Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam thu
vai cua » dai cua, hai cua, lai cua
cua tre » cua te, cuu tre, cua triet
hieu va » lieu va, hieu qua
ky dang » ky nang, ky danh
ky lang » ky nang, ky tang, tay lang
ha hoi » hoa hoi, ha noi, xa hoi
va dan » ca dan, va dao, va dap
va dau » va dao
va nam » van nam, ha nam, va nay

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: doc sach ((ky lang) OR (ky dang)) ha hoi. hieu va nam thuc ((va dan) OR (va dau)) vai cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ((ky lang) or (ky dang)) ha hoi. hieu va nam thuc ((va dan) OR (va dau)) vai cua tre~".
• Adding a wildcard symbol may retrieve word variants: doc sach ((ky lang) or (ky dang)) ha hoi. hieu va nam thuc ((va dan) OR (va dau)) vai cua tre*.