Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
dam thuc » am thuc, dan thuc, nam thuc
doc sach » hoc sach, nuoc sach, dac sac
hanh lam » thanh lap, hanh kem, hanh va
vat hanh » vat thanh, van hanh, va hanh
cua tre » cua te, cuu tre, cua triet
su viet » so viet
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
y nang » ky nang, ly nang, v nang
va dam » van dam, va dao, va dau

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 (doc sach)) y nang ma hoa. hieu va dam thuc vat hanh lam ((cua tre) or (su viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) y nang ma hoa. hieu va dam thuc vat hanh lam ((cua tre) OR (su viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) y nang ma hoa. hieu va dam thuc vat hanh lam ((cua tre) or (su viet))".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) y nang ma hoa. hieu va dam thuc vat hanh lam ((cua tre) or (su viet))*.