Perhaps you should try some spelling variations:
en litterature » et litterature, une litterature, la litterature
duales studium » das studium
di filosofia » la filosofia
e filosofia » la filosofia

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: (texto OR textos) duales studium ((di filosofia) OR (e filosofia)) en litterature.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(texto or textos) duales studium ((di filosofia) OR (e filosofia)) en litterature".
• Adding a wildcard symbol may retrieve word variants: (texto or textos) duales studium ((di filosofia) OR (e filosofia)) en litterature*.