Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
nhung cong » thong cong, hang cong, nhung don
hanh hang » thanh hang, hang hang, hanh han
dung cong » dung trong
doc hieu » toc thieu, hoc thieu, hoc hien
toan cau » toan cao, toan tap, toan tai
toan ban » van ban

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 - hanh hang va ((nhung cong) OR (dung cong)) dan ((toan cau) or (toan ban))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu quang - hanh hang va ((nhung cong) OR (dung cong)) dan ((toan cau) OR (toan ban))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc hieu quang - hanh hang va ((nhung cong) OR (dung cong)) dan ((toan cau) or (toan ban))*".