Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dau tren » dau tien, dat tren, dau tieng
nam thuc » nam thuoc, am thuc, nam thu
sach thu » sach thue, sach thieu, sach tham
thuc va » thuc vat, thuc dan, thuc day
hieu va » lieu va, hieu qua
cu tren » tu tren, dua tren
lang ha » long ha
lang xa » dang xay, lang van
va dan » ca dan, va dao, va dau
dan va » doan va, dan ca, ban va
va nam » van nam, ha nam, va nay

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 thu ((lang xa) or (lang ha)) hoi. hieu va nam thuc va dan va ((dau tren) or (cu tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach thu ((lang xa) OR (lang ha)) hoi. hieu va nam thuc va dan va ((dau tren) OR (cu tren)).
• Adding a wildcard symbol may retrieve word variants: toc sach thu ((lang xa) or (lang ha)) hoi. hieu va nam thuc va dan va ((dau tren) or (cu tren))*.