMed search results including using the Clipboard to save citations temporarily and My NCBI Collections to save indefinitely.
Click the check box to the left of the citations you want to save.
From the Send to menu, select Clipboard.
To view your selections, click Clipboard from the Feature tabs.
For other save options, see:
To limit the number of search results:
Replace general search terms with more specific ones (e.g., use low back pain instead of back pain).
Add more search terms.
Use PubMed’s Limits feature to restrict citations by age group, language, publication type, date, human studies, etc.
The tool symbol to the right of the filter tabs links you to My NCBI where you can change your filter selections.
|If the searchretrieves too many citations consider adding more specific search terms to focus your results such as .|
Click the Related Articles link next to a relevant citation. The link displays a pre-calculated set of PubMed citations closely related to the selected article.
Remove extraneous or specific terms from the search box.
Try using alternative terms to describe the concepts you are searching.
|If your search,, retrieves too few citations consider removing search terms to broader the search and retrieve more citations such as, .|
PubMed may modify your search terms to enhance your retrieval. Sometimes these changes may not match what you have in mind.
To see how PubMed modified your search, click Details from the Feature Tabs. You can edit your search in Details.
For additional information, see How PubMed works: Automatic Term Mapping.
|If you search for cystic fibrosis by its abbreviation cf theretrieves some citations that do not discuss cystic fibrosis. To see why PubMed retrieved these citations, click Details to see that PubMed translated cf to search for citations about cerebrospinal fluid or cf.|
E-mail the PubMed
Call the NLM Customer service desk: 1-888-FIND-NLM (1-888-346-3656)
Monday - Friday from 8:30 a.m.-8:45 p.m. EST
Saturday from 9:00 a.m.-5:00 p.m. EST
|Affiliation [AD]Article Identifier [AID]All Fields [ALL]Author [AU]Comment Corrections|
Corporate Author [CN]Create Date [CRDT]EC/RN Number [RN]
Entrez Date [EDAT]
First Author Name [1AU]
Full Author Name [FAU]
Full Investigator Name [FIR]Grant Number [GR]Investigator [IR]
|Issue [IP]Journal Title [TA]Language [LA]Last Author [LASTAU]Location ID [LID]MeSH Date [MHDA]MeSH Major Topic [MAJR]MeSH Subheadings [SH]MeSH Terms [MH]NLM Unique ID [JID]Other Term [OT]OwnerPagination [PG]Personal Name as Subject [PS]Pharmacological Action MeSH Terms [PA]||Place of Publication [PL]|
PMCID & MID
Publication Date [DP]Publication Type [PT]Secondary Source ID [SI]Subset [SB]Substance Name [NM]Text Words [TW]Title [TI]Title/Abstract [TIAB]Transliterated Title [TT]UID [PMID]Volume [VI]
May include the institutional affiliation and address (including e-mail address) of the first author of the article as it appears in the journal. This field can be used to search for work done at specific institutions (e.g., cleveland [ad] AND clinic [ad]).
Includes article identifiers submitted by journal publishers such as doi (digital object identifier). These data are typically used for generating LinkOut links.
Includes all search fields except for Place of Publication and Transliterated Title. Terms enclosed in double quotes or truncated will be searched in all fields. PubMed ignores stopwords.
The format to search for this field is: last name followed by a space and up to the first two initials followed by a space and a suffix abbreviation, if applicable, all without periods or a comma after the last name (e.g., fauci as or o'brien jc jr). Initials and suffixes may be omitted when searching.
PubMed automatically truncates on an author's name to account for varying initials, e.g., o'brien j [au] will retrieve o'brien ja, o'brien jb, o'brien jc jr, as well as o'brien j. To turn off this automatic truncation, enclose the author's name in double quotes and tag with [au] in brackets, e.g., "o'brien j" [au] to retrieve just o'brien j.
|AB||Abstract||English language abstract taken directly from the published article|
|AD||Affiliation||Institutional affiliation and address of the first author|
|AID||Article Identifier||Article ID values supplied by the publisher may include the pii (controlled publisher identifier) or doi (digital object identifier)|
|CI||Copyright Information||Copyright statement provided by the publisher|
|CIN||Comment In||Reference containing a comment about the article|
|CN||Corporate Author||Corporate author or group names with authorship responsibility|
|CON||Comment On||Reference upon which the article comments|
|CRDT||Create Date||The date the citation record was first created|
|CRF||Corrected and republished from||Final, correct version of an article|
|CRI||Corrected and republished in||Original article that was republished in corrected form|
|DA||Date Created||Used for internal processing at NLM|
|DCOM||Date Completed||Used for internal processing at NLM|
|DEP||Date of Electronic Publication||Electronic publication date|
|DP||Publication Date||The date the article was published|
|EDAT||Entrez Date||The date the citation was added to PubMed; the date is set to the publication date if added more than 1 year after the date published|
|EFR||Erratum For||Cites the original article needing the correction|
|EIN||Erratum In||Reference containing a published erratum to the article|
|FAU||Full Author Name||Full Author Names|
|FIR||Full Investigator||Full investigator or collaborator name|
|FPS||Full Personal Name as Subject||Full Personal Name of the subject of the article|
|GN||General Note||Supplemental or descriptive information related to the document|
|GR||Grant Number||Research grant numbers, contract numbers, or both that designate financial support by any agency of the US PHS or Wellcome Trust|
|GS||Gene Symbol||Abbreviated gene names (used 1991 through 1996)|
|IP||Issue||The number of the issue, part, or supplement of the journal in which the article was published|
|IR||Investigator||Investigator or collaborator|
|IRAD||Investigator Affiliation||Affiliation investigator or collaborator|
|IS||ISSN||International Standard Serial Number of the journal|
|JID||NLM Unique ID||Unique journal ID in NLM's catalog of books, journals, and audiovisuals|
|JT||Full Journal Title||Full journal title from NLM’s cataloging data|
|LA||Language||The language in which the article was published|
|LID||Location ID||The pii or doi that serves the role of pagination|
|LR||Last Revision Date||The date a change was made to the record|
|MH||MeSH Terms||NLM's Medical Subject Headings (MeSH) controlled vocabulary|
|MHDA||MeSH Date||The date MeSH terms were added to the citation. The MeSH date is the same as the Entrez date until MeSH are added|
|OAB||Other Abstract||Abstract supplied by an NLM collaborating organization|
|OCI||Other Copyright Information||Copyright owner|
|OID||Other ID||Identification numbers provided by organizations supplying citation data|
|ORI||Original Report In||Cites the original article associated with the patient summary|
|OT||Other Term||Non-MeSH subject terms (keywords) assigned by an organization identified by the Other Term Owner|
|OTO||Other Term Owner||Organization that provided the Other Term data|
|OWN||Owner||Organization acronym that supplied citation data|
|PG||Pagination||The full pagination of the article|
|PHST||Publication History Status Date||Publisher supplied dates regarding the article publishing process|
|PL||Place of Publication||Journal's country of publication|
|PMCR||PMC Release||Availability of PubMed Central article|
|PMID||PubMed Unique Identifier||Unique number assigned to each PubMed citation|
|PRIN||Partial Retraction In||Partial retraction of the article|
|PROF||Partial Retraction Of||Article being partially retracted|
|PS||Personal Name as Subject||Individual is the subject of the article|
|PST||Publication Status||Publication status|
|PT||Publication Type||The type of material the article represents|
|RF||Number of References||Number of bibliographic references for Review articles|
|RIN||Retraction In||Retraction of the article|
|RN||EC/RN Number||Number assigned by the Enzyme Commission to designate a particular enzyme or by the Chemical Abstracts Service for Registry Numbers|
|ROF||Retraction Of||Article being retracted|
|RPF||Republished From||Article being cited has been republished or reprinted in either full or abridged form from another source|
|RPI||Republished In||Article being cited also appears in another source in either full or abridged form|
|SB||Subset||Journal or citation subset values representing specialized topics|
|SFM||Space Flight Mission||NASA-supplied data space flight/mission name and/or number|
|SI||Secondary Source Identifier||Identifies secondary source databanks and accession numbers of molecular sequences discussed in articles|
|SO||Source||Composite field containing bibliographic information|
|SPIN||Summary For Patients In||Cites a patient summary article|
|STAT||Status Tag||Used for internal processing at NLM|
|TA||Journal Title Abbreviation||Standard journal title abbreviation|
|TI||Title||The title of the article|
|TT||Transliterated Title||Title of the article originally published in a non-English language, in that language|
|UIN||Update In||Update to the article|
|UOF||Update Of||The article being updated|
|VI||Volume||Volume number of the journal|
The data in these fields are citations to other associated journal publications, e.g., comments or errata. Often these link to the respective citation. Comments/Corrections data can be retrieved by the search term that follows each type:
Comment in: hascommentin
Comment on: hascommenton
Erratum in: haserratumin
Erratum for:: haserratumfor
Corrected and republished in: hascorrectedrepublishedin
Corrected and republished from: hascorrectedrepublishedfrom
Partial Retraction in: haspartialretractionin
Partial Retraction of: haspartialretractionof
Republished in: hasrepublishedin
Republished from: hasrepublishedfrom
Retraction in: hasretractionin
Retraction of: hasretractionof
Update in: hasupdatein
Update of: hasupdateof
Summary for patients in: hassummaryforpatientsin
Original Report in: hasoriginalreportin
Identifies the corporate or collective authorship of an article. Corporate names display exactly as they appear in the journal.
Note: Citations indexed pre-2000 and some citations indexed in 2000-2001 retain corporate authors at the end of the title field. For comprehensive searches, consider including terms and/or words searched in the title field [ti].
The date the citation record was first created.
Number assigned by the Enzyme Commission (EC) to designate a particular enzyme or by the Chemical Abstracts Service (CAS) for Registry Numbers, e.g., 1-5-20-4[rn]
Date the citation was added to the PubMed database. Exceptions: As of December 15, 2008, records that enter PubMed more than twelve months after the date of publication have the EDAT set to the date of publication. Prior to this, the Entrez Date was set to the Publication Date on citations published before September 1997.
Search results are displayed in Entrez Date order, i.e., last in, first out. The Entrez Date is not changed to reflect the date a publisher supplied record is elevated to in process or when an in process record is elevated to indexed for MEDLINE.
To enter a date range, insert a colon (:) between each date (e.g., 1996:1997 [edat] or 1998/01:1998/04 [edat]).
Note: The Entrez Date is not changed to reflect the date a publisher supplied record is elevated to in process or when an in process record is elevated to indexed for MEDLINE.
See Searching By Date for additional information.
Technical tags used by, filters include:
loall[sb] - Citations with LinkOut links in PubMed.
free full text[sb] - Citations that include a link to a free full-text article.
full text[sb] - Citations that include a link to a full-text article.
Use Preview/Index to browse the LinkOut index. Select Filter from the All Fields menu, enter 'loprov' in the search box, select Index. PubMed displays an alphabetic list of the Subject Types and Attributes. The 'loftext' entries include a link to the online full-text of a journal citation.. The 'losubj' and 'loattr' entries are links indexed by
The first personal author name in a citation.
The full author name for articles published from 2002 forward, if available. Full author searching can be entered in natural or inverted order, e.g., julia s wong or wong julia s.
The full investigator or collaborator name for articles, if available. Full investigator searching can be entered in natural or inverted order, e.g., harry janes or janes harry.
Research grant numbers, contract numbers, or both that designate financial support by any agency of the US PHS (Public Health Service), several United Kingdom granting agencies and other funding sources. The three pieces of the grant number (LM05545 - number, LM - acronym, and United States NLM - institute country and mnemonic) are each individually searchable using the [gr] tag.
Additional information about NIH grant numbers and tips for searching:
NIH grant numbers, e.g., 5R01CA101211-03, typically have three main parts:
A prefix that indicates the type of grant, e.g., 5R01
An 8-character serial number consisting of a 2-letter NIH institute/center code and a 6-digit number, e.g., CA101211
A suffix that includes additional data such as grant year
To search for an individual NIH grant number use the 8-character serial number and the [gr] tag, e.g., ca101211[gr].
Note: Grant numbers display in PubMed as they appear in the published article. If the number in the journal article is not 6 digits, e.g., CA84141, insert a leading zero, e.g., ca084141[gr], so the entire search string is a total of 8 characters long.
For a broader search, use the 2-letter grant code assigned to an agency and the [gr] tag, e.g., ca[gr]
For the broadest search, use the agency abbreviation and the [gr] tag, e.g., nci[gr]. Seefor help determining the agency abbreviation using the grant code.
Search organization names with or without the country, e.g., united states cdc[gr] or cdc[gr].
The number of the journal issue in which the article was published.
Names of principal investigator(s) or collaborators who contributed to the research. Search names following the Author field format, e.g., soller b [ir]
The journal title abbreviation, full journal title, or ISSN number (e.g., J Biol Chem, Journal of Biological Chemistry, 0021-9258).
Theis available from the PubMed homepage sidebar to look up the full name, abbreviation, and ISSN number of a journal. If a journal title contains special characters, e.g., parentheses, brackets, enter the name without these characters, e.g., enter J Hand Surg [Am] as J Hand Surg Am.
The language in which the article was published. Note that many non-English articles have English language abstracts. You can either enter the language or enter just the first three characters of most languages, e.g., chi [la] retrieves the same as chinese [la]. The most notable exception is jpn [la] for Japanese.
The last personal author name in a citation.
The doi or publisher ID that serves the role of pagination to locate an online article.
The date the citation was indexed with MeSH Terms and elevated to MEDLINE for citations with an Entrez Date after March 4, 2000. The MeSH Date is initially set to the Entrez Date when the citation is added to PubMed. If the MeSH Date and Entrez Date on a citation are the same, and the Entrez Date is after March 4, 2000, the citation has not yet been indexed.
Dates must be entered using the format YYYY/MM/DD [mhda], e.g. 2000/03/15 [mhda]. The month and day are optional (e.g., 2000 [mhda] or 2000/03 [mhda]).
To enter a date range, insert a colon (:) between each date (e.g., 1999:2000 [mhda] or 2000/03:2000/04 [mhda]).
A MeSH term that is one of the main topics discussed in the article denoted by an asterisk on the MeSH term or MeSH/Subheading combination, e.g., Cytokines/physiology* See MeSH Terms [MH] below.
MeSHare used with MeSH terms to help describe more completely a particular aspect of a subject. For example, the drug therapy of asthma is displayed as asthma/drug therapy, see MeSH/Subheading Combinations in MeSH Terms [MH] below.
The MeSH Subheading field allows users to "free float" Subheadings, e.g., hypertension [mh] AND toxicity [sh].
MeSH Subheadings automatically include theterms under the term in a search. To turn off this automatic feature, use the search syntax [sh:noexp], e.g., therapy [sh:noexp].
|Abbreviation||MeSH Subheading||Abbreviation||MeSH Subheading|
|AD||Administration and Dosage||ME||Metabolism|
|AA||Analogs and Derivatives||MO||Mortality|
|AH||Anatomy and Histology||OG||Organization and Administration|
|AI||Antagonists and Inhibitors||PS||Parasitology|
|CL||Classification||PC||Prevention and Control|
|DT||Drug Therapy||SN||Statistics and Numerical Data|
|EC||Economics||SD||Supply and Distribution|
|GD||Growth and Development||UL||Ultrastructure|
|IP||Isolation and Purification|
|LJ||Legislation and Jurisprudence|
NLM's MeSH Database.controlled vocabulary of biomedical terms that is used to describe the subject of each journal article in MEDLINE. MeSH contains more than 23,000 terms and is updated annually to reflect changes in medicine and medical terminology. MeSH terms are arranged hierarchically by subject categories with more specific terms arranged beneath broader terms. PubMed allows you to view this hierarchy and select terms for searching in the
Skilled subject analysts examine journal articles and assign to each the most specific MeSH terms applicable - typically ten to twelve. Applying the MeSH vocabulary ensures that articles are uniformly indexed by subject, whatever the author's words.
Notes on MeSH Terms and Major MeSH Topic search fields:
To search the term only as a MeSH term, it must be tagged using the search field, e.g., [mh] for MeSH Terms or [majr] for MeSH Major Topic. A tagged term is checked against the MeSH translation table. And mapped to the appropriate MeSH term. Some concepts may map to two or more MeSH terms. To turn off this mapping, enclose the MeSH term in double quotes and tag with [mh], e.g., "cold" [mh].
MeSH terms are arranged hierarchically by subject categories with more specific terms arranged beneath broader terms. MeSH terms in PubMed automatically include the more specific MeSH terms in a search. For more detailed information about MeSH vocabulary including the hierarchical structure, please see the.
MeSH/Subheading Combinations: To directly attach MeSH Subheadings, use the format MeSH Term/Subheading, e.g., neoplasms/diet therapy. You may also use the two-letter MeSH Subheading abbreviations, e.g., neoplasms/dh. The [mh] tag is not required, however [majr] may be used, e.g., plants/genetics[majr]. Only one Subheading may be directly attached to a MeSH term. For a MeSH/Subheading combination, PubMed always includes the more specific terms arranged beneath broader terms for the MeSH term and also includes the more specific terms arranged beneath broader . The broader Subheading, or one of its indentions’, will be directly attached to the MeSH term or one of its indentions’. For example, hypertension/therapy also retrieves hypertension/diet therapy; hypertension/drug therapy; hypertension, malignant/therapy; hypertension, malignant/drug therapy, and so on, as well as hypertension/therapy.
To turn off the automatic inclusion of the more specific terms, use the syntax [field:noexp], e.g., hypertension [mh:noexp], or hypertension [majr:noexp], or hypertension/therapy [mh:noexp]. The latter example turns off the more specific terms in both parts, searching for only the one Subheading therapy attached directly to only the one MeSH term hypertension.
If parentheses are embedded in a MeSH term, replace the parentheses with a space and tag with [mh] e.g., enter the MeSH term Benzo(a)pyrene as benzo a pyrene [mh].
MeSH terms can be selected for searching in the Preview/Index.and from
The alpha-numeric identifier for the cited journal that was assigned by NLM's Integrated Library System, e.g., 0375267 [jid].
Mostly non-MeSH subject terms (keywords), including NASA Space Flight Mission, assigned by an organization other than NLM. The Other Term data may be marked with an asterisk to indicate a major concept, however asterisks are for display only. You cannot search Other Terms with a major concept tag. The OT field is searchable with the Text Word [tw] and Other Term [ot] search tags.
Acronym that identifies the organization that supplied the citation data. Search using owner + the owner acronym, e.g. ownernasa.
Enter only the first page number that the article appears on. The citation will display the full pagination of the article but this field is searchable using only the first page number.
Use this search field tag to limit retrieval to where the name is the subject of the article, e.g., varmus h[ps]. Search names following the Author field format, e.g., varmus h[ps].
Substances known to have a particular pharmacologic action. Each pharmacologic action term index is created with the drug/substance terms known to have that effect. This includes both MeSH terms and terms for Supplementary Concept Records.
Indicates the cited journal's country of publication. Geographic Place of Publication regions are not searchable. In order to retrieve records for all countries in a region (e.g., North America) it is necessary to OR together the countries of interest. Note: This field is not included in All Fields or Text Word retrieval.
Search for PubMed Central or Manuscript Identifiers using the appropriate prefix followed by the ID number, e.g., PMC2600426.
The date that the article was published.
Dates or date ranges must be searched using the format YYYY/MM/DD [dp], e.g. 1998/03/06 [dp]. The month and day are optional (e.g., 1998 [dp] or 1998/03 [dp]).
To enter a date range, insert a colon (:) between each date (e.g., 1996:1998 [dp] or 1998/01:1998/04 [dp]).
Use the following format to search X days, months or years immediately preceding today’s date where X = numeric value:
“last X days”[dp]
“last X months”[dp]
“last X year”[dp]
Journals vary in the way the publication date appears on an issue. Some journals include just the year, whereas others include the year plus month or year plus month plus day. And, some journals use the year and season (e.g., Winter 1997). The publication date in the citation is recorded as it appears in the journal.
If an article is published electronically and in print on different dates both dates are searchable and may be included on the citation prefaced with an Epub or Print label. The electronic date will not be searchable if it is later than the print date, except when range searching.
To search for electronic dates only use the search tag [EPDAT], for print dates only tag with [PPDAT].
|See complete list of. Publication types found in PubMed are listed below.|
|Clinical Trial [includes all types and phases of clinical trials]
|Corrected and Republished Article|
|Consensus Development Conference|
|Consensus Development Conference, NIH|
Introductory Journal Article
|Patient Education Handout|
|Retraction of Publication|
|Randomized Controlled Trial|
|Scientific Integrity Review|
The SI field identifies secondary source databanks and accession numbers, e.g., GenBank, GEO, PubChem, ClinicalTrials.gov, ISRCTN. The field is composed of the source followed by a slash followed by an accession number and can be searched with one or both components, e.g., genbank [si], AF001892 [si], genbank/AF001892 [si].
The SI field and the NCBI sequence database links are not linked. The PubMed links to these databases are created from the reference field of the GenBank or GenPept flat file. These references include citations that discuss the specific sequence presented in these flat files.
Method of restricting retrieval by topic, citation status and journal/citation subsets. Searchable with [SB]. See also Limits and Finding Related Links for a Citation Using LinkOut).
The name of a chemical discussed in the article. Synonyms to the Supplementary Concept Substance Name will automatically map when tagged with [nm]. This field was implemented in mid-1980. Many chemical names are searchable as MeSH terms before that date.
Includes all words and numbers in the title, abstract, other abstract, MeSH terms, MeSH Subheadings, Publication Types, Substance Names, Personal Name as Subject, Corporate Author, Secondary Source, and Other Terms (see Other Term [OT] above) typically non-MeSH subject terms (keywords), including NASA Space Flight Mission, assigned by an organization other than NLM.
Words and numbers included in the title of a citation.
Words and numbers included in the title, abstract, and other abstract of a citation. English language abstracts are taken directly from the published article. If an article does not have a published abstract, NLM does not create one.
Words and numbers in title originally published in a non-English language, in that language. Non-Roman alphabet language title are transliterated. Transliterated title is not included in All Fields or Text Word retrieval so you must search terms using the [tt] search tag.
PubMed Unique Identifier PMID.
To search for a PMID enter the number with or without the search field tag [pmid]. You can search for several PMIDs by entering each number in the search box separated by a space (e.g., 17170002 16381840); PubMed will OR the PMIDs together.
To search in combination with other terms, you must enter the search field tag, e.g., smith [au] AND (pubmed AND 16381840[pmid]).
The number of the journal volume in which an article is published.
Searching by author
Searching by journal title
Searching by date
Limit your searches (Limits)
Searching for a phrase
Truncating search terms
Combining searches (History)
Finding a citation using the Single Citation Matcher
Browsing PubMed's index of terms (Preview/Index)
Combining search terms with Boolean operators (AND, OR, NOT)
Searching in a specific field or index
Previewing the number of search results (Preview/Index)
Finding articles related to a citation
Using Clinical Queries
Finding systematic reviews
Identify the key concepts in your research question.
|Find citations about bronchodilators for treating asthma in children.|
|The key concepts are|
Enter the significant terms into the search box.
Press the Enter key or click Go.
Achecking feature suggests alternative spellings for PubMed search terms that may include misspellings.
A Citation Sensor displays results for searches that include terms characteristic of citation searching, e.g., author names, journal titles, publication dates, and article titles.
A Gene Sensor checks queries, and if it detects the symbol for a gene, links to the.
A Drug Sensor identifies drug names in queries and then links to the Bookshelf:.
Recent Activity displays your recent database searches and document views.
Additional discovery ads may display alongside your results.
To modify your current search, change your search terms in the search box.
Enter in the search box one of the following:
full journal title (e.g., molecular biology of the cell)
title abbreviation (e.g., mol biol cell)
ISSN number, a standardized international code (e.g., 1059-1524)
To find full journal names, use the.
Click Journals Database on the PubMed sidebar.
Enter the journal name and click Go.
Check the Suggestions if the journal name does not display in the results.
Choose PubMed under the Links menu to search for the journal.
More information about journal searching:
Use the Single Citation Matcher that includes a journal autocomplete feature.
Click the Limits tab to use the journal search builder that also includes an autocomplete feature.
If a journal title is also a MeSH term (e.g., Gene Therapy, Science, or Cell), PubMed will search the untagged term as MeSH. Tag the journal title by using the Journal Title search field [ta] to search for the journal (e.g., gene therapy[ta]).
If a journal title is a single word, tag the title using the Journal Title search field (e.g., scanning [ta]). Otherwise, PubMed will search the untagged single word journal title as a MeSH term (if applicable) or as All Fields.
Searching with the full journal title or title abbreviation is recommended for complete retrieval of indexed items; older citations may not have an ISSN.
If a journal title or title abbreviation includes a special character (e.g., parentheses, brackets, &), enter the title or abbreviation without the special characters. For example, to search j hand surg [am], enter j hand surg am.
Searching for a journal will automatically map to the official journal title and the title associated with an alternative title, if one exists. To turn off this automatic mapping enclose the journal in double quotes and tag with [ta].
Athat are included in the PubMed database is available by FTP in the Uncompressed, GNU Zip, UNIX Compress, or PKZIP format.
Click the Limits tab.
You may limit your search to articles published or added to PubMed by a pre-set date range by choosing the date range from the Dates menus.
You may also enter any desired date range by selecting Specify date range (YYYY/MM/DD) under the menus. Enter a single date or a date range in the fill-in-the-blank boxes. Month and day are optional. If you want to search for a date range up to the current date, leave the To date boxes blank.
Select additional search limits or add search terms to the search box, if desired. Click Go.
When you start a new search, turn off the Date limit by clicking the Limits tab check box.
More information about date searching:
Enter dates using the format YYYY/MM/DD [date field]. There is a selection of date fields to use:
Date of Publication [dp] - Date searching includes both print and electronic dates of publication. Searching for a single date does not include items when the electronic date of publication is after the print date.
Electronic Date of Publication (if applicable) [epdat]
Print Date of Publication (if applicable) [ppdat]
Entrez Date [edat] - The date the citation first entered PubMed.
MeSH Date [mhda] - The date the citation was indexed with MeSH terms.
Create Date [crdt] – The date the citation record was first created.
The month and day are optional.
Enter date ranges using a colon (:) between each date followed by a [date field].
Comprehensive searches for a full year should be entered as 2000:2000[dp] rather than 2000[dp] to retrieve citations with a different print and electronic year of publication.
Date range searching includes both print and electronic dates of publication.
Use the following format to search for a relative date range:
term="last X days"[Search Tag]
term="last X months"[Search Tag]
term="last X years"[Search Tag]
where X is the number of days, months or years immediately preceding today’s date and [Search Tag] is the date search tag: [dp], [edat] or [crdt].
Limits also includes a search builder for authors and journals.
Click the Limits tab.
You may enter an author or journal.
Choose any limit selections from the options available on the page.
If necessary, make changes to the search terms in the search box or enter a new search.
The "in process" and "supplied by publisher" citations may be excluded for some limit selections because they have not yet completed the MEDLINE indexing process and may not include these data.
When Limits are “in effect” a check will appear in the Limits tab and your selected limits will display in a yellow bar. To turn off limits click off the Limits tab check box and run a new search.
Go and Clear All Limits buttons are available at the bottom of the Limits page. The Go button function at the top and bottom of the page is equivalent.
To search by author, click Add Author.
An author search box will display. The author search box includes an autocomplete feature; enter a name in the Author name box and you will see a list of suggested names that gets shorter as you type more letters. As soon as you see the author name you are looking for, you may select that name.
To add additional authors, click the Add Another Author link to open another author search box. The default author search is to include all author names in your search. To change this to search for any authors you selected click the radio button from All these authors to Any of these. Click the remove link to delete an author search box.
Author names will automatically move to the PubMed search box when you click Go.
Selected limits will be activated for any subsequent searches except for authors and journals. Author and journal selections will only be included in subsequent searches if they are not cleared from the PubMed search box.
To search by journal, click Add Journal.
The journal search box also includes an autocomplete feature; enter a name in the journal name box and you will see a list of suggested names that gets shorter as you type more letters. As soon as you see the journal title you are looking for, you may select it.
To add additional journals, click the Add Another Journal link to open another journal search box.
Search results will include any of the selected journals.
Journals will automatically move to the PubMed search box when you click Go. Author and journal selections will only be included in subsequent searches if they are not cleared from the PubMed search box.
To limit your search results to only citations that include a link to full text, a link to free full text, or an abstract, click the appropriate check boxes.
Alternatively, you may search for citations with links to full text, free full text or include an abstract using the values: full text[sb], free full text[sb], or 'hasabstract'. No search field tag is required for hasabstract.
Note: Most citations in PubMed to articles published before 1975 do not include abstracts.
You may limit your search to articles published or added to PubMed by a pre-set date range, e.g., in the last 60 days; or you may enter any desired date range by selecting Specify date range (YYYY/MM/DD) from the Dates menus.
If you select Specify date range from a date Dates menu, enter a single date or a date range in the fill-in-the-blank boxes. Month and day are optional. If you want to search for a date range up to the current date, leave the To date boxes blank.
PubMed displays search results when the citation was added in descending order, i.e., last in, first out.
The Humans or Animals limit restricts your search to a human or animal study.
With this limit, PubMed retrieval will be limited to MEDLINE citations. The "in process" and "supplied by publisher" citations will be excluded because they have not yet completed the indexing process and do not carry these data.
The gender limit restricts your search to a specific gender for a human study.
With this limit, PubMed retrieval will be limited to MEDLINE citations. The "in process" and "supplied by publisher" citations will be excluded because they have not yet completed the indexing process and do not carry these data.
The languages limit restricts your search to articles written in a particular language.
Languages initially displays a list of the most frequently used languages:
The complete list of languages is available under the More Languages label.
|Subset Code||Journal/Citation Subset|
|AIM||is a list created in 1970 of approximately 120 core clinical English language journals that corresponds to "Core clinical journals" subset in Limits.|
|E||Citations from bioethics journals or selected bioethics citations from other journals|
|H||Health administration journals, non-Index Medicus|
|IM||Index Medicus journals|
|K||Consumer health journals|
|Q||History of medicine journals and selected citations from other journals|
|QIS||Citations from non-Index Medicus journals in the field of history of medicine|
|S||Citations from space life sciences journals and selected space life sciences citations from other journals|
|T||Health technology assessment journals, non-Index Medicus|
|X||AIDS/HIV journals (selected citations from other journals 1980-2000)|
To search for a Journal/Citation subset, enter in the search box: jsubset?, where ? represents the subset value.
|This search will limit retrieval to citations from bioethics journals or selected bioethics citations from other journals.|
The Journal/Citation subset does not require a search tag.
The topics subsets restrict retrieval to specific subjects including:
History of Medicine
Space Life Sciences
Each topic subset limit uses its own specialized.
Alternatively, each topic subset can be searched using the respective search value of aids, bioethics, cancer, cam, history, space, systematic or tox followed by the [sb] search tag.
Do not confuse the topic subsets for AIDS, Bioethics, Cancer, History of Medicine, and Space Life Sciences with the journal or other subsets (see below) for the same topics, i.e., jsubsetx, jsubsete, jsubsetq, and jsubsets.
This subset restricts retrieval to citations that have a full-text article available for free in(PMC).
To search for PubMed Central citations use Limits Subsets, or simply enter pubmed pmc local[sb] into the search box.
To search for all citations that have free full-text articles available (both PMC citations and citations where the free full-text article is provided directly from the journal’s Web site in PMC), enter pubmed pmc[sb] in the search box.
Use theto translate one type of ID to the other.
|Status Tag||How to Search||Citation Status|
|PubMed - as supplied by publisher||publisher[sb] NOT pubstatusnihms NOT pubstatuspmcsd||Citations recently added to PubMed via electronic submission from a publisher, and are soon to proceed to the next stage, PubMed - in process (see below). This tag is also on citations received before late 2003 if they are from journals not indexed for MEDLINE, or from a journal that was accepted for MEDLINE after the citations' publication date. These citations have not been reviewed for accurate bibliographic data.|
|PubMed - in process||in process[sb]||Citations will be reviewed for accurate bibliographic data and indexed, i.e., the articles will be reviewed and MeSH vocabulary will be assigned (if the subject of the article is within the scope of MEDLINE).|
|PubMed - indexed for MEDLINE||medline[sb]||Citations that have been indexed with MeSH Terms, Publication Types, Substance Names, etc., and have been reviewed for accurate bibliographic data.|
|PubMed||pubstatusnihms AND publisher[sb]||Author manuscripts for articles in PubMed Central that would not normally be included in PubMed because they are from journals that are either not currently indexed or are selectively indexed in MEDLINE or do not participate in PMC.|
|PubMed||pubstatuspmcsd AND publisher[sb]||Records for selective deposit articles in PMC. These are articles published in non-MEDLINE journals and the publisher has chosen to deposit in PMC only those articles that fall under an open access or a similar program covering selected articles from a range of journals.|
|PubMed||pubmednotmedline[sb]||Citations that have been reviewed for accurate bibliographic data but will not receive MEDLINE indexing, because they are for articles in non-MEDLINE journals, or they are for articles in MEDLINE journals but the articles are out of scope or they are from issues published prior to the date the journal was selected for indexing, or citations to articles from journals that deposit their full text articles in PubMed Central but have not yet been recommended for indexing in MEDLINE.|
|PubMed - OLDMEDLINE||oldmedline[sb]||This tag identifies citations in thesubset.|
The status tags are displayed with each citation in the search results. To search for a particular citation status, enter one of the search terms below followed by the [sb] search tag
To search for the total number of PubMed citations, enter all [sb] in the search box.
Note: The MEDLINE subset can be selected from More Subsets in Limits.
Publishers may submit citations for articles that appear on the Web in advance of the journal issue's release. These are ahead-of-print citations.
To search for ahead of print citations, enter pubstatusaheadofprint into the search box
Following publication of the completed issue, the date an article was published electronically is retained on these citations, e.g. Proc Natl Acad Sci U S A. 2003 Apr 1;100(7):3925-9. Epub 2003 Mar 24.
The publication type limit will restrict your search based on the type of material the article represents, such as:
Randomized Controlled Trial
The complete list of publication types is available under the Limits Type of Article More Publication Types.
With this limit, PubMed retrieval will be limited to MEDLINE citations. The "in process" and "supplied by publisher" citations will be excluded because they have not yet completed the indexing process and will not include a Publication Type.
The Limits age groups restrict your search to a specific age group for a human study, and include:
All Infant: birth-23 months
All Child: 0-18 years
All Adult:19+ years
Newborn: birth-1 month
Infant: 1-23 months
Preschool Child: 2-5 years
Child: 6-12 years
Adolescent: 13-18 years
Adult: 19-44 years
Middle Aged: 45-64 years
Middle Aged + Aged: 45+ years
Aged: 65+ years
80 and over: 80+ years
With this limit, PubMed retrieval will be limited to MEDLINE citations. The "in process" and "supplied by publisher" citations will be excluded because they have not yet completed the indexing process and do not carry these data.
To limit untagged search terms to a specific citation field choose a field from the Tag Terms All Fields menu located at the bottom of the Limits page.
See Also: Searching in a specific field of index
PubMed does not perform adjacency searching. However, many phrases are recognized by the MeSH Translation Table used in PubMed's Automatic Term Mapping (ATM) feature. For example, if you enter fever of unknown origin, PubMed recognizes this phrase as a MeSH concept. If a phrase is not recognized you can instruct PubMed to bypass ATM and search for a phrase using the formats outlined below.
More information for phrase searching:
If you use a hyphen or quotes and the phrase is not found, the hyphen or quotes are ignored and the phrase is processed using automatic term mapping. Phrases may appear in a PubMed record but not be in the phrases index.
When you enter your search terms as a phrase PubMed will not perform automatic term mapping that includes explosion of MeSH terms. For example, "health planning" will include citations that are indexed to the MeSH term, Health Planning, but will not include the more specific terms, e.g., Health Care Rationing, Health Care Reform, Health Plan Implementation, etc., that are included with the automatic MeSH mapping.
Truncating a word in a multi-word search may result in an unexpected phrase search. For example the search, fetus infection* maternal will treat fetus infection* as a phrase. Check Details to see the search translation.
To search for all terms that begin with a word, enter the word followed by an asterisk (*).
|Finds terms that begin with the root term flavor, such as flavored, flavorful, flavoring, etc.|
More information about truncation:
PubMed searches for the first 600 variations of a truncated term. If a truncated term (e.g., tox*) produces more than 600 variations, PubMed displays a warning message to lengthen the root word to search for all endings.
Truncation turns off automatic term mapping and the automatic explosion of a MeSH term. For example, heart attack* will not map to the MeSH term Myocardial Infarction or include any of the more specific terms, e.g., Myocardial Stunning; Shock, Cardiogenic.
Truncating a word in a multi-word search may result in an unexpected phrase search. For example the search, fetus infection* maternal will treat fetus infection* as a phrase.
Previous searches can be combined or used in subsequent searches using the search statement number from History.
Click the History tab.
Click on the linked search statement number to display the options menu that includes Boolean operators to AND, OR or NOT your search to the search box. Alternatively you can enter a number sign followed by the search number, e.g., #1, in the search box.
Add additional search terms into the search box or combine with other searches.
|#2 AND #6|
|#3 AND (drug therapy OR diet therapy)|
|#5 gene therapy|
For additional information, see Viewing your search history.
The Single Citation Matcher has a fill-in-the-blank form for searching for a citation when you have some bibliographic information, e.g., journal name, volume, page number.
Clickon the PubMed sidebar.
Enter the bibliographic information you have.
More information about using the Single Citation Matcher:
The journal box includes an autocomplete feature that suggests titles as you enter a title abbreviation or full title. Titles displayed by the autocomplete menu are in ranked order based on the number of citations in PubMed.
After selecting a journal with special characters (e.g., ampersand, colon) when using the Back button to return to the Single Citation Matcher you must clear and reenter the title.
The author box also includes an autocomplete feature that suggests author names in ranked order based on the number of citations. Full author names may be searched for citations published from 2002 forward if the full author name is available in the article.
Click either the 'Only as first author' or ‘Only as last author’ check box to limit an author name to the first or last author.
Preview/Index provides an alphabetical display of all search terms in each PubMed search field. You can browse by all fields or within a specific field such as MeSH Terms.
Click the Preview/Index tab.
Select a search field from the All Fields menu at the bottom of the page.
Enter a search term in the search box. If you want to see a list of all terms, leave the search box empty.
PubMed displays an alphabetic list of search terms. The number of citations for that term appears in parentheses to the right of the term. Click Up or Down to move within the Index.
Select a term. To select multiple terms (and OR them together), select on each term while holding down the Ctrl key (PC) or the Command key (Mac).
Click the appropriate Boolean operator to add the search term to the search box. Be sure to clear the search box before beginning a new search.
Continue adding terms (repeating steps 2 to 7), if desired.
Click Go. If you only want to preview the number of results, click Preview.
More information about using the index:
Preview/Index displays the last three searches from History. History retains the last 100 searches.
PubMed processes all Boolean operators left to right. To change this order, enclose search terms to be processed first in parentheses, e.g., common cold AND (vitamin c OR zinc). PubMed will automatically OR (and add parentheses) for multiple terms selected from the Index.
PubMed assumes the AND operator between concepts, e.g., “vitamin c common cold” is translated as vitamin c AND common cold. Enter Boolean operators in uppercase characters to combine or exclude search terms:
AND retrieves results that include all the search terms.
OR retrieves results that include at least one of the search terms.
NOT excludes the retrieval of terms from your search.
|Find citations on DNA that were authored by Dr. Crick in 1993:|
|Find articles on the effects of heat or humidity on multiple sclerosis:|
|Find citations about arthritis excluding the Publication Type Letter:|
PubMed processes searches in a left-to-right sequence. Use parentheses to “nest” concepts that should be processed as a unit and then incorporated into the overall search.
More information about using Boolean operators:
Boolean operators must be used when combining tagged search terms as follows: search term [tag] BOOLEAN OPERATOR search term [tag]. (See Search Field Descriptions and Tags)
In a multi-word search PubMed will use Automatic Term Mapping to identify concepts. For example, for the search air bladder fistula, PubMed will search "air bladder" as a phrase. If you do not want this automatic phrase parsing, enter each term separated by the Boolean operator AND, e.g., air AND bladder AND fistula.
Click Details to see how PubMed translated your search strategy.
To search a specific field in a citation (e.g., author, title, journal, etc.) and bypass the automatic term mapping, tag the search term by adding the appropriate search tag (Search Field Descriptions and Tags).
The search tag must be enclosed in square brackets.
Case and spacing do not matter (e.g., crabs [mh] = Crabs[mh])
To preview the number of citations before displaying the search results:
Click the Preview/Index tab.
Enter your search term(s) in the search box.
Click Preview. The number of results is displayed.
To display the citations, click the result link.
Use Preview to add search terms incrementally to refine your search before retrieving the citations.
Enter a search term in the search box.
Click Preview. The number of results is displayed.
Continue adding terms and selecting Preview until your search is complete.
Note: Preview displays the last three searches from History. History retains the last 100 searches.
Click the Related Articles link on the right side of a citation.
The Related Articles link will retrieve a pre-calculated set of PubMed citations that are closely related to the selected article. The related articles will be displayed in ranked order from most to least relevant, with the “linked from” citation displayed first.
More information about Related Articles:
The AbstractPlus display automatically includes the first 5 Related Article citations.
Each citation in PubMed includes a link that retrieves a pre-calculated set of citations that are closely related to the selected article. PubMed creates this set by comparing words from the title, abstract, and MeSH terms using a word-weighted algorithm.
If you select Related Articles from the Display menu without selecting specific citations, PubMed will retrieve the related articles for the citations displayed on the page.
Limits are NOT in effect when you use a Related Articles link. After linking on Related Articles, although the box next to Limits may be checked, there is no yellow bar displaying the Limits in effect.
You can, however, refine the list of Related Articles using PubMed’s History feature. In History, you will see that the Related Articles retrieval is represented as "Link to PubMed from (PMID of document)." Use this Search number in a search. (Keep in mind that the list you get with a Related Articles link is displayed in ranked order from most to least relevant. Refining the list removes the ranked order and may remove citations that are most relevant.)
Use theutility to retrieve related articles for large sets of citations.
The PubMed Clinical Queries page provides specialized PubMed searches for clinicians:
Search by Clinical Study Category
Finding Systematic Reviews
Medical Genetics Searches
The Clinical Study Category is a specialized search method with built-inthat limit retrieval to citations to articles reporting research conducted with specific methodologies, including those that report applied clinical research.
To find citations using the Clinical Study Category:
Click Clinical Queries from the PubMed sidebar
Click Search by Clinical Study Category
Enter your search term in the search box
Select a Category: therapy, diagnosis, etiology, or prognosis
Select a Scope: “narrow, specific search or broad, sensitive search
|Find research on diagnosing cystic fibrosis.|
|On the Clinical Queries page click Search by Clinical Study Category.|
|Enter cystic fibrosis in the search box.|
|Click “diagnosis” under Category and “narrow, specific search” under Scope, click.|
In PubMed, Systematic Reviews cover athat build consensus on biomedical topics. This feature is provided to help clinicians locate systematic reviews and similar articles.
To find Systematic Reviews:
Click Clinical Queries from the PubMed sidebar
Click Find Systematic Review
Enter your search terms in the search box
|Find Systematic Reviews on inhalation therapy for pneumonia.|
|On the Clinical Queries page click Find Systematic Reviews.|
|Enter the search terms inhalation therapy pneumonia into the search box, click.|
Alternatively, enter search terms followed by AND systematic[sb] into the search box. For example, lyme disease AND systematic[sb].
In PubMed, Medical Genetics Searches finds citations related to various topics in medical genetics.
Click Clinical Queries from the PubMed Sidebar
Select Medical Genetics Searches
Enter search terms in the search box
Change the search categories, if applicable
|Find information on genetic counseling for sickle cell anemia.|
|On the Clinical Queries page, click Medical Genetic Searches.|
|Enter the search terms sickle cell anemia into the search box.|
|Under Category, click on All to deselect all the categories, click Genetic Counseling, click.|
More information about Clinical Queries:
The Clinical Study Category search filters are based on the work of. See the for details.
Systematic Reviews uses a customized. A list of on this topic is provided.
In PubMed, systematic reviews cover a broad set of articles that build consensus on biomedical topics and include:
reviews of clinical trials
consensus development conferences
citations from journals specializing in clinical review studies
The Medical Genetics Searches were developed in conjunction with the staff of GeneReviews: Genetic Disease Online Reviews at GeneTests, University of Washington, Seattle. The Medical Genetic Searches use built-in search.
The results of these searches can be refined using PubMed’s Limits (e.g., English language).
Search results initially display in a summary format in the order they were entered in PubMed as last in, first out. You can change the display format.
A default of 20 citations is displayed per page. If there are more than 20 citations, they will be displayed on subsequent pages.
To display the abstract for a journal article, click the title link for each citation. Some citations do not have abstracts and will include the note “No abstract available.”
For additional information see: Displaying and Sorting Your Search Results
Use the Action Bar, located at the top and bottom of the search results, for:
Changing the citation display format
Changing the number of citations shown per page
Sorting your search results
Using "Send to" for:
Search results also provide a way to:
From the Sort menu, select a sort field: publication date, first author, last author, journal, title.
More information about sorting:
Citations in PubMed are displayed in reverse date added order: last in, first out. The added date is the date that a record was initially added to PubMed and should not be confused with the publication date, which is the date an article was published.
Publication Date sorts the most recent citations first, the secondary sort is journal.
Publication dates without a month are set to January, multiple months (e.g., Oct-Dec) are set to the first month, and dates without a day are set to the first day of the month. Dates that include a season are set as: winter = January, spring = April, summer = July and fall = October.
First author, last author and journal sort A to Z; the secondary sort is publication date.
The Action Bar displays the number of citations retrieved and the number of pages of to display all the citations for your search. You may change the number of citations shown per page using the Show menu. This is especially helpful when printing your results.
To move to a specific result page enter the page number in the Page box and click the Page button, or click the Previous or Next links to move back or forward to adjacent pages. For you to use this feature your Web browser must be set to accept cookies.
Results are initially displayed in the Summary format except results that retrieve a single citation which will display the AbstractPlus view. You can change the display for all or selected citations by selecting a new display format from the Display menu.
Note: Use My NCBI to change the display for a single citation.
To change the display format only for selected citations, click the check box to the left of each citation before selecting a display format.
|Display Format||Format Description|
|This format may include: Authors, Corporate Authors, Title (Titles originally published in a language other than English are translated and displayed in brackets), Journal source, Review Publication Type, language if the article is not in English, "No abstract available" notation, PMID, Comment/Correction links, and citation status. Summary also displays when the full article is available free in.|
|Authors, first 30 characters of the Title, and PMID.|
|This format may include: Journal source, Comment/Correction links, Title, language if article is not in English, Authors, Collaborators, Corporate Author, Author Affiliation, Abstract (if present), Personal Name as Subject, PMID, citation status and the first 5 Related Articles. Search links are available for Journal Title Abbreviations, Authors and Personal Name as Subject. Click a field search link to display a menu with NCBI database search options. Click an author name to search for that author in PubMed.|
|This format may include: Journal source, Comment/Correction links, Title, language if article is not in English, Authors, Collaborators, Corporate Author, Author Affiliation, Abstract (if present), Publication Types (except for the Journal Article publication type), Personal Name as Subject, PMID, and citation status. Search links are available for Journal Title Abbreviations, Authors, Publication Types and Personal Name as Subject. Click a field search link to display a menu with NCBI database search options. Click an author name to search for that author in PubMed.|
|This format may include: Journal Source, Comment/Correction links, Title, language if article is not in English, Authors, Collaborators, Corporate Author, Author Affiliation, Abstract (if present), Publication Types (except for the Journal Article publication type), MeSH Terms, Personal Name as Subject, Chemical Substances, Secondary Source databank accession numbers, Grant numbers, PMID, and citation status. Search links are available from Journal Title Abbreviations, Authors, MeSH Terms, Publication Types, Substances, Grant Support, Secondary Source ID, and Personal Name as Subject. Click a field search link to display a menu with NCBI database search options. Identifiers may also link to other databases such as ClinicalTrials.gov and ISRCTN.|
|Two-character tagged field format (Table 8) for the complete record. Use this format to export citations into reference management programs.|
|ASN.1 (Abstract Syntax Notation One) is an international standard used to achieve inter-operability between platforms, including computer-to-computer, pager-to-computer, and many other possible combinations.|
|EXtensible Markup Language tagged format is a standard maintained by the World Wide Web Consortium (W3C). PubMed XML output conforms to several. Users running scripts to downloading data in XML should use the rather than the Web version of PubMed. A document describing the data element descriptions is available.|
|Use this format with Send to File or Text to list only PMIDs.|
You can also display links from PubMed citations to other databases (e.g., Nucleotide Links) from the Display menu.
From the Show menu, select the number of citations you want displayed per page.
More information for changing number if citations shown per page:
PubMed displays your search results in the default 20 citations per page. You can change the number of citations displayed on a single page from 5 to 500 items.
To display all citations on a single page, select a number higher than the total number of your search results.
Linking to other NCBI databases
Finding related links for a citation using LinkOut
Finding References for a PubMed Central article
Finding PubMed Central articles that have cited an article
Finding Bookshelf books that have cited an article
Reporting broken or problem links
Links to other resources or NCBI databases are available from the Links menu to the right of each citation and from the Display menu. PubMed typically only processes the first 5,000 items with links when using the Display menu. The complete list ofand the maximum items processed is available.
The Abstract, AbstractPlus and Citation displays also include search links to PubMed, MeSH and other NCBI databases. Search links are for the exact term displayed; variant forms of a term are not searched.
Note: To simultaneously search all NCBI databases use the.
The References for this PMC Article link is available when there is a full text article in PMC for a PubMed citation. The link displays the PubMed references for the PMC article.
The Cited in PMC link is available for PubMed citations cited byarticles. The Cited in PMC link lists the articles in PMC for the cited PubMed citation.
In your search results, click the citation check boxes. If you do not make any selections, PubMed will select all citations on the page.
From the Display menu, select “Cited in PMC.”
The Cited in Books link is available for PubMed citations cited in the bibliography of a Book in the.
In your search results, click the citation check boxes. If you do not make any selections, PubMed will select all citations on the page.
From the Display menu, select “Cited in Books.”
Links are supplied by the LinkOut providers. Publishers who electronically supply their data to PubMed may include an icon link to a site providing the full-text. Corrections and changes to links are made by the providers and are their responsibility.
To report problem links or inquire about electronic journal subscriptions, contact the provider directly. You can usually find a contact link at the provider's Web site.
Click the History tab, after you run your first search, to display your searches in the order they were run. To view the results for a search, click on the number of results.
PubMed may modify or add additional search terms to your search to optimize retrieval.
More information about Details:
The Query Translation box shows the search strategy used to run the search.
To edit the search in the Query Translation box, add or delete terms and then click Search.
Click URL to display the current search as a URL to bookmark for future use. Searches created using History numbers can not be saved using the URL feature.
You may also save your search using My NCBI.
The Result number link displays the total number of citations for the search.
Translations details how each term was translated using PubMed's search rules and syntax.
User Query shows the search terms as you entered them in the search box and any syntax errors with the query.
If your last action was displaying related article citations or selected items in another format, Details will indicate this rather than the last query.
Use the Printer selection under the Sent to menu on your search results or the print function of your Web browser.
To display a printer-friendly version:
In your search results, click the citation check boxes. If you do not make any selections, PubMed will select all citations on the current page.
From the Send to menu, select Printer.
Click Print this page and use the Print Dialog box to choose your printer and print.
Click Close this window to return to your search results after printing.
More information about printing:
If your Web browser is set to block pop-ups, you may need to allow pop-ups from NCBI or other NLM Web pages to display the PubMed printer page.
If you use the print function of your Web browser consider displaying citations as plain text by selecting Text from the Send to menu before printing.
To print citations from different searches, save the citations in PubMed’s Clipboard, then print or use Send to Printer from the Clipboard.
Saving citations as a text file
Exporting citations into a reference management program
Saving searches with My NCBI
Saving searches as RSS (Really Simple Syndication) feeds
Creating a URL to bookmark your search
The Clipboard gives you a place to collect selected citations from one or several searches. The Clipboard will be lost after 8 hours of inactivity on PubMed or on any of the other databases.
You may also save your search results indefinitely using My NCBI Collections.
To add citations to the Clipboard:
In your search results, use the citation check boxes to select citations. To save all your citations do not click any check boxes.
From the Send to menu, select Clipboard.
To view your selections, click the Clipboard tab.
To delete citations from the Clipboard:
Use the check boxes to select citations. To delete all citations, do not click any check boxes.
From the Send to menu, select Clip Remove.
More information about the Clipboard:
The Clipboard displays an asterisk if items have been added and a mouseover of the Clipboard tab displays the number of items.
The maximum number of items that can be sent to the Clipboard is 500. If you select Clipboard from the Send to menu without selecting citations using the check box, PubMed will add all (up to 500 citations) of your search results to the Clipboard.
The Clipboard will not add a citation that is currently in the Clipboard; it will not create duplicate entries.
Citations in the Clipboard are represented by the search number #0, which may be used in Boolean search statements. For example, to limit the citations you have collected in the Clipboard to English language articles, use the following search: #0 AND english [la]. This does not affect or replace the Clipboard contents.
In your search results, use the citation check boxes to select citations. You may move to other pages to continue your selections. If you do not make any selections, PubMed will save the entire retrieval.
From the Display menu, select a display format.
From the Send to menu, select File.
Your Web browser will prompt you to save the PubMed search results in a file on your computer.
More information about saving citations to a file:
Saving a large retrieval may take several minutes.
The default for the Send to File feature is to save the entire retrieval unless you select specific citations. For example, if you use the Send to File feature on a screen displaying 1-20 items of 2,356, your saved file will contain all 2,356 citation.
To save citations in HTML format, use the Save as... function of your browser. Change the file extension to html. When saving as HTML, only those citations displayed on the page will be saved so you may want to consider changing the number of citations shown per page.
Reference management software includes programs such as EndNote, Reference Manager, and ProCite. Questions regarding these commercial software packages should be directed to the respective companies.
In your search results, use the citation check boxes to select citations. To export all the citations do not select any citations.
From the Display menu, select MEDLINE.
From the Send to menu, select File.
Import this file to your reference management program.
In your search results, use the check boxes to select citations. To e-mail all citations displayed on the page, do not make any selections.
From the Send to menu, select E-mail.
Choose selections for Format, Sort, HTML or Text.
Enter an e-mail address. You may also enter a message that will be included with the search results e-mail.
Click Mail. The system returns you to your results page and displays a message confirming that the e-mail message was sent.
Note: Use My NCBI to setup an automatic e-mailing of search updates.
Your PubMed results will be sent from the NCBI automatic mail server, Sent by Entrez [email@example.com], with a "Subject" of PubMed Search Results. Do not reply to this message. This is not a functioning customer service e-mail address.
More information about e-mailing citations:
You may e-mail up to 500 items at a time to a single e-mail address.
The search will be included in your results email, or a notation indicating the selected items count.
If you choose HTML, your PubMed e-mail message displays as a PubMed results page and includes links to Related Articles, LinkOut, and other PubMed features. The recipient’s e-mail program must be set for HTML view in order to properly view in HTML format.
You can create a PubMed search as an RSS feed. An RSS reader is required to use this service. There are numerous RSS readers to choose from and many are available to download free from the Web.
To retrieve new items for your PubMed search since the last time you were connected to your RSS reader:
Run a search in PubMed.
Choose RSS Feed from the Send to menu.
On the RSS Feed Page you may edit the name of the feed and limit the number of items to be displayed, click Create Feed. If the number of citations retrieved is greater than your “limit” number you will have the option to link to PubMed to display the entire retrieval.
Click the XML icon to display the XML and copy and paste the URL into the subscribe form in your RSS reader. Web browsers and RSS readers may use different options to copy the feed.
PubMed RSS feeds use the My NCBI “What’s New” strategy for updating searches.
You can create a URL with your search terms that can be bookmarked in your Web browser for future use. Documentation is also available for creating a web link to PubMed.
Run a search and then click Details.
Click URL below the Query Translation box.
Bookmark the URL using your Web browser function. You can also copy the URL from the Web browser’s URL address box.
More information about creating a bookmark:
Searches that were created using a search statement number in History (e.g., #1 OR #2 AND human[mh]) can not be saved using the URL feature because search statements are lost when History expires. You may use History numbers to save a search in My NCBI.
After saving the bookmark, you may want to use your Web browser's edit functions to rename the bookmark.
My NCBI saves searches and results and features an option to automatically update and e-mail search results from your saved searches. My NCBI includes additional features for highlighting search terms, storing an e-mail address, filtering search results and setting LinkOut, document delivery service and outside tool preferences.
To access, click the My NCBI in the box that appears at the top right of the screen on all database pages.
Registering for My NCBI
Signing in and out of My NCBI
Forgot your My NCBI username or password
Changing your My NCBI password
Saving your searches & automatic e-mail updates
Running a saved search without update limits
Checking for new citations since you last updated a saved search
Deleting a search
Changing a saved search
Saving results in collections
Saving results in My Bibliography
Sharing My Bibliography
Deleting items in a collection
Managing your Recent Activity
Changing your filter preferences
Setting LinkOut preferences
Setting an outside tool preference
Setting your document delivery provider preference
Sharing filters, highlighting, document delivery, and outside tool settings
Click Register for an account on the My NCBI Sign In page.
Enter a username (3 or more alpha-numeric characters) and a password (6 or more alpha-numeric characters).
Choose a security question and answer so you can use it to reset your password if you forget it.
Enter the characters displayed as an image in the text box to help us prevent automated programs from registering accounts.
Record your username, password, and answer to the security question for future reference.
Usernames and passwords are case sensitive.
Only one email address may be associated with each My NCBI account.
A confirmation message will be sent to the email address to activate automatic email updates.
Enter your username and password and click Sign In. Click the Keep me signed in check box to create a permanent cookie so after you sign in, My NCBI will be indefinitely available from your computer without signing in again.
Click the Remember my name check box to retain your username on your computer.
Click Sign Out from the My NCBI header to sign out.
If the Keep me signed in check box is not checked your My NCBI account will be active for your current session only. You will be automatically signed out after you close your browser window.
You may sign out at any time to sever your access to My NCBI whether you sign in using the session-only option or automatic sign in.
Click login options for My NCBI partner organizations to log into My NCBI using another organization’s account.
If you forgot your username click I forgot my username on the Sign In page, enter your e-mail address, and then click Send Reminder.
If you forgot your password click I forgot my password on the Sign In page.
Enter your username and click Next.
Answer the security question you chose when you registered, or select Send an email to the address specified in my account.
After verification, you will be prompted to enter a new password.
Make a note of the new password, you will need it to Sign in to My NCBI.
Sign in to My NCBI.
Under Preferences click Common Preferences
Enter your old password and new password and click Save.
To save your searches and set up automatic e-mail updates:
Sign in to My NCBI.
Run or preview your search. You may use History numbers in your search, however, PubMed processes from left to right so order your search statement numbers with this in mind, or use parentheses for nesting.
Click the Save Search link next to the search box Go button.
You may edit the name of the search. The maximum number of characters for the search name is 100. The name of the saved search will be included in the Subject of the automatic e-mail update messages.
Fill in the Save Search Settings form if you would like to receive automatic e-mail updates of new search results.
Click the set an e-mail address link if you have not already saved one. This address will be used for all e-mail updates for the account.
Select the frequency of your updates. E-mailed updates will be sent daily on the scheduled days starting from the appropriate day after the schedule is set.
Set the Format to HTML or Text.
You may also change the report format, number of items to be sent, or add additional text (up to 200 characters) to the automatic updates.
To change or create a schedule for a saved search select My Saved Data, click the Saved Searches Manage link, and then click Edit for the saved search.
Links to Related Articles cannot be saved in My NCBI.
Dates and date ranges are not recommended for saved searches.
Saved searches cannot be edited.
If an e-mail update bounces back (cannot be delivered) three times, the e-mail address will be changed to invalid.
Each My NCBI account can only have one e-mail address.
In the event an update is not sent out on schedule or is incomplete, the next scheduled update will include the omitted items, if any.
E-mail updates may be affected by e-mail filtering SPAM software. Consider adding nih.gov domain to your e-mail "safe list."
Click the database searches’ column headings to sort alphabetically by name, last searched date, or schedule.
An initial e-mail message will be sent to confirm e-mail addresses used for My NCBI. Recipients must confirm their e-mail account before My NCBI will automatically send updates.
Sign in to My NCBI.
Under My Saved Data, click the saved search you want to run.
Note: This will not modify the Last Searched date and time for the saved search.
Sign in to My NCBI.
Under My Saved Data, click the Saved Searches Manage link.
The Last Searched column displays when the last update was generated either automatically or manually. Mouse over the information to display the explicit date.
Click the check box next to a search. To select all your searches click the check box under the database name.
Click Show What’s New.
To display the new items, click the # new items link. This also updates the saved search with the current date and time.
Note: If you do not click # new items, the search date and time are not updated.
More information about My NCBI updates:
My NCBI uses the following strategy, for searches with untagged terms and searches that do not use Limits, to find new citations:
(Search AND T1 : T2 [MHDA]) NOT (Search [TIAB] AND 0001 : T1 [EDAT])
Search = saved search.
T1 = the date and time the search was last updated.
T2 = today's date and time.
0001 = the date that will include all citations.
[MHDA] = the search tag for the MeSH date. This field reflects the date MeSH terms were added to the citation. (Note: until MeSH terms are added, the MHDA value is the same as the EDAT.)
[EDAT] = the search tag for the date the citation was added to PubMed.
[TIAB] = the search tag for words in the Title and Abstract fields.
|The saved search is heart attack. The search was last updated on January 7, 2008 at 11:00 a.m. and today's update date and time is January 13, 2008 9:59 a.m.|
|("myocardial infarction"[MeSH Terms] OR ("myocardial"[All Fields] AND "infarction"[All Fields]) OR "myocardial infarction"[All Fields] OR ("heart"[All Fields] AND "attack"[All Fields]) OR "heart attack"[All Fields]) AND "2008/01/07 11.00"[MHDA] : "2008/01/13 09.59"[MHDA]) NOT (heart attack[TIAB] OR |
("myocardial"[TIAB] AND "infarction"[TIAB]) OR "myocardial infarction"[TIAB] OR ("heart"[TIAB] AND "attack"[TIAB]) AND "0001"[EDAT] : "2008/01/07 11.00"[EDAT])
My NCBI "remembers" the date and time you last retrieved new items from your Saved Search(es). For strategies without search tags, it also considers whether citations that were in-process (not yet indexed) the last time you updated have since had MeSH terms applied, and are now retrieved by your strategy.
My NCBI saved searches that include search field tags or selection from the Limits page use an abbreviated what's new search to ensure that all citations are retrieved.
Searches that include the search field tags FAU, IR, 1AU, LASTAU, CN, AU, PS, IP, TA, LA, PG, TI, TIAB, LID, JID, TT or VI use the strategy: Search AND T1 : T2 [EDAT]
Searches that include search field tags other than the ones listed above, use the strategy: Search AND T1 : T2 [MHDA]
The My NCBI What’s New feature will not retrieve citations for articles that were published more than one year ago.
To retrieve all new citations regardless of publication date, do not use either the “e-mail updates” or “Show What’s New” options for My NCBI Saved Searches. Rather, run the saved search and combine it with a Create Date range (see Searching by Date).
Sign in to My NCBI.
Under My Saved Data, click the Saved Searches Manage link, and then click the check box for a search to select it.
Click Delete Searches.
Saved searches cannot be edited; save a new search with your changes and delete the old one.
To change a saved search:
Sign in to My NCBI.
Under My Saved Data; click the name of the saved search you want to edit.
The saved search will run in PubMed without any date limits, and the search will display in the search box.
Edit, change or correct the search and click Go to run the revised search.
Click the Save Search link next to search box and follow the steps to save the revised search.
Delete the old saved search.
To save results in a collection:
Sign in to My NCBI.
Run a PubMed search, on the results page select the items you want to save using the check boxes; if you do not select any items all results up to 5000 items will be sent to collections.
Select Collections under the Send to menu.
On the Save Collection window you may create a new collection or append to an existing collection, enter a collection name.
To share a collection:
In My NCBI under My Saved Data, click the Collections Manage link.
Click Private next to the collection you want to share.
Select the Public radio button.
Copy the Direct URL or HTML for Web Pages text.
To display your collections, under My NCBI My Saved Data, click the Collections Manage link.
Click the column headings to sort alphabetically by name, last modified date, or by the number of items in each collection.
Use the check boxes to select collections to delete and then click Delete PubMed Collections.
Click the collection name to display the items in PubMed.
Click Edit to view the collection contents, change the name, delete individual items, or display the citation in PubMed within a collection.
Under My Saved Data click the Collections Manage link.
Use the check boxes to select the collections you want to merge.
Click Merge PubMed Collections.
Under My Saved Data click the collections Manage link.
Click Edit for the collection name.
Use the check boxes to select items to delete.
Click Remove Selected from the Actions menu.
Recent Activity saves your searches and records viewed from the last 6 months.
To display your Recent Activity, under My Saved Data, click Recent Activity.
Click the search or record link to display an item’s contents in the specified database.
Use the check boxes to select items and then click the Actions bar menu icons to:
Create a Saved Search
Move to a Collection
Clear or Turn Recent Activity off
To change the sort from date/time to database, click the Sort by Application icon.
Enter a search in the Search Recent Activity box to search your saved activity items. Additional search criteria are available under the Additional Criteria link.
My Bibliography and Other Citations are available to save your PubMed citations using a search template.
To populate My Bibliography with your papers:
Under My Saved Data click My Bibliography.
Click add items if your bibliography is empty.
Enter your name and other optional search criteria to limit your search if your name is not a unique author name in PubMed, click Go.
Review the list of citations and use the check boxes to select your papers, click Add to My Bibliography.
To add additional citations since the last time you updated your bibliography click the plus symbol on the My Bibliography Actions bar.
Use the Other Citations link under My Saved Data to create an additional bibliography using a saved search form.
Click the View Results in PubMed icon to display your bibliography in PubMed.
To share your My Bibliography:
In My NCBI under My Saved Data, click the My Bibliography link.
Click the Edit Collection Settings link
Select the Public radio button.
Copy the Direct URL or HTML for Web Pages text.
The URL, or the link created by the HTML, displays the citations currently in the collection maintained by the user of the My NCBI account. Updating the collection does not require a change to the URL.
If a collection is changed back to Private, the URL is no longer valid. Click Save after making changes.
To store or change an e-mail address for the automatic e-mail updates and the Send to E-mail feature:
Sign in to My NCBI
Click Preferences on the My NCBI sidebar.
Click E-mail address.
A confirmation e-mail message will be sent to the e-mail address to activate automatic e-mail updates.
For the Send to E-mail option, you may enter a different address that will not affect your My NCBI updates.
To highlight search terms as well as terms that have been added by PubMed to enhance your search choose a highlight color under Preference Highlighting, and then click Save. Highlighting is only active when you are signed into My NCBI; the default user preference is set to Off.
The default display for single citations is AbstractPlus. For searches that retrieve multiple results and display in the Summary format, click the title to display the AbstractPlus format. To change the single citation default display choose a different format the Preferences Single Citation Display, and then click Save.
Note: You can also change the single citation display by adding a URL parameter to the PubMed URL. The parameter is dr= followed by the display name.
For example, to change the default to the MEDLINE display use:
My NCBI includes a filters feature that groups search results by areas of interest. Filter results with their respective counts for the current search display as tabs, next to the All tab for the total search retrieval. Click on the tab to display the citations grouped by that filter. You can have up to five active filters for each database.
To change your filter selections:
Sign in to My NCBI.
Click the tool icon to the right of the filter tabs to link to My Filters and display your active filters and icon settings.
Click the check boxes to select or deselect filters.
To view additional options click:
Frequently Requested Filters to display a selective list of popular filters.
Browse Filters to browse filters by category. Subject-related filters are under Properties.
Search for Filters to search the filter names and descriptions.
Click the Create New Custom Filter link.
Enter the Filter name you want to display for this filter.
Enter the filter search strategy in the Search box, click Run Filter.
Click Save Filter.
Click the check box next to the Filter name to activate the filter.
Your filter selections are in effect only when you are signed in to My NCBI.
Note: When you click on the filter tab a tack symbol will appear in the tab. Click the tack to append the filter to your search. Custom Filters cannot be appended to a search.
In PubMed, the icon to the citation provider is included on the AbstractPlus, Abstract and Citation displays. All other links to providers display on the LinkOut page.
To customize your LinkOut preferences:
Sign in to My NCBI.
Click Search Filters on the My NCBI sidebar.
Click PubMed to view your current list of filters..
To view or change your LinkOut icons settings click:
Browse Filters to browse filters and LinkOut providers by category.
Search for Filters to search the filter and LinkOut provider names and descriptions.
My Filters to see a list of your current filter and LinkOut provider icon settings.
Click the check box next to each selection to add an icon to your PubMed displays.
Note: Your LinkOut preferences are in effect only when you are signed in to My NCBI.
PubMed supports outside tool. Outside Tool allows institutions to display an icon link back to their institution on the AbstractPlus, Abstract and Citation format for all PubMed citations. The icon link is the base URL provided by the institution and the PMID of the citation. Please send questions about this service to firstname.lastname@example.org through or
To add an Outside Tool preference:
Sign in to My NCBI.
Choose Preferences, and under PubMed Preferences, click Outside Tool.
Select an institution from the list.
Your outside tool preference is in effect only when you are signed in to My NCBI.
Additionalinformation is available in the LinkOut Help.
NLM’s order documents feature.is the default document delivery provider for PubMed’s
To change your document delivery provider:
Sign in to My NCBI.
Choose Preferences, and under PubMed Preferences, click Document Delivery.
Select a service from the list.
Note: Your document delivery preference is in effect only when you are signed in to My NCBI.
My NCBI accounts can be configured to share filter, highlighting, document delivery, and outside tool settings.
To setup a shared account:
Sign in to My NCBI.
Click Preferences, and under Common Preferences, click Shared Settings.
Click the share selection box for each My NCBI feature. Only those settings for a feature where the share box is checked will be shared.
Create a URL using the following format:
where username is the shared My NCBI account Sign in name.
Use this URL to create a link to PubMed.
More information about My NCBI Shared Accounts:
Settings activated using a My NCBI shared account URL will timeout after eight hours of inactivity.
A user accessing PubMed using shared settings is not signed in to My NCBI so the My NCBI box will not display Welcome username.
If a user signs in to My NCBI the setting for their personal account will take precedent over the shared account settings.
PubMed does not include copies of journal articles. Here are some tips for obtaining articles.
Many articles are available for free.
If you are a physician, researcher, or health professional, utilize your affiliation with a medical library or institution.
Follow this link on PubMed citations to:
PubMed Central is a free digital archive of full-text journal articles maintained by the U.S. National Institutes of Health.
To access the article, click the Free article in PMC link to go to the abstract view, and then click the “Free full text article in PubMed Central” icon.
On the AbstractPlus view click the free full text article icon.
Direct from publisher as some publishers will provide free access to articles after you register as a guest.
Note: When you click a full text link in PubMed, you leave PubMed and are directed to the full text at an external provider's site. NLM/NCBI does not hold the copyright to this material, and cannot give permission for its use. Users should review all copyright restrictions set forth by the full text provider before reproducing, redistributing, or making commercial use of material accessed through LinkOut.
Please see thepage for additional information.
Your local medical library is your best option. If you see icons for your library on the abstract view this indicates that your library provides a link to the article, or has the journal in its collection.
Example library icons:
If your library does not have access to the article you need, ask a librarian about ordering the article from other institutions.
If you need articles on a routine basis consider using the PubMed Order option under the Send to menu.
First, you must register with a delivery service.
The default article order service in PubMed is the NLM-sponsoredservice. This allows you to order the full-text of an article from participating medical libraries. Local fees and delivery methods will vary. This service is recommended for health professionals associated with a medical library.
If you are not affiliated with a medical library or want to change your document delivery provider to another service use Document Delivery in My NCBI.
After registering for Loansome Doc or another document ordering service use the PubMed’s Send to Order feature to place the order:
Click the check box next to each citation to order. You may move to other pages within your results to select additional citations.
From the Send to menu, select Order.
Follow the on-screen directions.
Note: For information on the medical libraries in your area (or country) that provide articles viacheck the frequently asked questions ( ) including: How do I find an ?
Some local libraries have copies of medical journals or can get a copy of an article for you. Ask your local librarian about inter-library loan options and if there will be a charge.
For information on the medical libraries in your area (or country) that provide articles via the NLM-sponsoredservice check the frequently asked questions ( ) including: How do I find an ?
Journal publishers or related organizations may provide access to articles for a fee or sometimes free following your registration as an individual or guest. When available, icons to these sources can be found on the AbstractPlus, Asbstract and Citation displays.
Additional links to articles may be available on the LinkOut display.
Example abstract icons:
Searching by using the MeSH database
Searching for journals in the Journals database
Using the Text version of PubMed
Creating a Web link to search PubMed
Using the E-utilities programming tools
Using the Batch Citation Matcher
Using Batch Entrez
(Medical Subject Headings) is NLM's controlled vocabulary thesaurus used for indexing MEDLINE articles. The is available from the Search menu or the sidebar.
Use the MeSH database to find MeSH terms including Subheadings, Publication Types, Supplementary Concept Records (substance names) and Pharmacological Actions - and build a PubMed search strategy. The MeSH database can be searched by MeSH term, MeSH Entry Term, Subheading, Publication Type, Substance Name, or words within a MeSH Scope Note. Subheadings and Publication Types are included in the MeSH term searches.
Please see the following MeSH Database animated tutorials:
What are the Suggestions? The database displays MeSH or Entry Term suggestions based on anthat compares letter combinations in words. You can use the MeSH or Entry Term suggestion link to go directly to a record. A new set of suggestions will be displayed based on the selected term.
More information about the MeSH database:
Search results are displayed in relevance-ranked order, therefore, when a user’s search exactly matches a MeSH Term, that Term is displayed first.
Click the MeSH term from the Summary display or choose Full from the Display menu to view additional information and search specifications, such as Subheadings, Restrict Search to Major Topic headings only or Do Not Explode this term.
Year Introduced is the year the term was added to the MeSH. If more than one year is shown, the term was available for indexing back to the earliest year noted. Articles are indexed using the vocabulary in place at the time of indexing, therefore, the Year Introduced for a term and the date of publication of a citation indexed with that term may not agree.
The MeSH database Links menu includes the following links:
PubMed - retrieves citations for the MeSH term in PubMed.
PubMed – Major Topic – retrieves citations for the MeSH terms as a Major Topic of the article in PubMed.
Clinical Queries - enters the MeSH term in the Clinical Queries search box.
NLM MeSH Browser - links to the NLMfor more information about the MeSH term.
The display menu option PubMed Links retrieves PubMed citations for the selected MeSH terms or the MeSH terms displayed on the page.
Search Box: The MeSH database provides a Search Box that can be used to build a PubMed search. From any display format:
Click the MeSH term check box, including specifications if using the Full display, e.g., Subheadings.
Use the Send to menu to select one of the following:
Search Box with AND
Search Box with OR
Search Box with NOT
To add additional terms to this strategy, continue searching the database and add terms to the Search Box using the Send to Search Box feature.
When you have completed your search click Search PubMed.
Theincludes information about the journals in PubMed and the other NCBI databases.
What are the Suggestions? In addition to the search results, this database provides suggestions. The suggestions are based on anthat scores the relatedness of phrases included in a user's journal query. Click on a journal under Suggestions to go directly to a specific journal record. Suggestions are generated from an index (multi) that is a combination of indices which may result in a journal being repeated in the list of suggestions.
Searching in the Journals database:
Enter the full or partial journal name in the search box
Click the journal title for a specific journal, or choose Full from the Display menu, to view additional information.
Building a PubMed search for multiple journals:
Run a search and use the check boxes to select the journals.
Select Search box with OR from the Send to menu.
To add additional journals continue searching the database and adding the journals to the Search Box using the Send to Search Box feature, and then click Search PubMed.
Note: To search PubMed for all journals displayed in a journal search choose PubMed Links from the Display menu.
More information about the Journals database:
The Journals database includes journals in the other NCBI databases as well as PubMed. To limit journal searches to only PubMed journals or currently indexed MEDLINE journals, click these check boxes in Limits.
Click the NLM ID to link to journal information in the.
If a journal includes parentheses or brackets, e.g., J Hand Surg [Am], enter the abbreviation or title without the special characters, j hand surg am.
Search results are displayed in alphabetical order except when a user's search exactly matches a journal title, then that title will display first.
Untagged journal terms are searched in all fields. The following tags are also available to limit your search to a specific field:
Some or all of the journal issues are printed on acid-free paper. Search as acidfree.
The last year of the publication. To enter a date range, insert a colon (:) between each date, e.g., 1996:1998 [eyr].
Search for journals that are currently indexed for MEDLINE with currentlyindexed and those that are not currently indexed with notcurrrentlyindexed. Search for the version of the journal indexed as currentlyindexedprint or currentlyindexedelectronic.
Used for internal processing at NLM.
To search for an indexed for journal subset, enter in the search box jsubset?, where ? represents the subset value. Click the Limits tab to search for subsets.
Search for selectively or fully indexed journals as: currentindexingtreatmentfull or currentindexingtreatmentselective.
The International Organization for Standardization (ISO) journal abbreviation.
The ISSN number for the journal.
Search for all print or electronic ISSNs as print[is] or electronic[is].
The language the journal is published. Click the Limits tab to search by language.
The NLM Integrated Library System alpha-numeric identifier for the journal.
Indicates the journal's country of publication.
Search for journals currently in PubMed Central (PMC) as: journals pmc[sb] and for forthcoming PMC journals as: journalspmcforthcoming.
The first year of the publication. To enter a date range, insert a colon (:) between each date, e.g., 1996:1998 [syr].
Subject terms are assigned by NLM for MEDLINE journals to describe a journal’s overall scope. The complete list ofis available
To search for journals included in a specific database, enter journals xxx[sb], where xxx is the database, e.g., journals nuccore[sb]
The full journal title.
The journal title abbreviation.
Other journal resources include:
The list of PubMed journals with
Athat are included in PubMed by FTP in the Uncompressed GNU Zip, UNIX Compress, or PKZIP format
TheIndexed for Online Users
TheIndexed in Index Medicus
Clickon the PubMed sidebar.
The Text version is helpful for users who require special adaptive equipment to access the Web. It provides basic PubMed search and retrieval functionality.
The Text version will probably also work well with a handheld, mobile or personal digital assistance ( PDA). Additional NLM projects including access to PubMed using devices such as Palm Powered and Pocket PC handheld computers is available from thepage.
Text Versionis available.
are tools that provide access to data outside of the regular Web search interface. This may be helpful for retrieving search results for future use in another environment.
The, available from the PubMed sidebar menu, allows you to retrieve the PubMed IDs for many articles all at once. This feature requires that you enter the bibliographic information (journal, volume, page, etc.) in a format outlined in the Batch Citation Matcher online .
Useto upload a file of PMIDs directly to PubMed.
How PubMed works: automatic term mapping
MEDLINE display format
NLM author indexing policy
PubMed character conversions
Untagged terms that are entered in the search box are matched (in this order) against a(Medical Subject Headings) translation table, a Journals translation table, the Full Author translation table, Author index, the Full Investigator (Collaborator) translation table and an Investigator (Collaborator) index.
When a match is found for a term or phrase in a translation table the mapping process is complete and does not continue on to the next translation table.
The MeSH Translation Table contains:
The See-Reference mappings (also known as entry terms) for MeSH terms
Pharmacologic action terms
Terms derived from the Unified Medical Language System () that have equivalent synonyms or lexical variants in English
Supplementary concept (substance) names and their synonyms.
If a match is found in this translation table, the term will be searched as MeSH (that includes the MeSH term and any specific terms indented under that term in the), and in all fields.
For example, if you enter child rearing in the search box, PubMed will translate this search to: "child rearing"[MeSH Terms] OR ("child"[All Fields] AND "rearing"[All Fields]) OR "child rearing"[All Fields]
If you enter a MeSH Term that is also a Pharmacologic Action PubMed will search the term as [MeSH Terms], [Pharmacologic Action], OR in [All Fields].
If you enter an entry term for a MeSH term the translation will also include an all fields search for the MeSH term associated with the entry term. For example, a search for odontalgia will translate to: "toothache"[MeSH Terms] OR "toothache"[All Fields] OR "odontalgia"[All Fields] because Odontalgia is an entry term for the MeSH term toothache.
Substance name mappings do not include a mapping for individual terms in a phrase, e.g., IL-22 will not include IL[All Fields AND 22[All Fields].
MeSH term mappings that include a standalone number or single character do not include a mapping for individual terms in a phrase, e.g., Protein C will not include Protein[All Fields] or C[All Fields].
More information about automatic term mapping:
Click Details to verify how your terms are translated. If you want to report a translation that does not seem accurate for your search topic, please e-mail the information to the NLM.
The Journals translation table contains the:
full journal title
These will automatically map to the journal abbreviation that is used to search journals in PubMed and in all fields. For example, a search for endocrine pathology will translate to: "Endocr Pathol"[Journal] OR ("endocrine"[All Fields] AND "pathology"[All Fields]) OR "endocrine pathology"[All Fields]
The full author translation table includes full author names for articles published from 2002 forward, if available. Enter a full author name in natural or inverted order, e.g., julia s wong or wong julia s.
More information about full author searching:
A comma following the last name for searching is optional. For some names, however, it is necessary to distinguish which name is the last name by using the comma following the last name, e.g., james, ryan.
Omit periods after initials and put all suffixes at the end, e.g., vollmer charles jr
Initials and suffixes are not required, if you include a middle initial or suffix, you will only retrieve citations for articles that were published using the middle initial or suffix.
To distinguish author initials that may match a full author name use the [fau] search tag, e.g., peterson do[fau].
If the term is not found in the above tables, except for Full Author, and is not a single term, PubMed checks the author index for a match. When combining multiple authors, to avoid a match with full author names, include initials or use the [au] search tag, e.g., ryan[au] james[au].
The full investigator (collaborator) translation table includes full names, if available. Enter a full investigator name in natural or inverted order, e.g., harry janes or janes harry.
If the term is not found in the above tables, except for Full Author, and is not a single term, PubMed checks the investigator index for a match.
PubMed breaks apart the phrase and repeats the above automatic term mapping process until a match is found. PubMed ignores stopwords in searches.
If there is no match, the individual terms will be combined (ANDed) together and searched in all fields.
The National Library of Medicine cannot provide specific medical advice. NLM urges you to consult a qualified health care professional for answers to your medical questions. NLM does not have pamphlets or other materials to mail.
will direct you to information to help answer health questions. MedlinePlus brings together authoritative information from NLM, the National Institutes of Health (NIH), and other government agencies and health-related organizations. Preformulated searches are included in MedlinePlus and give easy access to medical journal articles. MedlinePlus also has extensive information about drugs, an illustrated medical encyclopedia, interactive patient tutorials, and latest health news.
Citations that carry the tag, [PubMed - in process] or [PubMed - as supplied by publisher] have not yet gone through NLM's quality control procedures and indexing process. It is during this process that errors are identified and corrected. It is not necessary to notify NLM of an error at this stage. However, if the error is still present when the above tags are no longer on the citation, please report it to the NLMand include the information below (or as much as possible).
The journal name, volume, issue, and page number.
The article title, or the PMID number (e.g., PMID: 1234567).
The correct name using the format, last name initials (e.g., Jones JA).
Your report will be forwarded to NLM's Quality Assurance for further investigation. If a change to the database is warranted, the citation will be corrected. Please understand that due to the large volume of requests we are unable to answer individual error reports.
NLM leases its data to vendors around the world. Other products and services will not necessarily immediately reflect corrections made to records at NLM. If you search MEDLINE through a vendor's system, please contact your vendor about their maintenance schedules.
The National Library of Medicine (NLM) displays the author's name as it appears in the article at the time of publication, only the last name plus the first two initials (e.g., Fauci AS) are used. If the author's name was printed incorrectly at the time of publication, then the journal in which the article appeared must publish an erratum before NLM will make the correction in MEDLINE. If this is the case, please contact the journal publisher.
It is NLM's policy that errata are acknowledged only if they are printed in a citable form; that is, an erratum notice must appear on a numbered page in the journal that originally published the article. Error notices that are inserted unbound into a journal issue or "tipped in" will not be considered part of the permanent bibliographic record. NLM does not make changes in the database in response to letters from authors or editors, unless such letters indicate that a substantive published erratum is forthcoming.
For additional information on how NLM handles errors, please review thefact sheet.
PubMed provides access to bibliographic information that includes MEDLINE, as well as:
The out-of-scope citations (e.g., articles on plate tectonics or astrophysics) from certain MEDLINE journals, primarily general science and chemistry journals, for which the life sciences articles are indexed for MEDLINE.
Citations that precede the date that a journal was selected for MEDLINE indexing.
Some additional life science journals that submit full text to PubMed Central and receive a qualitative review by NLM.
For additional information, please see the NLM Fact Sheet:
is the NLM's premier bibliographic database that contains references to journal articles in the life sciences with a concentration on biomedicine. A distinctive feature of MEDLINE is that the records are indexed with NLM's (MeSH). The database contains citations from , with some older material. New citations that have been indexed with MeSH terms, publication types, GenBank accession numbers, and other indexing data are available daily (Tuesday through Saturday) and display with the tag [PubMed - indexed for MEDLINE]. See also the .
In Process Citations
PubMed's in-process records provide basic citation information and abstracts before the citations are indexed with NLM's MeSH Terms and added to MEDLINE. New in-process records are available in PubMed daily (Tuesday through Saturday) and display with the tag [PubMed - in process].
Citations received electronically from publishers appear in PubMed with the tag [PubMed - as supplied by publisher]. New publisher supplied citations are available in PubMed Tuesday through Saturday. Most of these progress to "in-process" status and later to "indexed for MEDLINE" status. However, not all citations will be indexed for MEDLINE and therefore will retain either the tag [PubMed - as supplied by publisher] or [PubMed]. Publishers may submit citations for articles that appear on the Web in advance of the journal issue's release. These ahead-of-print citations also display the tag [Epub ahead of print].
A "cookie" is information stored by a Web site server on your computer. See thefor additional information.
In the case of PubMed, it is information about your interactions that may be needed later to perform a function. Cookies allow PubMed to provide more interactive features such as Preview/Index, Clipboard, History, My NCBI and paging through results. Cookies placed by PubMed are removed from your computer after a set time period unless you choose to use a persistent cookie with the My NCBI automatic sign in function.
To use these interactive features you need to enable cookies on your computer. Consult your browser's help for information on enabling cookies.
If you have problems using cookie-dependent features of PubMed, even after enabling cookies, possible reasons may include:
Cookies are blocked by your provider or institution. Check with your Internet provider and/or the system administrator at your institution to see if cookies can be accepted. Even if you have them enabled in your Web browser, if they are blocked by your provider or institution (e.g., by a firewall, proxy server, etc.), cookie-dependent features of PubMed won't work.
Your computer's date and time settings are incorrect. Check your computer's time settings to ensure that they are correct.
See the MeSH Subheadings and on the NLM website.
The MEDLINE Display Format tags table defines the data tags that compose the PubMed MEDLINE display format. The tags are presented in alphabetical order. Some of the tags (e.g., CIN) are not mandatory and therefore will not be found in every PubMed MEDLINE display format. Other tags (e.g., AU, MH, RN) may occur multiple times in one record. This format is available for exporting citations into a reference management software program.
Not all fields are searchable in PubMed. See Search Field Descriptions and Tags.
NLM's author indexing policy is as follows:
1966 - 1984: MEDLINE did not limit the number of authors.
1984 - 1995: The NLM limited the number of authors to 10, with "et al" as the eleventh occurrence.
1996 - 1999: The NLM increased the limit from 10 to 25. If there were more than 25 authors, the first 24 were listed, the last author was used as the 25th, and the twenty-sixth and beyond became "et al."
2000 - Present: MEDLINE does not limit the number of authors.
Until 1990, only five transliterated (Japanese and Cyrillic) authors were included on each citation. Since 1990, the first ten transliterated authors have been entered. Chinese ideograms for co-authors are not transliterated at all if the journal lists only a single transliterated name in the table of contents.
PubMed uses certain characters to have special meaning in searches, while others are converted to spaces, see PubMed.
Clinical Queries using Research Methodology Filters
|Category||Optimized For||Sensitive/ Specific||PubMed Equivalent|
|therapy||sensitive/broad||99%/70%||((clinical[Title/Abstract] AND trial[Title/Abstract]) OR clinical trials[MeSH Terms] OR clinical trial[Publication Type] OR random*[Title/Abstract] OR random allocation[MeSH Terms] OR therapeutic use[MeSH Subheading])|
|specific/narrow||93%/97%||(randomized controlled trial[Publication Type] OR (randomized[Title/Abstract] AND controlled[Title/Abstract] AND trial[Title/Abstract]))|
|diagnosis||sensitive/broad||98%/74%||(sensitiv*[Title/Abstract] OR sensitivity and specificity[MeSH Terms] OR diagnos*[Title/Abstract] OR diagnosis[MeSH:noexp] OR diagnostic * [MeSH:noexp] OR diagnosis,differential[MeSH:noexp] OR diagnosis[Subheading:noexp])|
|etiology||sensitive/broad||93%/63%||(risk*[Title/Abstract] OR risk*[MeSH:noexp] OR risk *[MeSH:noexp] OR cohort studies[MeSH Terms] OR group*[Text Word])|
|specific/narrow||51%/95%||((relative[Title/Abstract] AND risk*[Title/Abstract]) OR (relative risk[Text Word]) OR risks[Text Word] OR cohort studies[MeSH:noexp] OR (cohort[Title/Abstract] AND stud*[Title/Abstract]))|
|prognosis||sensitive/broad||90%/80%||(incidence[MeSH:noexp] OR mortality[MeSH Terms] OR follow up studies[MeSH:noexp] OR prognos*[Text Word] OR predict*[Text Word] OR course*[Text Word])|
|specific/narrow||52%/94%||(prognos*[Title/Abstract] OR (first[Title/Abstract] AND episode[Title/Abstract]) OR cohort[Title/Abstract])|
|clinical prediction guides||sensitive/broad||96%/79%||(predict*[tiab] OR predictive value of tests[mh] OR scor*[tiab] OR observ*[tiab] OR observer variation[mh])|
|specific/narrow||54%/99%||(validation[tiab] OR validate[tiab])|
The Clinical Queries search filters are based on the work of
Medical Genetics Search Filters
|Diagnosis||(Diagnosis AND Genetics)|
|Differential Diagnosis||(Differential Diagnosis[MeSH] OR Differential Diagnosis[Text Word] AND Genetics)|
|Clinical Description||(Natural History OR Mortality OR Phenotype OR Prevalence OR Penetrance AND Genetics)|
|Management||(therapy[Subheading] OR treatment[Text Word] OR treatment outcome OR investigational therapies AND Genetics)|
|Genetic Counseling||(Genetic Counseling OR Inheritance pattern AND genetics)|
|Molecular Genetics||(Medical Genetics OR genotype OR genetics[Subheading] AND genetics)|
|Genetic Testing||(DNA Mutational Analysis OR Laboratory techniques and procedures OR Genetic Markers OR diagnosis OR testing OR test OR screening OR mutagenicity tests OR genetic techniques OR molecular diagnostic techniques AND genetics)|
|All||((Diagnosis AND genetics) OR (Differential Diagnosis[MeSH] OR Differential Diagnosis[Text Word] AND genetics) OR (Natural History OR Mortality OR Phenotype OR Prevalence OR Penetrance AND genetics) OR (therapy[Subheading] OR treatment[Text Word] OR treatment outcome OR investigational therapies AND genetics) OR (Genetic Counseling OR Inheritance pattern AND genetics) OR (Medical Genetics OR genotype OR genetics[Subheading] AND genetics) OR (DNA Mutational Analysis OR Laboratory techniques and procedures OR Genetic Markers OR diagnosis OR testing OR test OR screening OR mutagenicity tests OR genetic techniques OR molecular diagnostic techniques AND genetics))|
The genetics searches were developed in conjunction with the staff of GeneReviews: Genetic Disease Online Reviews at GeneTests, University of Washington, Seattle.
The neighbors of a document are those documents in the database that are the most similar to it. The similarity between documents is measured by the words they have in common, with some adjustment for document lengths. To carry out such a program, one must first define what a word is. For us, a word is basically an unbroken string of letters and numerals with at least one letter of the alphabet in it. Words end at hyphens, spaces, new lines, and punctuation. A list of 132 common, but uninformative, words (also known as stopwords) are eliminated from processing at this stage. Next, a limited amount of stemming of words is done, but no thesaurus is used in processing. Words from the abstract of a document are classified as text words. Words from titles are also classified as text words, but words from titles are added in a second time to give them a small advantage in the local weighting scheme. MeSH terms are placed in a third category, and a MeSH term with a subheading qualifier is entered twice, once without the qualifier and once with it. If a MeSH term is starred (indicating a major concept in a document), the star is ignored. These three categories of words (or phrases in the case of MeSH) comprise the representation of a document. No other fields, such as Author or Journal, enter into the calculations.
Having obtained the set of terms that represent each document, the next step is to recognize that not all words are of equal value. Each time a word is used, it is assigned a numerical weight. This numerical weight is based on information that the computer can obtain by automatic processing. Automatic processing is important because the number of different terms that have to be assigned weights is close to two million for this system. The weight or value of a term is dependent on three types of information: 1) the number of different documents in the database that contain the term; 2) the number of times the term occurs in a particular document; and 3) the number of term occurrences in the document. The first of these pieces of information is used to produce a number called the global weight of the term. The global weight is used in weighting the term throughout the database. The second and third pieces of information pertain only to a particular document and are used to produce a number called the local weight of the term in that specific document. When a word occurs in two documents, its weight is computed as the product of the global weight times the two local weights (one pertaining to each of the documents).
The global weight of a term is greater for the less frequent terms. This is reasonable because the presence of a term that occurred in most of the documents would really tell one very little about a document. On the other hand, a term that occurred in only 100 documents of one million would be very helpful in limiting the set of documents of interest. A word that occurred in only 10 documents is likely to be even more informative and will receive an even higher weight.
The local weight of a term is the measure of its importance in a particular document. Generally, the more frequent a term is within a document, the more important it is in representing the content of that document. However, this relationship is saturating, i.e., as the frequency continues to go up, the importance of the word increases less rapidly and finally comes to a finite limit. In addition, we do not want a longer document to be considered more important just because it is longer; therefore, a length correction is applied. This local weight computation is based on the Poisson distribution and the formula can be found in.
The similarity between two documents is computed by adding up the weights (local wt1 × local wt2 × global wt) of all of the terms the two documents have in common. This provides an indication of how related two documents are. The resultant score is an example of a vector score. Vector scoring was originated by Gerard Salton and has a long history in text retrieval. The interested reader is referred to Salton, Automatic Text Processing, Reading, MA: Addison-Wesley, 1989 for further information on this topic. Our approach differs from other approaches in the way we calculate the local weights for the individual terms. Once the similarity score of a document in relation to each of the other documents in the database has been computed, that document's neighbors are identified as the most similar (highest scoring) documents found. These closely related documents are pre-computed for each document in PubMed so that when you select Related Articles, the system has only to retrieve this list. This enables a fast response time for such queries.