Smithsonian/NASA Astrophysics Data System (ADS)
ADS maintains four bibliographic databases containing more than 4.0 million records: Astronomy and Astrophysics, Instrumentation, Physics and Geophysics, and preprints in Astronomy. The main body of data in the ADS consists of bibliographic records, which are searchable through Abstract Service query forms, and full-text scans of much of the astronomical literature which can be browsed though the Browse interface.