aeXiv Electrical Engineering and Systems Science
An open access repository of electronic preprints approved for posting after moderation, but not full peer review. It consists of scientific papers in the fields of mathematics, physics, astronomy, electrical engineering, computer science, etc. In many fields of mathematics and physics, almost all scientific papers are self-archived on the arXiv repository.
NTRS: NASA Technical Reports Server
Provides access to NASA's technical literature, literature from the National Advisory Committee for Aeronautics (NACA), the NASA Image Exchange, etc.
The primary search tool for Department of Energy (DOE) funded science, technology, and engineering research and development (R&D) results and the organizational hub for information about the DOE Office of Scientific and Technical Information (OSTI).