If you have a reference to a specific dissertation or thesis, you can look it up (by title and/or author) in the database Proquest Dissertations and Theses. This database has the full text of many dissertations and theses, especially those published in 1997 or later (although some earlier ones also have full text included).
You can also search for dissertations and theses by topic in Proquest Dissertations and Theses.
If the full text is not provided, you can request it through Interlibrary Loan.