The Astrophysics Data System (ADS) is a NASA-funded project which maintains four bibliographic databases containing more than 3.6 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 the Abstract Service query forms, and full-text scans of much of the astronomical literature which can be browsed though the Browse interface. <b>Please note that all abstracts and articles in the ADS are copyrighted by the publisher, and their use is free for personal use only. For more information, please read ADS\' page detailing the Terms and Conditions regulating the use of the resources. </b> In addition to its databases, the ADS provides access and pointers to a wealth of external resources, including electronic articles, data catalogs and archives, and currently have links to over 4.6 million records maintained by the collaborators.