Perhaps you should try some spelling variations:
pela literatura » pena literatura, a literatura, de literatura
der filosofia » de filosofia, di filosofia, da filosofia
la literatura » la litterature, a literature
drug studie » drug studies, drugs studies, drugs studied
e filosofia » la filosofia
tests drug » test drug, testing drug, tests during

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