Perhaps you should try some spelling variations:
sc instability » disc instability, 7 instability, 5 instability
20 instability » 2 instability, 10 instability, 26 instability
4 instability » _ instability, 7 instability, 5 instability
zum lehrbuch » ein lehrbuch
zu lehrbuch » 1 lehrbuch, 2 lehrbuch, ein lehrbuch

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: %22str%c3%b6mungsmechanik %((sc instability) OR (((20 instability) OR (4 instability))))%c3%a4t %((zu lehrbuch) OR (zum lehrbuch))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((sc instability) or (((20 instability) or (4 instability))))%c3%a4t %((zu lehrbuch) OR (zum lehrbuch))%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((sc instability) or (((20 instability) or (4 instability))))%c3%a4t %((zu lehrbuch) OR (zum lehrbuch))%22*.