Perhaps you should try some spelling variations:
"schaffen schwache grundlagen" » "schaffen sachliche grundlagen", "schaffen fachliche grundlagen", "schaffen einfache grundlagen", "schaffen schaffen grundlagen", "starken schwache grundlagen"
"schwache schwache grundlagen" » "schwache sachliche grundlagen", "schwache fachliche grundlagen", "schwache einfache grundlagen"

Try widening your search to All Fields.

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: (("schaffen schwache grundlagen") OR ("schwache schwache grundlagen")).
• Removing quotes may allow a broader search: (( schaffen schwache grundlagen ) or ( schwache schwache grundlagen )).
• Adding a wildcard symbol may retrieve word variants: (("schaffen schwache grundlagen") or ("schwache schwache grundlagen"))*.