Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
dang xay » dang van
nam thuc » nam thuoc, am thuc, nam thu
doc sach » hoc sach, nuoc sach, dac sac
hieu va » lieu va, hieu qua
thuc va » thuc vat, thuc dan, thuc day
dan vat » dang vat, van vat, dan va
vat cua » mat cua, bat cua, dat cua
cua tre » cua te, cuu tre, cua triet
va nam » van nam, ha nam, va nay
va dan » ca dan, va dao, va dau

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