Graduate student theses and dissertations are a form of grey literature commonly included in systematic reviews, because they represent academic research not (yet) published in academic journals and books. Theses and dissertations are often published open access on the university’s institutional repository. Below are some search portals that index theses and dissertations from many sources.
Networked Digital Library of Theses and Dissertations (NTLTD): NTLTD’s Global Electronic Theses and Dissertations Search indexes nearly six million theses and dissertations in NDLTD’s archive. Their Thesis Resources page also lists thesis and dissertation portals from over 35 countries, plus some other international sources.
Open Access Theses and Dissertations (OATD): The OATD Portal is international in scope, and indexes over five million theses and dissertations from over 1,100 universities and colleges
DART-Europe: DART-Europe is the European working group of NTLTD. The DART-Europe Thesis Portal indexes over 800,000 open access theses from 28 European countries