Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
nhung cong » dung cong, thong cong, hang cong
cong thanh » dong thanh, cong trinh, cong tan
doc hieu » toc thieu, hoc thieu, hoc hien
trung va » truong va, trang va, trung tam
trung ha » trung hoc, trung tam, trung cap
hoa ban » hoa dan, hoa han, hoa tan
hoa van » hoa dan, hoang van, hoa phan

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 quang - thanh ((trung va) OR (trung ha)) nhung cong thanh ((hoa ban) OR (hoa van))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc hieu quang - thanh ((trung va) or (trung ha)) nhung cong thanh ((hoa ban) OR (hoa van))~".
• Adding a wildcard symbol may retrieve word variants: doc hieu quang - thanh ((trung va) or (trung ha)) nhung cong thanh ((hoa ban) OR (hoa van))*.