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