Physics and Astronomy
  • The Institute of Physics' Guide to Physics on the Web
  • news, views and information for the global physics community from IOP Publishing
  • Physical Review X APS's online-only, fully open access journal. Peer-reviewed journal that aims to publish from all areas of pure, applied, and interdisciplinary physics.
  • PhET PhET provides interactive, research-based simulations of physical phenomena for free
  • Space Telescope Science Institute (STScI) Preprints
  • Fermilab Preprints Server High-Energy Physics preprints from the Fermilab
  • IOP Science Latest Papers many of these are available freely for the first 30 days post publication
  • Mathematical Physics PrePrint Archive 
  • SAO/NASA Astrophysics Data System A Digital Library portal for researchers in Astronomy and Physics. The ADS maintains three bibliographic databases: Astronomy and Astrophysics, Physics, and arXiv e-prints. The main body of data in the ADS consists of bibliographic records, which are searchable through highly customizable query forms, and full-text scans of much of the astronomical literature which can be browsed or searched via full-text search interface
This is a subpage of the Physics, Chemistry, Astronomy, Math page, which you should also consult.