Perhaps you should try some spelling variations:
filosofia de » filosofia del
l filosofia » la filosofia, e filosofia, a filosofia
studien l » studien _, studien 3, studien 4
test den » test der, test des, testen den
test de » test der, test des, est de

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 den) OR (test de)) studien l filosofia de (literatur* OR literature*).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((test den) OR (test de)) studien l filosofia de (literatur* or literature*)".
• Adding a wildcard symbol may retrieve word variants: ((test den) OR (test de)) studien l filosofia de (literatur* or literature*)*.