Perhaps you should try some spelling variations:
grundkurs mathematik » vorkurs mathematik, grundkurs informatik
reviewed studies » related studies, resolved studies, repeated studies
review studies » review study

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: (((( vieweg studium; grundkurs mathematik ) OR ( vieweg studium; bruckenkurs mathematik ))) OR ((( viewed studium; grundkurs mathematik ) OR ( ((reviewed studies) OR (review studies)); grundkurs mathematik )))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(((( vieweg studium; grundkurs mathematik ) or ( vieweg studium; bruckenkurs mathematik ))) or ((( viewed studium; grundkurs mathematik ) or ( ((reviewed studies) OR (review studies)); grundkurs mathematik ))))".
• Adding a wildcard symbol may retrieve word variants: (((( vieweg studium; grundkurs mathematik ) or ( vieweg studium; bruckenkurs mathematik ))) or ((( viewed studium; grundkurs mathematik ) or ( ((reviewed studies) OR (review studies)); grundkurs mathematik ))))*.