Perhaps you should try some spelling variations:
credit trading » credit training, credit rating, credit standing
trading value » trading volume, trading volumes, creating value
dual credit » rural credit, equal credit, rural credits
value cong » value co
yang yang » wang yang, wang yan, wang yong
a dual » _ dual

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (((dong or done) sin) or (yang yang)) a dual credit trading value cong shu ;~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((dong OR done) sin) OR (yang yang)) a dual credit trading value cong shu ;*.