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