Perhaps you should try some spelling variations:
stifter studien » seiner studien, stadler studien
filosofia della » filosofia del, filosofia de
tests stifter » tests after, tests filter, tests sites
filosofia e » filosofia de, filosofia del
studien de » studien der, studien die, studien des

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 stifter studien de ((filosofia della) OR (filosofia e)) literatura.
• Adding a wildcard symbol may retrieve word variants: tests stifter studien de ((filosofia della) or (filosofia e)) literatura*.