Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, nhung don
hanh huong » thanh huong, anh huong, manh huong
hieu lang » chieu sang, hieu quang, nhieu tang
huong cua » dung cua
hang cong » dang cong, hang nong, bang cong
doi hieu » doi chieu, doc hieu, doi hien
dan toan » dan than, manh toan, xuan toan
van toan » van tuan, van tan, van thanh

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: doi hieu lang - hanh huong cua ((nhung cong) OR (hang cong)) ((dan toan) OR (van toan)) cao~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doi hieu lang - hanh huong cua ((nhung cong) or (hang cong)) ((dan toan) OR (van toan)) cao~".
• Adding a wildcard symbol may retrieve word variants: doi hieu lang - hanh huong cua ((nhung cong) or (hang cong)) ((dan toan) OR (van toan)) cao*.