Classification
ZBAE - Conferences
5
ZBJD - Libraries and library science - international
4
AFG - Large scale research institutions (Helmholtz Centres)
2
AHC - Research and development, research politics - Germany
2
AXD - Local studies
2
UHK - Traffic and environment - incl. automobile exhaust gas
2
A
1
UMN - Air pollution control and measurement
1
ZBA - Librarianship ( general )
1
ZBHC - Electronic publishing
1