Perhaps you should try some spelling variations:
le literature » e literature, 2e literature, ce literature
tests stable » tests table, sets stable, test table
filosofia le » filosofia de, filosofia e, filosofia del
studien es » studien aus, studien bei, studien ein
studien e » studien _, studien 3, studien 4

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: tests stable ((studien e) OR (studien es)) filosofia le literature.
• Adding a wildcard symbol may retrieve word variants: tests stable ((studien e) or (studien es)) filosofia le literature*.