Dissertations and theses are a valuable source for finding the latest research, sometimes even before it's been published in an article.  The major database for finding this material is in ProQuests's Dissertations and Theses Global.  Coverage goes back to 1861.  The database does not provide full text but does give a detailed abstract and a 24 page preview.

One drawback to using dissertations and theses is that due to copyright restrictions, it may be difficult to obtain a copy of one without buying it outright.

Before you resort to purchasing, first check ProQuest Dissertations & Theses Global.  This database of dissertations and theses provides a link to the full text that may be downloaded for free.

Another option is to request a copy through InterLibrary Loan  Some libraries will loan a copy but many libraries will not.  Still, it doesn't hurt to try.

If these options fail, Dissertations and Theses also has an "order a copy" feature.  Copies may be purchased in paper and microfilm formats and also as files for downloading.