Index of articles from over 10,000 journals in the sciences, social sciences, arts, and humanities. In addition to multidisciplinary searches, Web of Science provides tools to track citations to individual articles from their date of publication to the present. Now includes Book Citation Index and Conference Proceedings Citation Index. Coverage: 1900-present.
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 collections containing more than 15 million records covering publications in astronomy and astrophysics, physics, and general science, including all arXiv e-prints.