Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
ty nang » ky nang, ty xang, ty hang
sach ty » sach y, sach tu, sach thu
hoc dua » hoc cua, hoc duc, hoc lua
minh ve » dinh ve, minh va, kinh ve
cua tre » cua te, cuu tre, cua triet
hoc du » hoc duc, hoc dau, hoc su
ve cua » le cua, de cua, te cua
x hoi » xa hoi, x ho, 5 hoi
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: thu sach ty nang ((x hoi) or (o hoi)). hieu van ((hoc du) OR (hoc dua)) van minh ve cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ty nang ((x hoi) OR (o hoi)). hieu van ((hoc du) OR (hoc dua)) van minh ve cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ty nang ((x hoi) or (o hoi)). hieu van ((hoc du) OR (hoc dua)) van minh ve cua tre".
• Adding a wildcard symbol may retrieve word variants: thu sach ty nang ((x hoi) or (o hoi)). hieu van ((hoc du) OR (hoc dua)) van minh ve cua tre*.