Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
van hanh » van thanh, ban hanh, van anh
hanh di » hanh vi, hanh de, hang di
toc van » hoc van, toc san, tac van
cac toc » cac toi, cac nuoc, cac thoi
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va
van hoi » van hoa, van hoc, van hoe
ky tang » ky dang, kho tang, ky trong
di cua » dai cua, doi cua, de cua

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

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