Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, hieu ve
nam thuc » nam thuoc, am thuc, nam thu
thuc dan » thuc hanh, hoc dan, thuc vat
dan hanh » dang hanh, dan khanh, dan thanh
hanh dai » hanh tai, hanh dao, vanh dai
tu sach » thu sach, su sach, te sach
ky dang » ky nang, ky danh
dang xa » dang xay, lang xa, dang ha
cua tre » cua te, cuu tre, cua triet

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu sach) or (toc sach)) ky dang xa hoi. ((hieu van) or (lieu va)) nam thuc dan hanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky dang xa hoi. ((hieu van) OR (lieu va)) nam thuc dan hanh dai cua tre.
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky dang xa hoi. ((hieu van) or (lieu va)) nam thuc dan hanh dai cua tre*.