Perhaps you should try some spelling variations:
dung ltan » dung luan, dung tai, dung nhan
hieu suat » hieu luat, hieu qua
quang tan » quang tuan, quang tran, quang toan
ltan van » luan van, lan van, tran van
van hieu » cao hieu
van bien » van tien, van hien, vat 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.

• Performing a fuzzy search may retrieve terms with similar spellings: (( trinh dung ltan van hieu suat ) or ( tinh quang tan van bien so ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( trinh dung ltan van hieu suat ) OR ( tinh quang tan van bien so )).
• Adding a wildcard symbol may retrieve word variants: (( trinh dung ltan van hieu suat ) or ( tinh quang tan van bien so ))*.