Perhaps you should try some spelling variations:
nang cai » nang tai, nang cap, nang can
hanh vai » hanh vi, hanh va, hanh tai
hieu van » thien van, lieu va, hieu ve
so sach » so sanh, bo sach, co sach
cam luc » cam xuc, cau luc
vai cua » dai cua, hai cua, lai cua
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
luc va » duc va, tuc va, loc va

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