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 13 million records covering publications in Astronomy and Astrophysics, Physics, and the arXiv e-prints.
Scopus indexes content from 24,600 active journal titles and 5,000 publishers and generates precise citation results, detailed researcher profiles, and other useful data. The resource includes peer-reviewed literature from scientific, technical, medical, and social science (including arts and humanities) journals, books and conference proceedings.
Contains the three citation indexes that have existed since the early 1960s: Arts & Humanities, Science and Social Science Citation Index. Web of Science also tracks citations in Medline, newer sources and publications in Korea and Russia.