Perhaps you should try some spelling variations:
tang mai » tang ma, tang tai, lang mai
cam thuc » am thuc, nam thuc, cam thu
hieu van » hieu va, thien van, lieu va
mai hoi » mai khoi, dai hoi, lai hoi
hieu ve » hieu va
thuc va » thuc vat, thuc dan, thuc day
dan vi » doan vi, don vi, dan va
va dan » ca dan, va dao, va dau
vi hoa » voi hoa, vi hoc, va hoa
sai ky » sac ky

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

• Performing a fuzzy search may retrieve terms with similar spellings: so ((cac ky) or (sai ky)) tang mai hoi. ((hieu ve) OR (hieu van)) cam thuc va dan vi hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so ((cac ky) OR (sai ky)) tang mai hoi. ((hieu ve) OR (hieu van)) cam thuc va dan vi hoa viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so ((cac ky) or (sai ky)) tang mai hoi. ((hieu ve) OR (hieu van)) cam thuc va dan vi hoa viet".
• Adding a wildcard symbol may retrieve word variants: so ((cac ky) or (sai ky)) tang mai hoi. ((hieu ve) OR (hieu van)) cam thuc va dan vi hoa viet*.