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

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