Networked Digital Library of Thesis and Dissertations (NDLTD): :   http://www.ndltd.org/

OATD (Open Access Thesis and Dissertations): :   https://oatd.org/

American Doctoral Dissertations, 1933-1955:   www.opendissertations.com/

Biblioteca Digital de Teses e Dissertacoes da USP: www.teses.usp.br  

Deutsche Nationalbibnliothek- Dissonline:   www.dnb.de/EN/Wir/Kooperation/_node.html

British Library EThOS - Search and order theses online:   ethos.bl.uk

NARCIS:  www.narcis.nl

South African National ETD Portal:   www.netd.ac.za/

Library and Archives Canada:   www.bac-lac.gc.ca/eng/services/theses/Pages/theses-canada.aspx

RCAAP:  https://www.rcaap.pt/