Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
hanh di » hanh de, hang di, danh di
sach ty » sach y, sach tu, sach thu
van hac » van hoc, van ha, van hai
ty nang » ky nang, ty xang, ty hang
cua tre » cua te, cuu tre, cua triet
hac du » cac du, han du, hac de
du van » duy van, duc van, tu van
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: thu sach ty nang ((x hoi) OR (xa hoi)). hieu van hac du van ((hanh di) or (hanh vi)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ty nang ((x hoi) OR (xa hoi)). hieu van hac du van ((hanh di) OR (hanh vi)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ty nang ((x hoi) OR (xa hoi)). hieu van hac du van ((hanh di) or (hanh vi)) cua tre".
• Adding a wildcard symbol may retrieve word variants: thu sach ty nang ((x hoi) OR (xa hoi)). hieu van hac du van ((hanh di) or (hanh vi)) cua tre*.