Perhaps you should try some spelling variations:
2.6 instability » 2.2 instability, 2.6 stability, 2 instability
2.4 instability » 3.4 instability, 2.2 instability, 5.2.4 instability
16 instability » 1 instability, 10 instability, 17 instability
20 instability » 2 instability, 10 instability, 27 instability
26 instability » 2 instability, 27 instability, 2.2 instability
6 instability » _ instability, 7 instability, 5 instability
2c instabilit » sc instability, 2 instability, 2.2 instability
2c lehrbuch » 2 lehrbuch, 1 lehrbuch, im 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 (((20 instability) OR (((((((26 instability) OR (((2.6 instability) OR (2.4 instability))))) OR (16 instability))) OR (6 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 (((20 instability) or (((((((26 instability) or (((2.6 instability) OR (2.4 instability))))) or (16 instability))) or (6 instability))))))%c3%a4t %2c lehrbuch%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((2c instabilit) or (((20 instability) or (((((((26 instability) or (((2.6 instability) OR (2.4 instability))))) or (16 instability))) or (6 instability))))))%c3%a4t %2c lehrbuch%22*.