This scholarly literature database provides abstracts and links to a wide variety of papers in astronomy and physics. It is maintained by NASA and the High Energy Astrophysics Division at the Harvard-Smithsonian Center for Astrophysics. Includes the option to set up a notification service (http://myads.harvard.edu/) to receive weekly updates on topics of interest to you.
This US federal government website contains search tools for many subjects of interest to the Department of Energy. This type of information was previously provided on the Department of Energy's Office of Scientific and Technical Information (OSTI) Information Bridge and the Energy Citations Database.
Search for thousands of technical documents from the European Organization for Nuclear Research, also known as Conseil Européen pour la Recherche Nucléaire (CERN: http://home.web.cern.ch/about). CERN provides researchers access to particle accelerators such as the Antiproton Decelerator, Large Hadron Collider and many others in order to study the fundamental components of matter and the structure of the universe.
The United States Naval Observatory (USNO) provides a wide range of astronomical data and products, and serves as the official source of time for the U.S. Department of Defense and a standard of time for the entire United States.