1. German National Library of Science and Technology (TIB), Hannover, Germany
2. The British Library, London, UK
3. ETH Library Zurich, Zurich, Switzerland
4. Institute for Scientific and Technical Information (INIST)-CNRS, Vandoeuvre les Nancy, France
5. TU Delft Library, Delft, The Netherlands
6. Technical Information Center of Denmark, Lyngby, Denmark