Perhaps you should try some spelling variations:
mittelbau » mittelbach
mittelbar » unmittelbar, ermittelbar
mittelbare » unmittelbare, ermittelbare, unmittelbaren
unmittelbare » ununmittelbare, unermittelbare, ununmittelbaren, unmittelbar, ermittelbar

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 (mittelbare OR unmittelbare)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((mittelbau or mittelbar) or (mittelbare OR unmittelbare))".
• Adding a wildcard symbol may retrieve word variants: ((mittelbau or mittelbar) or (mittelbare OR unmittelbare))*.