This is an online index of dissertations awarded from accredited academic institutions from 1861 through present day. The index selectively covers masters, Canadian dissertations, and European dissertations. New records are added monthly. Dissertation have gone through vigorous quality control and contain very detailed research on their topic. They often represent unique research that is not available elsewhere.
Dissertations are also very useful for their extensive bibliographies.
To find out if a dissertation was later published and is easily available, check the OPAC and WorldCat by author. Request the dissertation through Interlibrary Loan. Do be aware that this request my take longer than the average article request. The OPAC is the Online Public Access Catalog. It lists everything that this library owns.