Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
lang van » dang van, tang van, hoang van
dang xay » dang van, van xay
vai cua » dai cua, hai cua, lai cua
vat dan » va dan, van dan, vat ran
qua nam » quan nam, cua nam, quang nam
sach ky » sac ky, sach y, sach ty

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

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