Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
sach ky » sac ky, sach y, sach ty
vai cua » dai cua, hai cua, lai cua
dan vai » dan va, dan tai, dan vat
hieu va » lieu va, hieu qua
tang ma » mang may, tang van
hieu ve » hieu van
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
tro va » tao va, tho va, tro ha
tro ba » tho ba, tro ha, tro xa

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

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