Perhaps you should try some spelling variations:
lam thuc » lam thuoc, am thuc, nam thuc
tinh voi » trinh voi, tinh doi, binh voi
hieu van » hieu va, thien van, lieu va
thuc va » thuc vat, thuc dan, thuc day
tinh vi » trinh vi, tinh va, dinh vi
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
van lam » van nam
nang ma » tang ma, sang ma, nang cao
cua tre » cua te, cuu tre, cua triet

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

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