Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
cau theo » cau thi, cau tao
lang ha » long ha
ky lang » ky nang, ky dang, ky tang
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
vat cau » dat cau, va cau, van cau
ha hoi » hoa hoi, ha noi, xa hoi
va nam » van nam, ha nam, va nay
va dan » ca dan, va dao, va dap
va dau » va 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 ha hoi. hieu va nam thuc ((va dan) OR (va dau)) vat cau theo~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky lang ha hoi. hieu va nam thuc ((va dan) OR (va dau)) vat cau theo".
• Adding a wildcard symbol may retrieve word variants: toc sach ky lang ha hoi. hieu va nam thuc ((va dan) OR (va dau)) vat cau theo*.