SAO/NASA Astrophysics Data System (ADS)
http://adswww.harvard.edu/

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 9.5 million records: Astronomy and Astrophysics, Physics, and arXiv e-prints. The main body of data in the ADS consists of bibliographic records, which are searchable through highly customizable query forms, and full-text scans of much of the astronomical literature which can be browsed or searched via their 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. They currently have links to over 9.0 million records maintained by their collaborators. This has been added to Astronomy Resources Subject Tracer™ Information Blog. This will be added to Academic and Scholar Search Engines and Sources White Paper. This will be added to Deep Web Research Subject Tracer™.