Perhaps you should try some spelling variations:
tinh dung » trinh dung, tin dung, tinh huong
dung qtan » dung quan, dung quang, dung tai
hieu soat » hieu suat, hieu hoat, hieu luat
quang tan » quang tuan, quang tran, quang toan
qtan van » tan van, quan van, quang van
van hieu » cao hieu
van bien » van tien, van hien, van kien
vat bien » vat lieu, cam bien

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: (( tinh dung qtan van hieu soat ) OR ( tinh quang tan ((van bien) OR (vat bien)) soan ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( tinh dung qtan van hieu soat ) or ( tinh quang tan ((van bien) OR (vat bien)) soan ))~".
• Adding a wildcard symbol may retrieve word variants: (( tinh dung qtan van hieu soat ) or ( tinh quang tan ((van bien) OR (vat bien)) soan ))*.