Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
chieu sang » chieu sach, chieu xanh, hieu lang
hanh tranh » canh tranh, hanh trinh, hanh trang
tranh cua » doanh cua, manh cua
thanh cap » thanh lap, hanh cap, than cap
cong ban » cong bang, cong tan, cong dan
cong san » cong tac

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 quang) OR (chieu sang)) - hanh tranh cua ban ((cong ban) OR (cong san)) thanh cap~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc ((hieu quang) or (chieu sang)) - hanh tranh cua ban ((cong ban) OR (cong san)) thanh cap~".
• Adding a wildcard symbol may retrieve word variants: hoc ((hieu quang) or (chieu sang)) - hanh tranh cua ban ((cong ban) OR (cong san)) thanh cap*.