Perhaps you should try some spelling variations:
toan thanh » tran thanh, hoan thanh, toan thang
thanh dieu » thanh lieu, than dieu, hanh dieu
hieu van » hieu va, thien van, hieu ve
duc toan » duc tan, duc ton, duc hoan
dieu cua » dieu tra
tu sach » thu sach, su sach, te sach
ty nang » ky nang, ty hang, ly nang
cac duc » cac du, cao duc, cac dac
cua te » cua tu
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: tu sach ((ty nang) OR (ty xang)) o hoi. ((hieu van) or (lieu va)) cac duc toan thanh dieu cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ty nang) OR (ty xang)) o hoi. ((hieu van) OR (lieu va)) cac duc toan thanh dieu cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ty nang) OR (ty xang)) o hoi. ((hieu van) or (lieu va)) cac duc toan thanh dieu cua te".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ty nang) OR (ty xang)) o hoi. ((hieu van) or (lieu va)) cac duc toan thanh dieu cua te*.