Perhaps you should try some spelling variations:
la literatura » la litterature, a literature
tests stable » tests table, sets stable, test table
filosofia la » filosofia da, filosofia le, filosofica da
tests safe » tests safety, tests scale, tests space
studien la » studien lap, studien a, studien l

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) OR (tests safe)) studien la filosofia la literatura.
• Adding a wildcard symbol may retrieve word variants: ((tests stable) or (tests safe)) studien la filosofia la literatura*.