Perhaps you should try some spelling variations:
des referates » des referats, den referaten, eines referates
wang liang » wang yang
liang des » gang des, liang dan, liang wei
von david » john david, jan david
ben david » bevan david
wan wang » wen wang, yan wang, wang yang
ng tan » wing tan
hong » long

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: wan wang liang des referates ((von david) OR (ben david)) ((ng tan) OR (hong tan)) ;~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "wan wang liang des referates ((von david) or (ben david)) ((ng tan) OR (hong tan)) ;~".
• Adding a wildcard symbol may retrieve word variants: wan wang liang des referates ((von david) or (ben david)) ((ng tan) OR (hong tan)) ;*.