Perhaps you should try some spelling variations:
20 instability » 2 instability, 10 instability, 26 instability
sc instability » disc instability, 5 instability, 4 instability
7 instability » _ instability
1 instability » _ instability, 5 instability, 4 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 %((((20 instability) OR (sc instability))) OR (((7 instability) OR (1 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 %((((20 instability) or (sc instability))) or (((7 instability) or (1 instability))))%c3%a4t %((2c lehrbuch) OR (1 lehrbuch))%22".
• Adding a wildcard symbol may retrieve word variants: %22str%c3%b6mungsmechanik %((((20 instability) or (sc instability))) or (((7 instability) or (1 instability))))%c3%a4t %((2c lehrbuch) OR (1 lehrbuch))%22*.