Perhaps you should try some spelling variations:
del literatura » de literatura, pela literatura, da literatura
doe filosofia » de filosofia, e filosofia, di filosofia
studies doe » studies does, studies dose, studies do
tests drug » testing drug, tests during
test drug » best drugs, test du, fast drug

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: "((test drug) OR (tests drug)) studies doe filosofia del literatura".
• Adding a wildcard symbol may retrieve word variants: ((test drug) OR (tests drug)) studies doe filosofia del literatura*.