The University Library owns only a few dissertations completed by students at other universities (an exception is the Africana Collection which purchases extensively within African studies). Those that are available can be found in NUcat.
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:
If you would like to view a dissertation from another university, you can place an Interlibrary Loan request to see if a copy can be borrowed.