Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
thuc dan » hoc dan, thuc vat
vanh dai » van dai, vanh tai, lanh dao
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
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: ((te sach) or (toc sach)) ky lang xa hoi. hieu van nam ((thuc dan) OR (thuc hanh)) vanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ky lang xa hoi. hieu van nam ((thuc dan) OR (thuc hanh)) vanh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) ky lang xa hoi. hieu van nam ((thuc dan) OR (thuc hanh)) vanh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ky lang xa hoi. hieu van nam ((thuc dan) OR (thuc hanh)) vanh dai cua tre*.