Perhaps you should try some spelling variations:
nam danh » nam dan
tu sach » thu sach, su sach, te sach
cac thu » cach thuc, cac thoi
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
mai hoi » mai khoi, dai hoi, lai hoi
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
ma hoi » xa hoi, ma hoa, me hoi

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