Perhaps you should try some spelling variations:
cua triet » cua viet, su triet, va triet
tang mai » tang ma, tang tai, lang mai
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, dua tren
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
mai hoi » mai khoi, dai hoi, lai hoi
ky tang » ky nang, ky dang, kho tang
tro va » tao va, tho va, tro ba
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky tang mai hoi. ((hieu ve) or (hieu qua)) cac tro va dan vi ((cua tre) OR (cua triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky tang mai hoi. ((hieu ve) OR (hieu qua)) cac tro va dan vi ((cua tre) OR (cua triet))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky tang mai hoi. ((hieu ve) or (hieu qua)) cac tro va dan vi ((cua tre) OR (cua triet))*".