Perhaps you should try some spelling variations:
thanh do » thanh de, thanh pho, thanh hoa
thanh di » thanh doi, thanh de, thanh dinh
hieu van » hieu va, thien van, lieu va
tu sach » thu sach, su sach, te sach
cac luc » cau luc, coc luc, cac nuoc
luc gia » luoc gia, duc gia, quoc gia
van cac » van hac, van cau, van bac
sach ty » sach y, sach tu, sach thu
ty nang » ky nang, ty xang, ty hang
cua tre » cua te, cuu tre, cua triet
x hoi » o hoi, x ho, 5 hoi

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 ((x hoi) or (xa hoi)). hieu van cac luc gia ((thanh di) OR (thanh do)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty nang ((x hoi) OR (xa hoi)). hieu van cac luc gia ((thanh di) OR (thanh do)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty nang ((x hoi) or (xa hoi)). hieu van cac luc gia ((thanh di) OR (thanh do)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ty nang ((x hoi) or (xa hoi)). hieu van cac luc gia ((thanh di) OR (thanh do)) cua tre*.