Perhaps you should try some spelling variations:
10 instability » _ instability, 7 instability, 5 instability
17 instability » 7 instability, _ instability, 5 instability
2c instabilit » 20 instability, sc instability, 2.2 instability
1 instability » _ instability, 7 instability, 5 instability
2c lehrbuch » 2 lehrbuch, im lehrbuch, es lehrbuch
1 lehrbuch » ein lehrbuch, das 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 (((((10 instability) OR (1 instability))) OR (17 instability))))%c3%a4t %((2c lehrbuch) OR (1 lehrbuch))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((2c instabilit) or (((((10 instability) OR (1 instability))) or (17 instability))))%c3%a4t %((2c lehrbuch) or (1 lehrbuch))%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((2c instabilit) or (((((10 instability) OR (1 instability))) or (17 instability))))%c3%a4t %((2c lehrbuch) or (1 lehrbuch))%22*.