Perhaps you should try some spelling variations:
disc instability » disk instability, disks instability, disc stability
2.2 instability » 7.2 instability, 6.2 instability, 2.4 instability
sc instability » 7 instability, 5 instability, 1 instability
10 instability » 1 instability, 17 instability, _ instability
2c instabilit » 20 instability, 2.4 instability, 2.6 instability
4 instability » _ instability, 7 instability, 5 instability
2c lehrbuch » 2 lehrbuch, 1 lehrbuch, zu 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 (2.2 instability))) OR (((sc instability) OR (disc instability))))) OR (((10 instability) OR (4 instability))))%c3%a4t %2c lehrbuch%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((((((2c instabilit) or (2.2 instability))) or (((sc instability) OR (disc instability))))) or (((10 instability) or (4 instability))))%c3%a4t %2c lehrbuch%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((((2c instabilit) or (2.2 instability))) or (((sc instability) OR (disc instability))))) or (((10 instability) or (4 instability))))%c3%a4t %2c lehrbuch%22*.