Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
vien bac » vien bach, vien cac, mien bac
sach ky » sac ky, sach ty, sach kem
dan dai » dat dai, can dai, dan dat
cua tre » cua te, cuu tre, cua triet
bac tu » ban tu, tac tu, cac tu
ca dan » cac dan, ca dao
tu ca » tu cac, tu cua, tu can

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