Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
van cac » van hac, van cau, van bac
sach ky » sac ky, sach y, sach kem
sach ty » sach y, sach tu, sach thu
cua tre » cua te, cuu tre, cua triet
tuc va » thuc va, truc va, duc va
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.

• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach ty)) nang x hoi. hieu van cac ((tuc va) OR (tuc xa)) 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. hieu van cac ((tuc va) OR (tuc xa)) hanh vi cua tre~".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sach ty)) nang x hoi. hieu van cac ((tuc va) OR (tuc xa)) hanh vi cua tre*.