Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
sach ky » sac ky, sach y, sach ty
thuc va » thuc vat, thuc dan, thuc day
hieu va » hieu qua
dang xa » dang xay, lang xa, dang ha
ky dang » ky nang, ky danh
va dan » ca dan, va dao, va dau
va cua » va chua, via cua, ma cua
ca cua » co cua

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