Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
hanh va » hang va, hanh vi
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
hieu va » lieu va, hieu qua
cua chu » sua chua
sach ty » sach tu, sach thu, xach tay
va cua » va chua, via cua, ca cua
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: su ((sach ty) OR (sach y)) xang ((xa hoi) or (o hoi)). hieu va cac duc van hanh va cua chu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ty) OR (sach y)) xang ((xa hoi) OR (o hoi)). hieu va cac duc van hanh va cua chu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ty) OR (sach y)) xang ((xa hoi) or (o hoi)). hieu va cac duc van hanh va cua chu".
• Adding a wildcard symbol may retrieve word variants: su ((sach ty) OR (sach y)) xang ((xa hoi) or (o hoi)). hieu va cac duc van hanh va cua chu*.