In the departmental libraries frequently used textbooks and other basic course material is grouped together and shelved separately in the textbook collection.
Typical for the textbook collection is that each book title is held in several loanable copies, mostly for 30 days. The copies can be recognized by a red dot sticker on the spine and a call number label containing 080 (e.g. QA 080).
If all copies are on loan you can check the library catalogue for further copies that may be shelved in other departmental libraries.