ADAMS (Agencywide Documents Access and Management System) provides access to image and text documents that the Nuclear Regulatory Commission (NRC) has made public since November 1, 1999, as well as bibliographic records (some with abstracts and full text) for earlier documents dating back to 1980.
NTRS provides access to NASA's current and historical technical literature and engineering results. Includes conference papers, journal articles, meeting papers, patents, research reports, images, movies, and technical videos.
"Science.gov searches over 60 databases and over 2200 selected websites from 15 federal agencies, offering 200 million pages of authoritative U.S. government science information including research and development results."
"ScienceResearch.com is a free, publicly available deep web search engine that uses advanced "federated search technology" to return high quality results by submitting your search query - in real-time - to other well respected search engines then collating, ranking and dropping duplicates of the results."