Perhaps you should try some spelling variations:
hieu xanh » chieu xanh, hieu manh, hieu nganh
cong tinh » cong trinh, cong vinh, cong thanh
long tinh » trong tinh, luong tin, dong tin
doc hieu » toc thieu, hoc thieu, hoc hien
trung va » truong va, trang va, trung ha
tran van » luan van
toan cao » toan ban, toan tap

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