Perhaps you should try some spelling variations:
dang xay » dang van, van xay
van hanh » van thanh, ban hanh, van anh
hieu va » lieu va, hieu qua
va hanh » va thanh, va danh, ban hanh
tai cua » thai cua, tai cuc, tri cua
cua tre » cua te, cuu tre, cua triet
tu sac » tu sach, tu cac, tu san
sac ky » cac ky, sai ky
va cau » van cau, va cac, va dau

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sac ky ((nang cao) OR (dang xay)) hoi. hieu va cau truc ((va hanh) OR (van hanh)) tai cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sac ky ((nang cao) or (dang xay)) hoi. hieu va cau truc ((va hanh) OR (van hanh)) tai cua tre~".
• Adding a wildcard symbol may retrieve word variants: tu sac ky ((nang cao) or (dang xay)) hoi. hieu va cau truc ((va hanh) OR (van hanh)) tai cua tre*.