Perhaps you should try some spelling variations:
mittelbau » mittelbare, mittelbach
mittelbar » mittelbare, ermittelbar
unmittelbare » unmittelbaree, unermittelbare, ermittelbar
unmittelbar » unmittelbare, unermittelbar

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: ((mittelbau OR (mittelbar OR unmittelbare)) OR unmittelbar)*.