Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
tinh via » tinh gia, tinh va, tinh giao
tu sach » thu sach, su sach, te sach
tinh vi » trinh vi, tinh voi, tinh va
cac duc » cac du, cao duc, cac dac
hieu va » lieu va, hieu qua
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
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) or (toc sach)) ky tang ma hoi. hieu va cac duc va ((tinh via) OR (tinh vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky tang ma hoi. hieu va cac duc va ((tinh via) OR (tinh vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (toc sach)) ky tang ma hoi. hieu va cac duc va ((tinh via) OR (tinh vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky tang ma hoi. hieu va cac duc va ((tinh via) OR (tinh vi)) cua tre*.