Nature journals offer Advance Online Publication (AOP).

We believe that AOP is the best and quickest way to publish high-quality, peer-reviewed research for the benefit of readers and authors. All papers published AOP, for any NPG journal, are the definitive version: they do not change before appearing in print and can be referenced formally as soon as they appear on the journal's AOP website.

Each journal's website includes an AOP table of contents, in which papers are listed in order of publication date (beginning with the most recent). Each paper carries a digital object identifier (DOI), which serves as a unique electronic identification tag for that paper. As soon as the issue containing the paper is printed, papers will be removed from the AOP table of contents, assigned a page number and transferred to that issue's table of contents on the website. The DOI remains attached to the paper to provide a persistent identifier.

Nature publishes some, but not all, papers AOP.

For the monthly Nature journals publishing primary research, new articles are uploaded to the AOP section of their web sites once each week. Occasionally, an article may be uploaded on other days.

About the AOP programme of the Nature Review journals.

About the AOP Practice Points published by the Nature Clinical Practice journals.

Q. Which articles are published AOP?

A. Original research is published AOP — that is, Articles and Letters, and for the Nature journals that publish them, Brief Communications. Occasionally, an associated News and Views is published with the AOP Article or Letter. More often, associated News and Views articles are not published until the papers are published in the print/online edition of the journal.

Q. Is the AOP version of the article definitive?

A. Yes. Only the final version of the paper is published AOP, exactly as it will be published in the printed edition. The paper is thus complete in every respect except that instead of having a volume/issue/page number, it has a DOI (digital object identifier). This means that the paper can be referenced as soon as it appears on the AOP site by using the DOI.

Q. What is a Digital Object Identifier?

A. The DOI is an international, public, "persistent identifier of intellectual property entities" in the form of a combination of numbers and letters. For NPG journals, the DOI is assigned to an item of editorial content, providing a unique and persistent identifier for that item. The DOI system is administered by the International DOI Foundation, a not-for-profit organization. CrossRef, another not-for-profit organization, uses the DOI as a reference linking standard, enables cross-publisher linking, and maintains the lookup system for DOIs. NPG is a member of CrossRef.

Q. What do the numbers in the DOI signify?

A. The DOI has two components, a prefix (before the slash) and a suffix (after the slash). The prefix is a DOI resolver server identifer (10) and a unique identifier assigned to the publisher—for example, the identifier for NPG is 1038 and the entire DOI prefix for an article published by NPG is 10.1038. The suffix is an arbitrary number provided by the publisher. It can be composed of numbers and/or letters and does not necessarily have any systematic significance. Each DOI is registered in a central resolution database that associates it with one or more corresponding web locations (URLs). For example, the DOI 10.1038/ng571 connects to http://dx.doi.org/10.1038/ng571.

Q. Can I use the DOI in a reference citation?

A. Yes, instead of giving the volume and page number, you can give the paper's DOI at the end of the citation. For example, Nature papers should be cited in the form;

Author(s) Nature advance online publication, day month year (DOI 10.1038/natureXXX).

After print publication, you should give the DOI as well as the print citation, to enable readers to find the paper in print as well as online. For example;

Author(s) Nature volume, page (year); advance online publication, day month year (DOI 10.1038/natureXXX).

Q. How can I use a DOI to find a paper?

A. There are two ways:

1. DOIs from other articles can be embedded into the linking coding of an article's reference section. In Nature journals these appear as "|Article|" in the reference sections. When |Article| is clicked, it opens another browser window leading to the entrance page (often the abstract) for another article. Depending on the source of the article, this page can be on the NPG's site or a site of another publisher. This service is enabled by CrossRef.
2. A DOI can be inserted directly into the browser. For example, for the DOI 10.1038/ng571, typing http://dx.doi.org/10.1038/ng571 brings up the entrance page of the article.

Q. What is the official publication date?

A. Many journals, and most abstracting and indexing services (including Medline and ISI) cite the print date as the publication date. Publishers are increasingly stating both the 'online publication date' and the 'print publication date'. NPG publishes both dates for our own papers, in the hope that scientific communities, as well as abstracting and indexing services, will recognize these dates.

We endeavour to include both the online publication date and the usual print citation in reference lists of NPG papers, where a paper has been published online before being published in print. Given the use of the DOI in locating an online publication in the future, we encourage authors to use DOIs in reference citations.

For legal purposes (for example, establishing intellectual property rights), we assume that online publication constitutes public disclosure. But this is for the courts to decide; NPG's role as a publisher is to provide clear documentation of the publication history, online and in print.

Q. Must I be a subscriber to read AOP articles?

A. Yes. AOP papers are the same as those in the print/online issues: while abstracts are freely available on any NPG journal's web site, access to the full-text article requires a paid subscription or a site license.

Q. Does Medline use DOIs?

A. Medline currently captures DOIs with online publication dates in its records, and is developing an enhanced level of support for the DOI system.

Q. Does Thomson-Reuters use DOIs?

A. Thomson Reuters captures DOIs in its records at the same time as the volume/issue/page number. Therefore, it is not using the DOI to capture information before print publication, but rather as an additional piece of metadata.

Q. How does AOP affect the Impact Factor?

A. Impact factors are calculated by Thomson-Reuters. At present, Thomson-Reuters bases its calculations on the date of print publication alone, so until or unless it changes its policy, AOP has no effect on impact factors.

Q. What are the page numbers in PDFs of AOP papers?

A. For convenience, the PDF version of every AOP article is given a temporary pagination, beginning with page 1. This is unrelated to the final pagination in the printed article.