Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
tu sach » thu sach, te sach, tu cach
su sach » so sach, vu sach
qua cac » cua cac
cac duc » cac du, cao duc, cac dac
va hang » van hang, va nang, va lang
hang vi » hang va, hanh vi, hang di
cua tre » cua te, cuu tre, cua triet
vi cua » vai cua, di cua
x hoi » xa hoi, o hoi, x ho

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 (su sach))) or (toc sach)) ky nang x hoi. hieu qua cac duc va hang vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((((tu sach) OR (su sach))) OR (toc sach)) ky nang x hoi. hieu qua cac duc va hang vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((tu sach) OR (su sach))) or (toc sach)) ky nang x hoi. hieu qua cac duc va hang vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((((tu sach) OR (su sach))) or (toc sach)) ky nang x hoi. hieu qua cac duc va hang vi cua tre*.