The volumes of the last five years can be found in the reading rooms at the end of the respective classification. For example, you will find journals of computing (TI) at TIZ and journals of mathematics (MA) at MAZ.
Volumes older than five years are moved to the closed stack. They have to be ordered via catalog and picked up half an hour later.
Journal volumes are for reading room use only.
E-journals may also be looked up at the Elektronische Zeitschriftenbibliothek (EZB).