Perhaps you should try some spelling variations:
cac tren » ca tren, cau tren, rac tren
hieu van » hieu va, thien van, lieu va
nang ha » nang hai, nang han, nang hoa
thuc va » thuc vat, thuc dan, thuc day
dinh va » dinh van, tinh va, sinh va
dinh ve » dinh ket, dinh van
ha hoi » hoa hoi, ha noi, xa hoi
sac ky » cac ky
van am » van nam, van lam, van dam

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

• If you are trying to use Boolean operators, they must be ALL CAPS: te ((sac ky) OR (sai ky)) nang ha hoi. hieu van am thuc va ((dinh va) OR (dinh ve)) cac tren~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sac ky) or (sai ky)) nang ha hoi. hieu van am thuc va ((dinh va) OR (dinh ve)) cac tren~".
• Adding a wildcard symbol may retrieve word variants: te ((sac ky) or (sai ky)) nang ha hoi. hieu van am thuc va ((dinh va) OR (dinh ve)) cac tren*.