Perhaps you should try some spelling variations:
mittelbau » mittelbare, mittelbach
ermittelbar » unmittelbar, ermittelbare, erunmittelbar, erunmittelbare
mittelbis » mittelbaus
mittelbar » mittelbare, unmittelbar, unmittelbare

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