Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
doc sach » hoc sach, toc sach, nuoc sach
thuc day » thuc dan, thuc vat
nam thuc » nam thuoc, am thuc, nam thu
dan dai » dat dai, can dai, dan dat
day dan » day danh, dao dan, cay dan
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
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: ((doc sach) or (thuoc sach)) ky ((nang xa) OR (nang ma)) hoi. hieu va nam thuc day dan dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((doc sach) OR (thuoc sach)) ky ((nang xa) OR (nang ma)) hoi. hieu va nam thuc day dan dai cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((doc sach) or (thuoc sach)) ky ((nang xa) OR (nang ma)) hoi. hieu va nam thuc day dan dai cua tre*".