Perhaps you should try some spelling variations:
20 instability » 2 instability, 10 instability, 26 instability
2c instabilit » sc instability, 2.2 instability, 2.4 instability
2 lehrbucher » 1 lehrbucher, a lehrbucher, _ lehrbuchern
2c lehrbuch » 2 lehrbuch, 1 lehrbuch, es lehrbuch
im lehrbuch » ein lehrbuch, zum lehrbuch, ihk 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))%c3%a4t %((((2c lehrbuch) OR (im lehrbuch))) OR (2 lehrbucher))%22.
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((2c instabilit) or (20 instability))%c3%a4t %((((2c lehrbuch) or (im lehrbuch))) or (2 lehrbucher))%22*.