Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
hanh dai » hanh tai, hanh dao, vanh dai
vu sach » vu bach, su sach, vu khach
nang xa » nang x, lang xa, nang ma
hieu va » lieu va
dau duc » dao duc, dang duc, dau nuoc
duc van » duc va, duc tan, duc manh
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu sach y ((nang xa) or (nang cao)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach y ((nang xa) OR (nang cao)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu sach y ((nang xa) or (nang cao)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: vu sach y ((nang xa) or (nang cao)) hoi. ((hieu va) OR (hieu qua)) dau duc van hanh dai cua tre*.