Perhaps you should try some spelling variations:
dang hanh » dang thanh, ban hanh, dang van
cam thuc » am thuc, nam thuc, cam thu
dan hanh » dan khanh, dan thanh, ban hanh
hieu van » hieu va, thien van, lieu va
cua tre » cua te, cuu tre, cua triet
van cam » van nam, van lam, van cau
nang xa » nang x, lang xa, nang ma
sac ky » cac ky

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

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