Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
dang xay » dang van, van xay
hieu van » hieu va, thien van, lieu va
van cac » van hac, van cau, van bac
su sach » so sach, vu sach
xang xa » lang xa, mang xa, ang xa
cua tre » cua te, cuu tre, cua triet
xuc va » tuc va, luc va, xac 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: su sach thu ((xang xa) or (dang xay)) hoi. hieu van cac ((xuc va) OR (duc va)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach thu ((xang xa) OR (dang xay)) hoi. hieu van cac ((xuc va) OR (duc va)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach thu ((xang xa) or (dang xay)) hoi. hieu van cac ((xuc va) OR (duc va)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach thu ((xang xa) or (dang xay)) hoi. hieu van cac ((xuc va) OR (duc va)) hanh vi cua tre*.