Perhaps you should try some spelling variations:
quang tan » quang tuan, quang tran, quang toan
hieu soat » hieu suat, hieu hoat, hieu luat
dung san » dong san, dung sai, dung luan
dung van » duong van, dung va, dang van
van kien » van tien, van hien, van chien
kien hoa » dien hoa, tien hoa, kien ha
tan van » tran van, tang van, luan 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 san) or (dung van)) cao hieu soat ) or ( tinh quang tan van kien hoa ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( trinh ((dung san) OR (dung van)) cao hieu soat ) OR ( tinh quang tan van kien hoa )).
• Adding a wildcard symbol may retrieve word variants: (( trinh ((dung san) or (dung van)) cao hieu soat ) or ( tinh quang tan van kien hoa ))*.