The Institute of Physics (IoP), Science Direct (Elsivier), and The American Institute of Physics (AIP) are the three main online portals for physics journals.
Institute of Physics (IoP)

The core of the journal publishing program for IoP is the Journals of Physics series, covering the key sub-disciplines of physics. In all, there are 34 established journals in all branches of pure and applied physics and 6 magazines including the internationally acclaimed Physics World, reflecting the growth and interdisciplinary nature of scientific research and application. For each journal, IoP gives a description of the journal's scope and offers very user friendly indexing and search options to find just the article you are looking for. A complete list by subject of IoP titles can be found here: IoP Journals.
Science Direct (Elsevier)
Science Direct by Elsevier has the most journal titles in physics available online. Like IoP, Science Direct offers a comprehensive list of journals which can be found here: Science Direct Physics Journals. By clicking on Physics and Astronomy you will find a list of physics journals by sub category.
American Institute of Physics (AIP)

The American Institute of Physics not only makes the journals they publish available through their site, but also provides access to over 100 titles from 18 other publishers. A complete alphabetical list of the resources available through the American Institute of Physics can be found at: American Institute of Physics.
Institute of Physics, Science Direct, and the American Institute of Physics are not the only collections of physics journals available for research. Some other important physics titles can be found at:
In many cases you will see links to full-text in your search results. If the full-text is not available, you should search the Library Catalog to see if the University owns the print version of the journal.