Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dien cua » dieu cua, dien cuc, dien cu
va thanh » gia thanh, ban thanh, va tinh
ban hanh » ban hang
hieu van » hieu va, thien van, lieu va
cau duc » cao duc, cau luc, chu duc
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
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: toc sach ky nang o hoi. ((hieu ve) OR (hieu van)) cau duc ((ban hanh) or (va thanh)) dien cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky nang o hoi. ((hieu ve) OR (hieu van)) cau duc ((ban hanh) OR (va thanh)) dien cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky nang o hoi. ((hieu ve) OR (hieu van)) cau duc ((ban hanh) or (va thanh)) dien cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky nang o hoi. ((hieu ve) OR (hieu van)) cau duc ((ban hanh) or (va thanh)) dien cua tre*.