arXiv.org e-Print Archive Started in Aug 1991, arXiv.org (formerly xxx.lanl.gov) is a fully automated electronic archive and distribution server for research papers. Covered areas include physics and related disciplines, mathematics, nonlinear sciences, computational linguistics, and neuroscience.
Astrophysical Data System (ADS) The Astrophysics Data System (ADS) is a NASA-funded project which maintains four bibliographic databases containing more than 4.2 million records: Astronomy and Astrophysics, Instrumentation, Physics and Geophysics, and preprints in Astronomy.
NASA Technical Reports Server (NTRS) Search databases from one or several NASA laboratories and space centers, including RECON, NACA reports, and the Astrophysics Data System. Includes citations to literature as far back as 1915.
Science.gov Science.gov is a gateway to authoritative selected science information provided by U.S. Government agencies, including research and development results.