Perhaps you should try some spelling variations:
thanh dai » thanh hai, thanh tai, thanh dat
dan thanh » dang thanh, danh thanh, ban thanh
dang xay » dang van, van xay
thuc dan » thuc hanh, hoc dan, thuc vat
cam thuc » am thuc, nam thuc, cam thu
hieu van » hieu va, thien van, lieu va
van cam » van nam, van lam, van cau
so sach » bo sach, co sach, hoc sach
lang xa » lang ha, lang van
so sanh » do sanh
cua su » qua su

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((so sach) or (so sanh)) tay ((lang xa) OR (dang xay)) hoi. hieu van cam thuc dan thanh dai cua su~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((so sach) OR (so sanh)) tay ((lang xa) OR (dang xay)) hoi. hieu van cam thuc dan thanh dai cua su.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((so sach) or (so sanh)) tay ((lang xa) OR (dang xay)) hoi. hieu van cam thuc dan thanh dai cua su".
• Adding a wildcard symbol may retrieve word variants: ((so sach) or (so sanh)) tay ((lang xa) OR (dang xay)) hoi. hieu van cam thuc dan thanh dai cua su*.