- 2001-present: Honorary Professor at Henan Normal University (Xinxiang, China)
- 2009-present: Honorary Director and Special Fellow of WISE Lab (Webometrics, Informetrics, Scientometrics, Econometrics Laboratory) at the Dalian University of Technology, Dalian, China and 2005-2009, Director (together with Liu Zeyuan) of WISE Lab
- 2004 – 2009: “Sea-sky Scholar” and Special Engaged Professor at the Dalian University of Technology, China
- 2000-present: Head of the COLLNET-Center, Hohen Neuendorf, Germany
- 2011 - 2012: Research Associate, Technical University Wildau, Germany
- 2005-2006: Research Associate, Institute of Library and Information Science, Humboldt-University of Berlin, Germany
- 2002-2005: Research Associate, Nerdi, NIWI-KNAW, Amsterdam, The Netherlands
- 1996-present: Private Lecturer (PD), Germany
- Apr./May 2002: Visiting Professor Henan Normal University, Xinxiang, China
- Febr/March 2002: Visiting Scholar, National Institute of Science, Technology and Development Studies,NewDelhi, India
- 2001: Visiting Professor at the Dalian University of Technology, Dalian, China
- Oct-Dec. 2001: John Metcalfe Visitor´s Grant, University of New South Wales, Sydney, Australia
- July-August 2001: Guest Professor, Dalian University of Technology, China
- 1998-2001: Researcher and Lecturer Department of Psychology, Free University Berlin, Germany
- February/March 1998: Visiting Scholar, National Institute of Science, Technology and Development Studies, New Delhi, India
- 1997: CWTS, University of Leiden, The Netherlands
- 1994-1996: Researcher and Lecturer Department of Psychology, Free University Berlin
- 1991-1993: Research Group Leader, Bibliometrics, KAI eV. Berlin
- 1976-1991: Senior Scientist, Institute for Theory, History and Organization of Science, Academy of Sciences of the GDR, Berlin
- 1970-1975: Social Psychologist, Steel Factory, Hennigsdorf
- 2000-present: Co-ordinator and Founder of the Global Interdisciplinary Research
Network COLLNET: "Collaboration in Science and in Technology",Web site: www.collnet.de
- 2007-present: Editor of the „COLLNET Journal of Scientometrics and Information Management“
- 2007-present: Editorial Board Member of the, „Journal of Informetrics“
- 1999-present: Editorial Board member of the international journal "Scientometrics"
- 2004-2006: Associate Editor of the "Journal of Information Management and Scientometrics (Incorporating the COLLNET Journal)"
- 2003-present: Associate Editor of the Chinese journal "Evaluation & Management"
- 1993-present: Member of the International Program Commitee, International Conferences of Scientometrics and Informetrics (I.S.S.I)
- 1993-2003 Board Member, International Society for Scientometrics and Informetrics I.S.S.I.
- 1993-1995: President and Founding Member, International Society for Scientometrics and Informetrics I.S.S.I.