NASA Astrophysics Data System

TheĀ NASA Astrophysics Data Systems (ADS) is is a digital library portal for researchers in astronomy and physics with three bibliographic databases containing more than 9.7 million records: Astronomy and Astrophysics, Physics, and arXiv e-prints. There are also full-text scans of much of the astronomical literature which can be browsed or searched via a full-text search interface. Integrated in its databases, the ADS provides access and pointers to a wealth of external resources, including electronic articles, data catalogs and archives.