Perhaps you should try some spelling variations:
hieu quan » hieu qua, lieu quan, thien quan
hang cong » dang cong, hang nong, bang cong
dung cong » dung trong
doc hieu » toc thieu, hoc thieu, hoc hien
tang cua » hang cua, tang luan, thong cua
mang cua » manh cua, dung cua, ban cua
tap doan » tap quan
doan cau » toan cau, doan dau, doan cap

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 quan - hanh ((tang cua) or (mang cua)) ((hang cong) or (dung cong)) tap doan cau~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu quan - hanh ((tang cua) OR (mang cua)) ((hang cong) OR (dung cong)) tap doan cau.
• Adding a wildcard symbol may retrieve word variants: doc hieu quan - hanh ((tang cua) or (mang cua)) ((hang cong) or (dung cong)) tap doan cau*.