Department of Energy's E-print Network
"A vast, integrated network of electronic scientific and technical information created by scientists and research engineers active in their respective fields, all full-text searchable."
NASA Technical Reports Server
Provides links to technical reports from many U.S. government laboratories involved with space research, e.g. Ames Research Center, Los Alamos, Jet Propulsion Laboratory, etc.
Science.gov
"Science.gov searches over 36 databases and 1,850 selected websites, offering 200 million pages of authoritative U.S. government science information, including research and development results." Includes government publications on astronomy and aerospace topics.
Science Accelerator
Science Accelerator searches important information resources from the U.S. Department of Energy. These resources contain the results of DOE research and development projects and programs, descriptions of R&D projects under way or recently completed, major R&D accomplishments, and recent research of interest to DOE. Includes bibliographic citations of DOE documents from 1948 to the present, with links to electronic full text when available.