Perhaps you should try some spelling variations:
dan thuc » dan toc, am thuc
sinh dai » sinh thai, si dai, sinh vat
dinh dai » dinh dat, dinh dao, dinh tai
hieu van » hieu va, thien van, lieu va
thuc va » thuc vat, thuc dan, thuc day
van dan » van ban, ban dan, van dao
sach ky » sach y, sach ty, sach kem
nang xa » nang x, lang xa, nang ma
cua tre » cua te, cuu tre, cua triet
sac ky » cac ky, sai ky

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

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