Perhaps you should try some spelling variations:
del literatura » de literatura, pela literatura, da literatura
am filosofia » a filosofia, em filosofia, la filosofia
test modell » tekst modell, test model, text modell
test models » trust models, cost models, testing models
studien am » studien a, studien aus, studien auf

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 modell) OR (test models)) studien am filosofia del literatura".
• Adding a wildcard symbol may retrieve word variants: ((test modell) OR (test models)) studien am filosofia del literatura*.