Access to Physical Review journals, including PROLA, the Physical Review Online Archive (contains all of Physical Review back to 1893, all of Physical Review Letters back to 1958, and all of Reviews of Modern Physics back to 1929).
ScienceDirect is a leading full-text scientific database offering journal articles and book chapters from more than 2,500 peer-reviewed journals and more than 11,000 books. Coverage goes as far back as 1823. Content areas include Physical Sciences, Engineering, Life Sciences, Health Sciences, Social Sciences, and Humanities.
Wolfram Alpha is a computational knowledge engine. It is not a search engine; rather, it generates output by doing computations from its own internal knowledge base. The best way to get an idea of its scope and capabilities is to view its Physics Examples page.