Preprint servers have an important role in Physics as repositories and gateways for communication, distribution and discussion of research results.
It's not just journal articles. Primary literature, the discussion of original research, is also found in preprint (pre-publication) articles (now often called e-prints), technical reports, conference and meeting papers, as well as dissertations. Besides the various resources shown on this page, INSPEC, Scopus and SciFinder searches can help here.
In addition to the links shown here, technical reports are searchable through most of the major scientific databases for physics, including INSPEC and SciFinder Scholar.