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