Perhaps you should try some spelling variations:
nang cai » nang tai, nang cap, nang can
so sach » so sanh, bo sach, hoc sach
co sach » bo sach, cuon sach, hoc sach
hieu va » lieu va, hieu qua
cac luc » cau luc, coc luc, cac nuoc
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
luc va » duc va, tuc va, loc va
vi cua » vai cua, di 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) OR (co sach)) y ((nang cai) or (nang cao)) hoi. hieu va cac luc va hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((so sach) OR (co sach)) y ((nang cai) OR (nang cao)) hoi. hieu va cac luc va hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((so sach) OR (co sach)) y ((nang cai) or (nang cao)) hoi. hieu va cac luc va hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((so sach) OR (co sach)) y ((nang cai) or (nang cao)) hoi. hieu va cac luc va hanh vi cua tre*.