Perhaps you should try some spelling variations:
nhanh mang » nhanh lang, hanh mang, nhanh quang
nhung cong » thong cong, hang cong, nhung don
hieu lang » chieu sang, hieu quang, nhieu tang
dung cong » dung trong
hoc hieu » hoc thieu, hoc hien, doc hieu
anh tang » anh bang, anh dang, anh nang
san van » tan van, luan van, tran van

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: hoc hieu lang - ((anh tang) OR (nhanh mang)) cua ((nhung cong) OR (dung cong)) san van ban~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc hieu lang - ((anh tang) or (nhanh mang)) cua ((nhung cong) OR (dung cong)) san van ban~".
• Adding a wildcard symbol may retrieve word variants: hoc hieu lang - ((anh tang) or (nhanh mang)) cua ((nhung cong) OR (dung cong)) san van ban*.