Dissertations are distributed across various search platforms, so you may need multiple tools to perform comprehensive searches.
Open Access Theses and Dissertations -- OATD.org aims to be the best possible resource for finding open access graduate theses and dissertations published around the world. Metadata (information about the theses) comes from over 800 colleges, universities, and research institutions.
PQDT Open—a database providing access only to Open Access dissertations and theses in different disciplines.
Networked Digital Library of Theses and Dissertations—a national open-source tool (American Doctoral Dissertations via EBSCOhost).
American Doctoral Dissertations, 1902-present. - includes more than 153,000 theses and dissertations in total, and will include a link to access the full text, when available, via an Institutional Repository.
Google Scholar—include the following in your search dissertation site:edu You can limit the results by year.
OAIster database—a search tool that includes materials from various university Institutional Repositories.
FIND CITATION INFORMATION—and request a copy to be delivered.