Perhaps you should try some spelling variations:
10 instability » 1 instability, 17 instability, _ instability
2c instabilit » 20 instability, sc instability, 2.2 instability
2c lehrbuch » 2 lehrbuch, 1 lehrbuch, es lehrbuch
im lehrbuch » ein lehrbuch, zum lehrbuch, ihk lehrbuch
zu lehrbuch » 1 lehrbuch, 2 lehrbuch, ein 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 (10 instability))%c3%a4t %((((2c lehrbuch) OR (im lehrbuch))) OR (zu lehrbuch))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((2c instabilit) or (10 instability))%c3%a4t %((((2c lehrbuch) OR (im lehrbuch))) or (zu lehrbuch))%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((2c instabilit) or (10 instability))%c3%a4t %((((2c lehrbuch) OR (im lehrbuch))) or (zu lehrbuch))%22*.