Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
te sach » toc sach
cac dac » cac dan, cac dai, cac bac
cac duc » cac du, cao duc, cac nuoc
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
mai hoi » mai khoi, dai hoi, lai hoi
sach v » sach va, sach y, sach 2
v nang » va nang, vu nang, van nang
vi cua » vai cua, di cua

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

• If you are trying to use Boolean operators, they must be ALL CAPS: te sach v nang ((ma hoa) OR (mai hoi)). hieu ve ((cac duc) OR (cac dac)) van hanh vi cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sach v nang ((ma hoa) or (mai hoi)). hieu ve ((cac duc) OR (cac dac)) van hanh vi cua tre~".
• Adding a wildcard symbol may retrieve word variants: te sach v nang ((ma hoa) or (mai hoi)). hieu ve ((cac duc) OR (cac dac)) van hanh vi cua tre*.