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
hoa hoi » khoa hoi, hoa hoc, hoa doi
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
ky lang » ky nang, ky dang, ky tang
ha hoi » ha noi, xa hoi, va hoi
va dan » ca dan, va dao, va dap
va dau » va dao
va cau » van cau, va cac, va cao
va nam » van nam, ha nam, va nay

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) OR (hoa hoi)). hieu va nam thuc ((va dan) or (va dau)) va cau theo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky lang ((ha hoi) OR (hoa hoi)). hieu va nam thuc ((va dan) OR (va dau)) va cau theo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky lang ((ha hoi) OR (hoa hoi)). hieu va nam thuc ((va dan) or (va dau)) va cau theo".
• Adding a wildcard symbol may retrieve word variants: toc sach ky lang ((ha hoi) OR (hoa hoi)). hieu va nam thuc ((va dan) or (va dau)) va cau theo*.