Perhaps you should try some spelling variations:
2.2 instability » 7.2 instability, 6.2 instability, 2.4 instability
17 instability » 7 instability, 1 instability, 10 instability
20 instability » 10 instability, 27 instability, 2.4 instability
26 instability » 2.6 instability, 27 instability, 2.4 instability
16 instability » 1 instability, 10 instability, 12 instability
6 instability » _ instability, 7 instability, 5 instability
2c instabilit » sc instability, 2.4 instability, 2.6 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 (2.2 instability))) OR (((20 instability) OR (((((26 instability) OR (((16 instability) OR (17 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 (2.2 instability))) or (((20 instability) or (((((26 instability) or (((16 instability) OR (17 instability))))) or (6 instability))))))%c3%a4t %2c lehrbuch%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((2c instabilit) or (2.2 instability))) or (((20 instability) or (((((26 instability) or (((16 instability) OR (17 instability))))) or (6 instability))))))%c3%a4t %2c lehrbuch%22*.