You can search Dissertations and Theses Full Text like many other databases.
After your first search, it can be helpful to use the options on the left side of the screen under Narrow Results.
It can be useful to limit to full text in the Dissertations and Theses database.
Dissertations can be a great resource!
While they are not peer-reviewed, they tend to be long documents with extensive reference lists. You can use these reference lists to help identify resources like books or articles that you can use in your research.