Includes Science Citation Index Expanded (1900-present), Conference Proceedings Citation Index- Science (1990-present), Data Citation Index (1900-present), Current Chemical Reactions (1985-present), Index Chemicus (1993-present), BIOSIS Citation Index (1926-present), Derwent Innovations Index (1963-present), MEDLINE® (1950-present), and more.
Started in August 1991, arXiv.org is an electronic archive and distribution server for research articles. Covered areas include physics, mathematics, computer science, nonlinear sciences, quantitative biology, quantitative finance, statistics, electrical engineering and systems science, and economics.
Indexes major astronomy and astrophysics journals. 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.