In the same way you can use subject headings to find more books on a specific topic, you can use subject headings within databases to find similar scholarly articles. Subject headings (also called controlled vocabulary) differ from database to database.
The University Library owns only a few dissertations completed by students at other universities (an exception is the Herskovits Library of African Studies which purchases extensively within African studies). Those that are available can be found in NUsearch.
More and more universities are providing free online access to their dissertations and theses. If you know the university where the dissertation or thesis was completed, check their library catalog to see if a free digital copy is available. There are also some consortial efforts to provide open access dissertations and theses. Some examples include: