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