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