Perhaps you should try some spelling variations:
mittelbar » unmittelbar, ermittelbar, unmittelbare
mittelbare » unmittelbare, ermittelbare, unmittelbaree, unmittelbaren
erunmittelbare » erununmittelbare, erunermittelbare, erununmittelbaree, erununmittelbaren, unmittelbare, ermittelbare, unmittelbar

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