Perhaps you should try some spelling variations:
chat thien » phat trien, cai thien, phat hien
chat triet » chet triet, phat trien, cua triet
hieu van » hieu va, thien van, lieu va
cau duc » cao duc, cau luc, chu duc
hanh va » hang va, hanh vi
va hanh » van hanh, va thanh, va danh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
van cau » van dau, van hau, van chat
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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

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