Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam thu
lang xa » lang ha, dang xay, lang van
tang xa » trang xa, tang ma, tang ha
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
thuc ca » thuc cua, thuc can, thuc cao
vai cau » va cau, van cau, lai chau
vai cac » va cac, tai cac, voi cac
ca dan » cac dan, ca dao
va nam » van nam, ha nam, va nay

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ky ((tang xa) or (lang xa)) hoi. hieu va nam thuc ca dan ((vai cau) OR (vai cac)) treo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ky ((tang xa) OR (lang xa)) hoi. hieu va nam thuc ca dan ((vai cau) OR (vai cac)) treo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ky ((tang xa) or (lang xa)) hoi. hieu va nam thuc ca dan ((vai cau) OR (vai cac)) treo".
• Adding a wildcard symbol may retrieve word variants: doc sach ky ((tang xa) or (lang xa)) hoi. hieu va nam thuc ca dan ((vai cau) OR (vai cac)) treo*.