Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
sach ky » sac ky, sach y, sach kem
sach ty » sach y, sach tu, sach thu
van cac » van hac, van cau, van bac
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
cac tu » cac thu, cach tu, cac du
vi cua » vai cua, di cua
x hoi » xa hoi, o hoi, 5 hoi

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: su ((sach ky) OR (sach ty)) nang ((x hoi) OR (x ho)). hieu van cac tu va hanh vi cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sach ty)) nang ((x hoi) OR (x ho)). hieu van cac tu va hanh vi cua tre~".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sach ty)) nang ((x hoi) OR (x ho)). hieu van cac tu va hanh vi cua tre*.