Perhaps you should try some spelling variations:
thanh do » thanh de, thanh pho, thanh hoa
dang xay » dang van, van xay
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
nang xa » nang x, lang xa, nang ma
cua tre » cua te, cuu tre, cua triet
tac va » tac xa, tuc va, tac ha
do cua » doi cua, co cua, de 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 ky ((nang xa) or (dang xay)) hoi. hieu va cac ((tac va) OR (tac da)) thanh do cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky ((nang xa) OR (dang xay)) hoi. hieu va cac ((tac va) OR (tac da)) thanh do cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky ((nang xa) or (dang xay)) hoi. hieu va cac ((tac va) OR (tac da)) thanh do cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky ((nang xa) or (dang xay)) hoi. hieu va cac ((tac va) OR (tac da)) thanh do cua tre*.