Perhaps you should try some spelling variations:
thanh hai » thanh phan, thanh hoa, thanh san
thanh dat » thanh san, thanh van, thanh ha
su triet » su viet, su tien, ve triet
hieu van » hieu va, thien van, lieu va
cau duc » cao duc, cau luc, chu duc
tu sach » thu sach, su sach, te sach
van cau » van dau, van hau, van chat
sach ky » sac ky, sach y, sach ty
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 ((thanh dat) OR (thanh hai)) su triet~.
• 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 ((thanh dat) OR (thanh hai)) su triet.
• 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 ((thanh dat) OR (thanh hai)) su triet".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoi) or (o hai)). hieu van cau duc va ((thanh dat) OR (thanh hai)) su triet*.