Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
dung cong » dung trong
ban tang » ban trang, ban hang, ba tang
tang vat » tang van, dang vat, bang vat
vat dung » van dung, va dung, viet dung
toan cao » toan ban
toan tap » toan ban
ho hieu » ho chieu, hoi hieu, nho hieu

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: ho hieu quang - ban tang vat dung cong trinh ((toan cao) OR (toan tap))~.
• Adding a wildcard symbol may retrieve word variants: ho hieu quang - ban tang vat dung cong trinh ((toan cao) or (toan tap))*.