Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
hanh dai » hanh tai, hanh dao, vanh dai
su triet » su viet, su tien, ve triet
thuc va » thuc vat, thuc dan, thuc day
va hanh » van hanh, va thanh, va danh
nang o » nang co, nang ho, nang ro
van am » van nam, van lam, van dam
dai su » dai sua, dai so, dan su
o hoc » co hoc, mo hoc, so hoc

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

• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ky nang o hoc. hieu van am thuc va hanh dai su triet~.
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ky nang o hoc. hieu van am thuc va hanh dai su triet*.