Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cau theo » cau thi, cau tao
sach ky » sac ky, sach y, sach ty
thuc va » thuc vat, thuc dan, thuc day
dan vai » dan va, dan tai, dan vat
vai cau » va cau, van cau, vai cac
va nam » van nam, va nay
va dan » ca dan, va dao, va dau
x hoi » xa hoi, o hoi, 5 hoi

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