Dissertations are book-length scholarly works submitted for completion of the Ph.D. They aren't "published" in the same sense as books and articles, but can be useful tools for identifying new scholarship and bibliographies. Theses in the U.S. are typically submitted for completion of a Masters degree, although terminology differs by country.
Index to doctoral dissertations from 1637 to the present, with abstracts since 1980. A number of master's theses are also indexed, with abstracts since 1988. Many are available for download in pdf format. UCLA has access to all full text dissertations in the database. Non-UCLA users may use Dissertations Express to purchase digital or print copies of individual dissertations.