Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
va dinh » van dinh, va kinh, va tinh
hieu va » lieu va, hieu qua
va chao » va cao, va chat, va cham
nang o » nang co, nang ho, nang ro
vi dua » vi du, vi lua
vi dum » vi du
o hoi » co hoi, o hoc, o hai
xu va » xu van, tu va, su va

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

• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ky nang o hoi. hieu va chao xu va dinh ((vi dua) OR (vi dum)) tren~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) ky nang o hoi. hieu va chao xu va dinh ((vi dua) OR (vi dum)) tren~".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ky nang o hoi. hieu va chao xu va dinh ((vi dua) OR (vi dum)) tren*.