Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
dan thanh » dang thanh, danh thanh, van thanh
hieu van » hieu va, thien van, lieu va
cam thuc » am thuc, nam thuc, cam thu
van cam » van nam, van lam, van cau
so sach » so sanh, bo sach, co sach
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
sach v » sach va, sach y, sach 2
cua tu » cua tuc, cua su, cua cu

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 v ((nang xa) OR (nang ma)) hoi. hieu van cam thuc ((dan thanh) or (ban thanh)) dai cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach v ((nang xa) OR (nang ma)) hoi. hieu van cam thuc ((dan thanh) OR (ban thanh)) dai cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach v ((nang xa) OR (nang ma)) hoi. hieu van cam thuc ((dan thanh) or (ban thanh)) dai cua tu".
• Adding a wildcard symbol may retrieve word variants: so sach v ((nang xa) OR (nang ma)) hoi. hieu van cam thuc ((dan thanh) or (ban thanh)) dai cua tu*.