Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, su sach, te sach
duc van » duc va, duc tan, duc manh
dau duc » dao duc, dang duc, dau nuoc
hieu va » lieu va
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
cua tre » cua te, cuu tre, cua triet
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: tu sach y ((nang xa) or (nang ma)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y ((nang xa) OR (nang ma)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y ((nang xa) or (nang ma)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y ((nang xa) or (nang ma)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh vi cua tre*.