Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
hieu van » hieu va, thien van, lieu va
duc ban » duc tan, duc van, dua ban
cau duc » cao duc, cau luc, chu duc
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
van cau » van dau, van hau, van chat
o hoc » co hoc, mo hoc, so hoc
o hoi » co hoi, o hai, 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 hoc)). hieu van cau duc ban thanh ((dat su) OR (sat su)) triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoi) OR (o hoc)). hieu van cau duc ban thanh ((dat su) OR (sat su)) triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((o hoi) or (o hoc)). hieu van cau duc ban thanh ((dat su) OR (sat su)) triet".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoi) or (o hoc)). hieu van cau duc ban thanh ((dat su) OR (sat su)) triet*.