Perhaps you should try some spelling variations:
dan thanh » dang thanh, danh thanh, van thanh
ban thanh » ban hanh, ban hang
tang mai » tang ma, tang tai, lang mai
hieu van » hieu va, thien van, lieu va
cam thuc » am thuc, nam thuc, cam thu
so sach » so sanh, bo sach, co sach
mai hoi » mai khoi, dai hoi, lai hoi
van cam » van nam, van lam, van cau
y tang » ky tang, 6 tang, 7 tang
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 y tang mai 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 y tang mai hoi. hieu van cam thuc ((dan thanh) OR (ban thanh)) dai cua tu.
• Adding a wildcard symbol may retrieve word variants: so sach y tang mai hoi. hieu van cam thuc ((dan thanh) or (ban thanh)) dai cua tu*.