Perhaps you should try some spelling variations:
cac thuc » cach thuc, cac thu, can thuc
vai cua » dai cua, hai cua, lai cua
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
nang ma » tang ma, sang ma, nang cao
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
va dao » ca dao
ma hoi » mai hoi, xa hoi, ma hoa

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 nang ma hoi. ((hieu ve) or (hieu qua)) cac thuc ((va dau) OR (va dao)) vai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ma hoi. ((hieu ve) OR (hieu qua)) cac thuc ((va dau) OR (va dao)) vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ma hoi. ((hieu ve) or (hieu qua)) cac thuc ((va dau) OR (va dao)) vai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ma hoi. ((hieu ve) or (hieu qua)) cac thuc ((va dau) OR (va dao)) vai cua tre*.