Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
cau tren » cu tren, dau tren, ca tren
dang xay » dang van, van xay
xay hoi » xa hoi, tay hoi, cay phoi
hieu va » hieu qua
sach ky » sac ky, sach y, sach ty
ky dang » ky nang, ky danh
vai cau » va cau, van cau, vai cac
va dan » ca dan, va dau, va dap
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 dang xay hoi. ((hieu va) or (lieu va)) nam thuc ((va dan) or (va dao)) vai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky dang xay hoi. ((hieu va) OR (lieu va)) nam thuc ((va dan) OR (va dao)) vai cau tren.
• Adding a wildcard symbol may retrieve word variants: toc sach ky dang xay hoi. ((hieu va) or (lieu va)) nam thuc ((va dan) or (va dao)) vai cau tren*.