Perhaps you should try some spelling variations:
hieu quang » thieu quang, hieu quan, hieu qua
hanh tranh » canh tranh, hanh trinh, hanh trang
manh toan » thanh toan, anh tuan, tinh toan
hoc hieu » hoc thieu, hoc hien, doc hieu
cua dung » cua dang, cua dong, cua rung
qua dung » quang dung, su dung, qua song
san toan » van toan, dan toan, xuan toan

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: hoc hieu quang - hanh tranh ((cua dung) or (qua dung)) cong ((san toan) OR (manh toan)) cao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc hieu quang - hanh tranh ((cua dung) OR (qua dung)) cong ((san toan) OR (manh toan)) cao.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc hieu quang - hanh tranh ((cua dung) or (qua dung)) cong ((san toan) OR (manh toan)) cao".
• Adding a wildcard symbol may retrieve word variants: hoc hieu quang - hanh tranh ((cua dung) or (qua dung)) cong ((san toan) OR (manh toan)) cao*.