Perhaps you should try some spelling variations:
sc instability » disc instability, 7 instability, 5 instability
20 instability » 2 instability, 10 instability, 26 instability
2c instabilit » 2.2 instability, 2.4 instability, 2.6 instability
im lehrbuch » ein lehrbuch, zum lehrbuch, ihk lehrbuch
1 lehrbuch » ein lehrbuch, das lehrbuch, ihk lehrbuch
2 lehrbuch » 2 lehrbucher, ein lehrbuch, das 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 (sc instability))) OR (20 instability))%c3%a4t %((((1 lehrbuch) OR (im lehrbuch))) OR (2 lehrbuch))%22.
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((2c instabilit) or (sc instability))) or (20 instability))%c3%a4t %((((1 lehrbuch) or (im lehrbuch))) or (2 lehrbuch))%22*.