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