Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu luc » hieu luat, hieu qua
hieu cac » hieu va, hieu van, vien cac
va tinh » may tinh
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
ma hoi » mai hoi, xa hoi, ma hoa
va dan » ca dan, va dao, va dau

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ky tang ma hoi. ((hieu cac) or (hieu luc)) cau truc ((va tinh) or (va dan)) dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky tang ma hoi. ((hieu cac) OR (hieu luc)) cau truc ((va tinh) OR (va dan)) dai cua tre.
• Adding a wildcard symbol may retrieve word variants: thu sach ky tang ma hoi. ((hieu cac) or (hieu luc)) cau truc ((va tinh) or (va dan)) dai cua tre*.