NEW ARTS & SCIENCES DISSERTATIONS & THESES
OLDER PSYCHOLOGY DISSERTATIONS & THESES (2014 and later)
ProQuest Dissertations and Theses A&I indexes 2.7 million thesis and dissertations from 1861 to the present day and includes 1.2 million that are full-text PDFs.
WorldCat is an international repository of library records. Because many libraries catalog their graduate students' dissertations and theses, there are many such items that are findable in WorldCat.
With many academic institutions creating institutional repositories (repositories of the scholarly work done by an institution's faculty and students), many dissertations and theses are searchable via the open web and can be found using Google Scholar.