Perhaps you should try some spelling variations:
sc instability » disc instability, 7 instability, 5 instability
10 instability » 1 instability, 17 instability, _ instability
2c instabilit » 20 instability, 2.2 instability, 2.4 instability
2c lehrbuch » 2 lehrbuch, zu lehrbuch, im lehrbuch
1 lehrbuch » ein lehrbuch, zum lehrbuch, und 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 (10 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 (sc instability))) or (10 instability))%c3%a4t %((2c lehrbuch) OR (1 lehrbuch))%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((2c instabilit) or (sc instability))) or (10 instability))%c3%a4t %((2c lehrbuch) OR (1 lehrbuch))%22*.