Perhaps you should try some spelling variations:
thong cong » trong cong, tong cong, thong thong
hieu lang » chieu sang, hieu quang, nhieu tang
cua thong » cua thuong, cua khong, cua tong
doc hieu » toc thieu, hoc thieu, hoc hien
cong tan » cong tac, cong san, cong thanh
toan cau » toan ban, toan tap, toan tai
toan cao » toan ban, toan tap
can van » cac van, can ban, tan van
van cua » vang cua, ban cua, dan cua

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 lang - can van cua thong cong tan ((toan cau) or (toan cao))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu lang - can van cua thong cong tan ((toan cau) OR (toan cao)).
• Adding a wildcard symbol may retrieve word variants: doc hieu lang - can van cua thong cong tan ((toan cau) or (toan cao))*.