Aachen
University Library of RWTH Aachen [free of charge]
Düsseldorf
University and State Library Düsseldorf (HHU) [15€ / year]
Cologne
University and City Library Cologne (UOC) [20€ / year, refundable]
University Library of TH Cologne [free of charge]
Mainz
University Library Mainz (JGU) [15€ / year, refundable]
Wuppertal
University Library Wuppertal (BUW) [free of charge]
Potsdam
University Library Potsdam (UOP) [free of charge]