Perhaps you should try some spelling variations:
modell studien » model studies, models studies, moderne studien
de litteratura » de litterature, e letteratura, da literatura
de literatura » de litterature, la literatura, y literatura
test modell » tekst modell, test models, test model

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: test modell studien _ filosofia ((de litteratura) OR (de literatura)).
• Adding a wildcard symbol may retrieve word variants: test modell studien _ filosofia ((de litteratura) or (de literatura))*.