ProQuest Dissertations and Theses is a database of Ph.D. dissertations and Master's theses from the US and Canada. To access it, click on the dark blue "Databases" button on the library's home page and type "digital dissertations" in the search box, or click on the "A-Z List of Databases". Here is the direct link:
Rice dissertations in print, prior to 2012, when print ceased as a requirement for graduation, are located in the Library Service Center (LSC). To see a listing of all Rice dissertations, go to https://library.rice.edu and search with your terms. You will be able to limit to dissertations with the left-side option of "dissertations."