Perhaps you should try some spelling variations:
hieu vien » hieu viec, thieu nien, hieu tieng
hieu hien » bieu hien, dieu hien, chieu chien
su sach » so sach, vu sach
cac dat » cac dan, cai dat, cac dai
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
vi cua » vai cua, di cua
x hoi » o hoi, x ho, 5 hoi

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: su sach y nang ((x hoi) OR (xa hoi)). ((hieu vien) or (hieu hien)) cac dat va hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang ((x hoi) OR (xa hoi)). ((hieu vien) OR (hieu hien)) cac dat va hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y nang ((x hoi) OR (xa hoi)). ((hieu vien) or (hieu hien)) cac dat va hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach y nang ((x hoi) OR (xa hoi)). ((hieu vien) or (hieu hien)) cac dat va hanh vi cua tre*.