Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, nam thu, nam tu
sach ky » sac ky, sach y, sach ty
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
hieu va » hieu qua
dau vai » dau va, dau hai, dau tai
vai cuu » vai cua
cuu tre » cua tre, cau tren, cau treo
va dau » va dao

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 lang xa hoi. ((hieu va) OR (lieu va)) ((nam thuc) OR (am thuc)) va dau vai cuu tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky lang xa hoi. ((hieu va) OR (lieu va)) ((nam thuc) OR (am thuc)) va dau vai cuu tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky lang xa hoi. ((hieu va) OR (lieu va)) ((nam thuc) OR (am thuc)) va dau vai cuu tre*.