Perhaps you should try some spelling variations:
nam thuc » nam thuoc, nam thu, nam tu
cao hoi » cau hoi, cao hoc, tao hoi
hieu va » lieu va, hieu qua
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
tu cai » tu cac, tu can, tu bai
cai ky » cao ky, cac ky, cam ky
co hoi » co hoc, co loi
vi cua » vai cua, di cua

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 cai ky nang ((cao hoi) OR (co hoi)). hieu va ((nam thuc) OR (am thuc)) va hanh vi cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu cai ky nang ((cao hoi) OR (co hoi)). hieu va ((nam thuc) or (am thuc)) va hanh vi cua tre~".
• Adding a wildcard symbol may retrieve word variants: tu cai ky nang ((cao hoi) OR (co hoi)). hieu va ((nam thuc) or (am thuc)) va hanh vi cua tre*.