Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
va triet » va thiet, va trien, ve triet
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
cao duc » dao duc, cao suc, giao duc
va hanh » van hanh, va thanh, va danh
ve cao » va cao, ve bao, ve cac
cua te » cua tu
x hoi » xa hoi, x ho, 5 hoi
o hoi » co hoi, o hoc, o hai

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ky nang ((x hoi) OR (o hoi)). hieu ve cao duc va hanh vi ((cua te) or (va triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky nang ((x hoi) OR (o hoi)). hieu ve cao duc va hanh vi ((cua te) OR (va triet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky nang ((x hoi) OR (o hoi)). hieu ve cao duc va hanh vi ((cua te) or (va triet))".
• Adding a wildcard symbol may retrieve word variants: doc sach ky nang ((x hoi) OR (o hoi)). hieu ve cao duc va hanh vi ((cua te) or (va triet))*.