SAO/NASA Astrophysics Data System

The SAO/NASA Astrophysics Data System (ADS) is a Digital Library portal for researchers in Astronomy and Physics, operated by the Smithsonian Astrophysical Observatory (SAO) under a NASA grant. The ADS maintains three bibliographic databases containing more than 8.9 million records: Astronomy and Astrophysics, Physics, and arXiv e-prints. 

See also: search, literature