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
ihk lehrbuch » ein lehrbuch, und lehrbuch, das lehrbuch
2c lehrbuch » 1 lehrbuch, zu lehrbuch, es lehrbuch
im lehrbuch » ein lehrbuch, zum lehrbuch, dem lehrbuch
2 lehrbuch » 1 lehrbuch, 2 lehrbucher, zu lehrbuch

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "%22str%c3%b6mungsmechanik %((2c instabilit) OR (20 instability))%c3%a4t %((((2c lehrbuch) OR (((im lehrbuch) OR (ihk lehrbuch))))) OR (2 lehrbuch))%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 (ihk lehrbuch))))) OR (2 lehrbuch))%22*.