Perhaps you should try some spelling variations:
dung qsan » dung quan, dung san, dung quang
hieu suat » hieu luat, hieu qua
quang san » quang ban, quang uan, quang van
kien soat » kiem soat, bien soan, kien hoa
qsan van » quan van, quang van, luan van
van hieu » cao hieu
van kien » van tien, van hien, van chien
san van » tan van, luan van, tran van

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( trinh dung qsan van hieu suat ) or ( tinh quang san van kien soat ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( trinh dung qsan van hieu suat ) OR ( tinh quang san van kien soat )).
• Adding a wildcard symbol may retrieve word variants: (( trinh dung qsan van hieu suat ) or ( tinh quang san van kien soat ))*.