By now there are many search engines for theses and dissertations. The latest is the NDLTD
http://www.ndltd.org/
From the home page, one has the choice of two engines:
"A comprehensive scientific research tool from Elsevier, Scirus ETD Search provides an advanced search that can narrow results to theses and dissertations as well as provide access to related scholarly resources."
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This is a dynamic search and discovery platform with sophisticated functionality. You can sort by relevance, title, and date. In the current implementation, faceted searches are available by language, continent, country, date, format and source institution. Additional facets, such as subjects or departments, can be added if desired."
A search of both engines found my doctoral dissertation, but neither had my master's theses (US thesis or UK thesis). VTLS listed the dissertation, with option to purchase. SCIRUS gives the impression that the dissertation was completed in 1970 (bold font) rather than 2005 (the latter is in regular font). Clicking the link gives further information, i.e. bibliographical details of the dissertation as well as its subsequent publication. The catch is that the categories are in French, but if you can't make it out there's a button that translates it into English.
The website gives URLs to other search engines.