Perhaps you should try some spelling variations:
del literatura » de literatura, pela literatura, da literatura
tests duale » tests due, tests scale, tests damage
studien die » studie die, studien der
studien de » studien der, studien des, studien dd

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 duale ((studien de) OR (studien die)) filosofia del literatura".
• Adding a wildcard symbol may retrieve word variants: tests duale ((studien de) OR (studien die)) filosofia del literatura*.