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.
Contains one-third of the world’s current literature in electrical engineering, communications, and computing. IEL provides researchers, engineers, and students access to over 1.2 million articles from 203 highly-cited IEEE journals, magazines, and transactions, more than 4 million conference papers from as far back as 1936, and approximately 4,900 IEEE standards documents in key technology fields.
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. 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.