Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
dang xay » dang van, van xay
xay hoi » xa hoi, tay hoi, cay phoi
hieu va » hieu qua
thuc va » thuc vat, thuc dan, thuc day
y dang » ky dang, 2 dang, _ dang
va dan » ca dan, va dao, va dau
va chu » va che, va chi
va cau » van cau, va cac, va dau

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: toc sach y dang xay hoi. ((hieu va) OR (lieu va)) nam thuc va dan ((va chu) OR (va cau)) tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y dang xay hoi. ((hieu va) or (lieu va)) nam thuc va dan ((va chu) OR (va cau)) tre~".
• Adding a wildcard symbol may retrieve word variants: toc sach y dang xay hoi. ((hieu va) or (lieu va)) nam thuc va dan ((va chu) OR (va cau)) tre*.