Perhaps you should try some spelling variations:
2.2 instability » 7.2 instability, 6.2 instability, 2.4 instability
20 instability » 26 instability, 2.4 instability, 2.6 instability
27 instability » 7 instability, 26 instability, 37 instability
10 instability » 1 instability, _ instability, 7 instability
17 instability » 7 instability, 1 instability, _ 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 %((((2.2 instability) OR (((20 instability) OR (27 instability))))) OR (((10 instability) OR (17 instability))))%c3%a4t %2c lehrbuch%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((((2.2 instability) or (((20 instability) OR (27 instability))))) or (((10 instability) or (17 instability))))%c3%a4t %2c lehrbuch%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((2.2 instability) or (((20 instability) OR (27 instability))))) or (((10 instability) or (17 instability))))%c3%a4t %2c lehrbuch%22*.