NASA ADS 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 11.7 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 fully searchable searchable through the new ADS interface as well as the more traditional "Classic" search forms.
See also Historical Scans Currently in the ADS for Observatory publications, observations, bulletins, and circulars, including the Annals of the Harvard College Observatory (1852-1945) and the Annals of the Astrophysical Observatory of the Smithsonian Institution (1900-1954).
Web of Science Indexes the journal literature of the sciences from 1940 to the present; includes cited reference search capability. The Web of Science is part of the Web of Knowledge suite of database offerings.
The HOLLIS Catalog is a database containing records for millions of books, journals, manuscripts, government documents, maps, microforms, music scores, sound recordings, visual materials, dissertations, and data files in libraries at Harvard
Google Scholar enables you to search for scholarly literature, including peer-reviewed papers, theses, books, preprints, abstracts and technical reports from all broad areas of research.
WorldCat FirstSearch OCLC connects you to the collections and services of more than 10,000 libraries worldwide.
Encyclopedia of Astronomy and Astrophysics includes the full text of over 2,750 articles, plus sophisticated search and retrieval functionality, links to the primary literature, and is frequently updated with new material.