Perhaps you should try some spelling variations:
en literatura » e literatura, pena literatura, en litterature
filosofia en » filosofia e, filosofia del, filosofia con
studium des » studium der
tests drug » test drug, testing drug, tests during
studie des » studie der, studie die

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "tests drug ((studie des) OR (studium des)) filosofia en literatura".
• Adding a wildcard symbol may retrieve word variants: tests drug ((studie des) OR (studium des)) filosofia en literatura*.