Perhaps you should try some spelling variations:
del literature » model literature, abel literature, fuel literature
des filosofia » de filosofia, e filosofia, di filosofia
safe studien » aue studien, safety studies, duale studien
safe studio » slate studio, game studio, life studio

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: tests ((safe studien) OR (safe studio)) des filosofia del literature.
• Adding a wildcard symbol may retrieve word variants: tests ((safe studien) or (safe studio)) des filosofia del literature*.