ProQuest Dissertations & Theses Global
Its coverage of the USA and Canada is comprehensive, including masters' as well as doctoral theses. 1861-
A 24- page preview is available in full-text for some dissertations published after 1997. Includes open access dissertations and theses free of charge.
Coverage of other countries is less thorough, but there are records from individual universities in places as far apart as the Czech Republic, Australia, Thailand, Saudi Arabia and Germany. Coverage of US theses goes back to 1861, US and Canadian theses usually have an abstract.