Perhaps you should try some spelling variations:
dang xay » dang van, van xay
hieu van » hieu va, thien van, lieu va
van thai » van thoai, van tai, van hai
thai son » thai den, thai do, thai hoc
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
va hanh » van hanh, va thanh, va danh
tai cua » thai cua, tri cua, dai cua
son va » song va, son la, lon va

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: so sach ky ((nang x) OR (dang xay)) hoi. hieu van thai son va hanh ((tai cua) OR (tai cuc)) tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ky ((nang x) or (dang xay)) hoi. hieu van thai son va hanh ((tai cua) OR (tai cuc)) tre~".
• Adding a wildcard symbol may retrieve word variants: so sach ky ((nang x) or (dang xay)) hoi. hieu van thai son va hanh ((tai cua) OR (tai cuc)) tre*.