Perhaps you should try some spelling variations:
sc instability » disc instability, 5 instability, 4 instability
20 instability » 10 instability, 26 instability, 27 instability
7 instability » _ instability
2 instability » _ instability, 5 instability, 4 instability
zu lehrbuch » zum lehrbuch, 1 lehrbuch, 2 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 (7 instability))) OR (((20 instability) OR (2 instability))))%c3%a4t %zu lehrbuch%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((((sc instability) OR (7 instability))) or (((20 instability) or (2 instability))))%c3%a4t %zu lehrbuch%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((sc instability) OR (7 instability))) or (((20 instability) or (2 instability))))%c3%a4t %zu lehrbuch%22*.