Perhaps you should try some spelling variations:
hermann ebooks » german books
a robert » 3 robert, dr robert, a robot
robert e » robert _, robert j
a robust » _ robust
robust e » robust _, robust a, robust end
book » ebook
books » ebooks
ebooks » eebooks

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: (( a robert e. heitmann (book OR books) ) OR ( a robust e. hermann ebooks ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( a robert e. heitmann (book OR books) ) or ( a robust e. hermann ebooks ))~".
• Adding a wildcard symbol may retrieve word variants: (( a robert e. heitmann (book OR books) ) or ( a robust e. hermann ebooks ))*.