Perhaps you should try some spelling variations:
quang quan » quang tuan, quang uan, quan quan
hieu suat » hieu luat, hieu qua
kien soat » kiem soat, bien soan, kien hoa
dung lan » dung land, dung lam, dung san
van hieu » cao hieu
quan van » luan van, quan va, quan luan
van kien » van tien, van hien, van chien

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 lan) OR (dung luan)) van hieu suat ) OR ( tinh quang quan van kien soat ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( tinh ((dung lan) OR (dung luan)) van hieu suat ) or ( tinh quang quan van kien soat ))~".
• Adding a wildcard symbol may retrieve word variants: (( tinh ((dung lan) OR (dung luan)) van hieu suat ) or ( tinh quang quan van kien soat ))*.