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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 14 million records covering publications in astronomy and astrophysics, physics, and the arXiv e-prints. Abstracts and full-text of major astronomy and physics publications are indexed and searchable. ADS also tracks also citations and usage of its records to provide advanced discovery and evaluation capabilities and provides access and pointers to a wealth of external resources, including articles available from publisher's websites, astronomical object information, data catalogs and data sets hosted by external archives.
