Perhaps you should try some spelling variations:
quang doan » quan doan, quang hoan, quang toan
binh gian » binh giang, binh giai, tinh gian
hieu suat » hieu luat, hieu qua
doan vat » doan va, doan van, dan vat
vat bien » vat lieu, cam bien
gian van » giang van, gian dan, gian lan
ban hieu » van hieu, gian hieu, phan hieu
bien so » bien doi
tinh » trinh, dinh, minh

You may be able to get more results by adjusting your search query.

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