Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
canh trinh » canh tranh, hanh trinh, canh tinh
luat chung » luan chung, luat thuong, cua chung
luan cong » luat cong, luong cong, luan chung
doc hieu » toc thieu, hoc thieu, hoc hien
cong tan » cong tac, cong san, cong thanh
tan van » tran van, tang van, luan van

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc hieu quang - canh trinh ((luan cong) or (luat chung)) cong tan van ban~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu quang - canh trinh ((luan cong) OR (luat chung)) cong tan van ban.
• Adding a wildcard symbol may retrieve word variants: doc hieu quang - canh trinh ((luan cong) or (luat chung)) cong tan van ban*.