Perhaps you should try some spelling variations:
yang yang » wang yang, wang yan
dong cao » dong xiao, dan cao, dong nan
a patent » a patient, _ patent, a parent
long du » long d, long run, long did
long do » long d, longer do, long ago
a auf » i auf, b auf
ya a » a a, y a, ye a
a au » a bau, a aus, a a

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: ((dong cao) OR (yang yang)) ya a patent ((a au) OR (a auf)) ((long du) OR (long do)) ;~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((dong cao) or (yang yang)) ya a patent ((a au) or (a auf)) ((long du) OR (long do)) ;~".
• Adding a wildcard symbol may retrieve word variants: ((dong cao) or (yang yang)) ya a patent ((a au) or (a auf)) ((long du) OR (long do)) ;*.