Perhaps you should try some spelling variations:
level literature » legal literature, levels literatur, travel literature
novel literature » model literature, travel literature, cordel literature
duales studium » das studium
test duales » test doubles, test rules, test oracles

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 duales studium _ filosofia ((level literature) OR (novel literature))".
• Adding a wildcard symbol may retrieve word variants: test duales studium _ filosofia ((level literature) OR (novel literature))*.