Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
hoc sach » hoc sinh, hoc cac, hoc anh
nam thuc » nam thuoc, am thuc, nam thu
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang
va dan » ca dan, va dao, va dap
va dau » va dao
va cua » va chua, via cua, ca cua
va nam » van nam, ha nam, va nay

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 lang xa hoi. hieu va nam thuc ((va dan) OR (va dau)) va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ky lang xa hoi. hieu va nam thuc ((va dan) OR (va dau)) va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (hoc sach)) ky lang xa hoi. hieu va nam thuc ((va dan) OR (va dau)) va cua tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sach)) ky lang xa hoi. hieu va nam thuc ((va dan) OR (va dau)) va cua tre*.