Perhaps you should try some spelling variations:
luong quan » thong quan, duong qua
hieu suat » hieu luat, hieu qua
hieu soat » hieu hoat, hieu luat, kiem soat
tin luong » tien luong, tin huong, tin tuong
dung tan » dung toan, duong tan, dung tai
quan vat » quan va, quan sat, quan van
vat bien » vat lieu, cam bien
tan van » tran van, tang van, luan van
bien so » bien doi

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 tan van ((hieu soat) OR (hieu suat)) ) OR ( tin luong quan vat bien so ))~.
• Adding a wildcard symbol may retrieve word variants: (( trinh dung tan van ((hieu soat) or (hieu suat)) ) or ( tin luong quan vat bien so ))*.