Perhaps you should try some spelling variations:
10 instability » 17 instability, 7 instability, 4 instability
2c instabilit » 20 instability, sc instability, 2.2 instability
5 instability » 7 instability
1 instability » 7 instability, 4 instability, 2 instability
im lehrbuch » ein lehrbuch, zum lehrbuch, ihk 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 %((((2c instabilit) OR (5 instability))) OR (((((10 instability) OR (_ instability))) OR (1 instability))))%c3%a4t %im lehrbuch%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((((2c instabilit) or (5 instability))) or (((((10 instability) OR (_ instability))) or (1 instability))))%c3%a4t %im lehrbuch%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((2c instabilit) or (5 instability))) or (((((10 instability) OR (_ instability))) or (1 instability))))%c3%a4t %im lehrbuch%22*.