Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu van
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
va dan » va dao, va dau, va dap
ca dan » cac dan, ca dao
vi cua » vai cua, di cua

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. ((hieu ve) or (hieu va)) cac tro ((va dan) OR (ca dan)) vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky tang ma hoi. ((hieu ve) OR (hieu va)) cac tro ((va dan) OR (ca dan)) vi cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky tang ma hoi. ((hieu ve) or (hieu va)) cac tro ((va dan) OR (ca dan)) vi cua tre*".