Perhaps you should try some spelling variations:
sach han » sach tham, sach danh, sach nang
dua tren » dung tren
sach van » sach va, bach van, cach van
cau thuc » cau truc, cuu thuc, can thuc
thuc van » thuc vat, thuc dan, thuc va
van hanh » van thanh, ban hanh, van anh
hanh de » hanh ve, hanh kem
hieu ve » hieu va, hieu van
ve cau » ke cau, va cau, ve cac
nang o » nang co, nang ho, nang ro
cua te » cua tu
o hoc » co hoc, mo hoc, so hoc

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach van) OR (sach han)) nang o hoc. hieu ve cau thuc van hanh de ((dua tren) or (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach van) OR (sach han)) nang o hoc. hieu ve cau thuc van hanh de ((dua tren) OR (cua te))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach van) OR (sach han)) nang o hoc. hieu ve cau thuc van hanh de ((dua tren) or (cua te))*".