Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cap nuoc » dat nuoc
kho tang » cao tang
doan vi » doan va, don vi, doan thi
hieu va » lieu va, hieu qua
ky tang » ky nang, ky dang, ky trong
lai hoi » dai hoi, lai hoa, lai roi
va cap » va cac, va dap, va cao
dan vi » don vi, dan va, gan vi

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 ((ky tang) OR (kho tang)) lai hoi. hieu va cap nuoc va ((dan vi) or (doan vi)) cau thi~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky tang) OR (kho tang)) lai hoi. hieu va cap nuoc va ((dan vi) OR (doan vi)) cau thi.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky tang) OR (kho tang)) lai hoi. hieu va cap nuoc va ((dan vi) or (doan vi)) cau thi".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky tang) OR (kho tang)) lai hoi. hieu va cap nuoc va ((dan vi) or (doan vi)) cau thi*.