Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
cua tre » cua te, cuu tre, cua triet
tu can » tu cac, thu canh
tu ban » thu ban, te ban
dan vi » doan vi, don vi, dan va
vi cua » vai cua, di cua

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 ky nang ((x ho) or (xa hoi)). hieu vien bach ((tu can) OR (tu ban)) dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((x ho) OR (xa hoi)). hieu vien bach ((tu can) OR (tu ban)) dan vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((x ho) or (xa hoi)). hieu vien bach ((tu can) OR (tu ban)) dan vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((x ho) or (xa hoi)). hieu vien bach ((tu can) OR (tu ban)) dan vi cua tre*.