Perhaps you should try some spelling variations:
da literatura » la literatura, a literatura, de literatura
de filosofia » di filosofia, la filosofia, a filosofia
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.

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