Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dang xay » dang van, van xay
thuc day » thuc dan, thuc vat
sach ty » sach y, sach tu, sach thu
thuc va » thuc vat, thuc dan
hieu va » lieu va, hieu qua
xay hoi » xa hoi, tay hoi, cay phoi
ty dang » ty xang, ky dang, ty hang
va nam » van nam, ha nam, va nay
va cuu » va cau, va chu
va huu » vu huu

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