Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
hoc sach » hoc sinh, hoc cac, hoc anh
ky tang » ky nang, ky dang, kho tang
tang ma » mang may, tang van
va hanh » van hanh, va thanh, va danh
ma hoi » mai hoi, xa hoi, ma hoa
va cai » va cac, va bai, va dai
va cao » va cac, va co, va 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: ((toc sach) OR (hoc sach)) ky tang ma hoi. hieu ((va cai) or (va cao)) duc va hanh vi cua vat~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ky tang ma hoi. hieu ((va cai) OR (va cao)) duc va hanh vi cua vat.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (hoc sach)) ky tang ma hoi. hieu ((va cai) or (va cao)) duc va hanh vi cua vat".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (hoc sach)) ky tang ma hoi. hieu ((va cai) or (va cao)) duc va hanh vi cua vat*.