Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
ky dang » ky nang, ky danh
hieu va » lieu va, hieu qua
ky lang » ky nang, ky tang, tay lang
thuc va » thuc vat, thuc dan, thuc day
vai cau » van cau, vai cac, lai chau
ha hoi » hoa hoi, ha noi, xa hoi
va dan » ca dan, va dao, va dau
va cau » van cau, va cac, va dau
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) or (ky dang)) ha hoi. hieu va nam thuc va dan ((vai cau) OR (va cau)) theo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky dang)) ha hoi. hieu va nam thuc va dan ((vai cau) OR (va cau)) theo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) or (ky dang)) ha hoi. hieu va nam thuc va dan ((vai cau) OR (va cau)) theo".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) or (ky dang)) ha hoi. hieu va nam thuc va dan ((vai cau) OR (va cau)) theo*.