Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh hai » thanh hai, nhanh hai, hang hai
hieu van » hieu va, thien van, lieu va
van cham » van chat, van tham, va cham
cua viet » ca viet, hoa viet, cua vat
cao hoc » co hoc, cho hoc, chat hoc
hai cua » thai cua, dai cua, hoi cua
sach v » sach va, sach y, sach 2
xuc va » duc va, tuc va, xac va
luc va » duc va, tuc va, loc va
v nang » va nang, vu nang, van nang

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach v nang ((cau hoi) or (cao hoc)). hieu van cham ((xuc va) OR (luc va)) hanh hai cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach v nang ((cau hoi) OR (cao hoc)). hieu van cham ((xuc va) OR (luc va)) hanh hai cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach v nang ((cau hoi) or (cao hoc)). hieu van cham ((xuc va) OR (luc va)) hanh hai cua viet".
• Adding a wildcard symbol may retrieve word variants: toc sach v nang ((cau hoi) or (cao hoc)). hieu van cham ((xuc va) OR (luc va)) hanh hai cua viet*.