Perhaps you should try some spelling variations:
mittelbar » mittelbare, unmittelbar
ermittelbar » ermittelbare, erunmittelbar, unmittelbar
unmittelbare » unmittelbaree, ununmittelbare, unmittelbar
mittelbisau » mittelbau, mittelbis

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: ((mittelbar OR (ermittelbar OR unmittelbare)) OR mittelbisau).
• Adding a wildcard symbol may retrieve word variants: ((mittelbar or (ermittelbar or unmittelbare)) or mittelbisau)*.