Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
thuc day » thuc dan, thuc vat
ky lang » ky dang, ky tang, tay lang
hieu va » lieu va
day dan » day danh, dao dan, cay dan
dan vai » dan va, dan tai, dan vat
vai cuu » vai cua
cuu tre » cua tre, cau tren, cau treo

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) or (ky nang)) xa hoi. ((hieu va) OR (hieu qua)) nam thuc day dan vai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky nang)) xa hoi. ((hieu va) OR (hieu qua)) nam thuc day dan vai cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) or (ky nang)) xa hoi. ((hieu va) OR (hieu qua)) nam thuc day dan vai cuu tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) or (ky nang)) xa hoi. ((hieu va) OR (hieu qua)) nam thuc day dan vai cuu tre*.