Perhaps you should try some spelling variations:
2.4 instability » 3.4 instability, 2.6 instability, 5.2.4 instability
2.2 instability » 7.2 instability, 6.2 instability, 2.6 instability
10 instability » 1 instability, 17 instability, _ instability
26 instability » 2.6 instability, 6 instability, 16 instability
20 instability » 27 instability, 2.6 instability, _ instability
2c instabilit » sc instability, 2.6 instability, c instabilitat
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 %((((2c instabilit) OR (((2.4 instability) OR (2.2 instability))))) OR (((((20 instability) OR (10 instability))) OR (26 instability))))%c3%a4t %zu lehrbuch%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((((2c instabilit) or (((2.4 instability) OR (2.2 instability))))) or (((((20 instability) or (10 instability))) or (26 instability))))%c3%a4t %zu lehrbuch%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((2c instabilit) or (((2.4 instability) OR (2.2 instability))))) or (((((20 instability) or (10 instability))) or (26 instability))))%c3%a4t %zu lehrbuch%22*.