Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
sach thu » sach thue, sach thieu, sach tham
hieu van » hieu va, thien van, lieu va
sach ty » sach y, sach tu, xach tay
van cac » van hac, van cau, van bac
cua tre » cua te, cuu tre, cua triet
co hai » co dai, o hai, so hai
cac so » cac co, cac bo, cac ho
so van » su van, vo van
vi cua » vai cua, di cua
co hoi » co hoc, co loi

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

• Performing a fuzzy search may retrieve terms with similar spellings: te ((sach ty) OR (sach thu)) nang ((co hai) or (co hoi)). hieu van cac so van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sach ty) OR (sach thu)) nang ((co hai) OR (co hoi)). hieu van cac so van hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ty) OR (sach thu)) nang ((co hai) or (co hoi)). hieu van cac so van hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: te ((sach ty) OR (sach thu)) nang ((co hai) or (co hoi)). hieu van cac so van hanh vi cua tre*.