Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, nam thu, nam tu
sach ky » sac ky, sach y, sach ty
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
hieu va » lieu va, hieu qua
dao va » dao van, tao va, cao va
do va » do van, so va

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