Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam thu
cau tren » cu tren, dau tren, ca tren
hieu va » lieu va, hieu qua
thuc va » thuc vat, thuc dan, thuc day
dan vai » dan va, dan tai, dan vat
cuu tre » cua tre, cau treo
ha hoi » hoa hoi, xa hoi, va hoi
va nam » van nam, ha nam, va nay
y lang » o lang, _ lang, tay lang
va dan » ca dan, va dao, 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: doc sach y lang ((ha hoi) OR (ha noi)). hieu va nam thuc va dan vai ((cuu tre) OR (cau tren))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach y lang ((ha hoi) OR (ha noi)). hieu va nam thuc va dan vai ((cuu tre) or (cau tren))~".
• Adding a wildcard symbol may retrieve word variants: doc sach y lang ((ha hoi) OR (ha noi)). hieu va nam thuc va dan vai ((cuu tre) or (cau tren))*.