Columbia Libraries has launched Academic Commons, a re-designed version of the earlier Digital Commons. The site
“collects, preserves, and makes accessible the scholarship and research of the faculty, staff, and students of Columbia University. The Commons will include articles and monographs, working papers, preprints, technical reports, conference papers, datasets, multimedia creations, and other materials in various digital formats. Content will grow as new communities and collections are added to Academic Commons.”
The site includes links to Columbia dissertations and theses, with full text in many cases. It is possible to browse these by academic dept., by navigating from Browse All Content By >>> Communities/Collections >>> Columbia Dissertations and Theses >>> Dissertations by Dept. (or follow this link).
Coverage for dissertations is from 1997 forward, with some selected content prior to 1997.
Remember also that for dissertations in general, Proquest Digital Dissertations, available through the Columbia Libraries, is a great resource (note: access limited to full-time students, faculty and staff).