Google Scholar can be a useful searching tool, particularly when it checks against the electronic full text holdings at FSU. This link requires you to log in with your FSU e-mail information-- but it's worth it!
Covers every doctoral dissertation completed in the U.S. at accredited institutions for the last 150 years. Includes some master's theses and foreign language dissertations. The full text of dissertations published since 1997 are available in PDF.