Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
ky tang » ky nang, ky dang, kho tang
ky lang » ky nang, ky dang, tay lang
hieu va » lieu va, hieu qua
vai cuu » vai cua
cuu tre » cua tre, cau tren, cau treo
va nam » van nam, ha nam, va nay
va dao » ca dao

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ((ky lang) OR (ky tang)) xa hoi. hieu va nam thuc ((va dao) or (va dau)) vai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky tang)) xa hoi. hieu va nam thuc ((va dao) OR (va dau)) vai cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) OR (ky tang)) xa hoi. hieu va nam thuc ((va dao) or (va dau)) vai cuu tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) OR (ky tang)) xa hoi. hieu va nam thuc ((va dao) or (va dau)) vai cuu tre*.