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

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 nang o hoc. hieu van am thuc va ((hanh dai) OR (vanh dai)) su viet~.
• 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) OR (vanh dai)) su viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) ky nang o hoc. hieu van am thuc va ((hanh dai) OR (vanh dai)) su viet".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ky nang o hoc. hieu van am thuc va ((hanh dai) OR (vanh dai)) su viet*.