Perhaps you should try some spelling variations:
canh trinh » canh tranh, hanh trinh, canh tinh
trinh chat » tinh chat, trinh luat, trinh han
chat quang » chat luong, pham quang
cong thanh » dong thanh, cong trinh, truong thanh
hieu sang » chieu sang, hieu quang, nhieu tang
hieu lang » chieu sang, hieu quang, nhieu tang
cong tan » cong tac, cong san, cong ty
toan ban » van ban

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 sang) or (hieu lang)) - canh trinh chat quang ((cong thanh) OR (cong tan)) toan ban~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc ((hieu sang) OR (hieu lang)) - canh trinh chat quang ((cong thanh) OR (cong tan)) toan ban.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc ((hieu sang) or (hieu lang)) - canh trinh chat quang ((cong thanh) OR (cong tan)) toan ban".
• Adding a wildcard symbol may retrieve word variants: doc ((hieu sang) or (hieu lang)) - canh trinh chat quang ((cong thanh) OR (cong tan)) toan ban*.