Perhaps you should try some spelling variations:
tinh huong » dinh huong, tinh quang, anh huong
dung lang » dung dang, dung nang, dung land
hieu soat » hieu suat, hieu hoat, hieu luat
tinh dung » tin dung, tinh quang, anh dung
kien hoat » kien hoa, dien hoat, trien hoat
lang van » dang van, tang van, hoang van
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: (( trinh dung lang van hieu soat ) OR ( ((tinh dung) OR (tinh huong)) quan van kien hoat ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( trinh dung lang van hieu soat ) or ( ((tinh dung) OR (tinh huong)) quan van kien hoat ))~".
• Adding a wildcard symbol may retrieve word variants: (( trinh dung lang van hieu soat ) or ( ((tinh dung) OR (tinh huong)) quan van kien hoat ))*.