Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
trinh vi » trinh va, trinh ve, trinh viet
su sach » so sach, vu sach
tinh vi » tinh voi, tinh va, dinh vi
nam xuc » cam xuc, nam xua, nam thuc
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
xuc va » duc va, tuc va, luc va
o hoi » co hoi, o hoc, o hai

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 ((o hoi) or (xa hoi)). hieu van nam xuc va ((tinh vi) OR (trinh vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang ((o hoi) OR (xa hoi)). hieu van nam xuc va ((tinh vi) OR (trinh vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang ((o hoi) or (xa hoi)). hieu van nam xuc va ((tinh vi) OR (trinh vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang ((o hoi) or (xa hoi)). hieu van nam xuc va ((tinh vi) OR (trinh vi)) cua tre*.