Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, nhung don
hieu lang » chieu sang, hieu quang, nhieu tang
hanh sinh » hanh tinh, hanh dinh, hinh sinh
hang cong » dang cong, hang nong, bang cong
doc hieu » toc thieu, hoc thieu, hoc hien
sinh cua » manh cua, dinh cuu, sinh va
phan cau » phan cac, phan tu, phan lap
phan dau » phan tu, hang dau

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