Perhaps you should try some spelling variations:
la literature » la litterature, a literature, la literatura
tests stable » tests table, sets stable, test table
filosofia la » filosofia da, filosofia le, filosofica da
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 la literature.
• Adding a wildcard symbol may retrieve word variants: tests stable ((studien e) or (studien es)) filosofia la literature*.