Perhaps you should try some spelling variations:
hieu hien » bieu hien, dieu hien, chieu chien
hieu vien » hieu viec, thieu nien, hieu tieng
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
bach tu » bach thu, cach tu, bac tu
dan dai » dat dai, can dai, dan dat
cua tre » cua te, cuu tre, cua triet
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 nang ((x ho) or (xa hoi)). ((hieu vien) OR (hieu hien)) bach tu ca dan dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang ((x ho) OR (xa hoi)). ((hieu vien) OR (hieu hien)) bach tu ca dan dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang ((x ho) or (xa hoi)). ((hieu vien) OR (hieu hien)) bach tu ca dan dai cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang ((x ho) or (xa hoi)). ((hieu vien) OR (hieu hien)) bach tu ca dan dai cua tre*.