Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
hieu van » hieu va, thien van, lieu va
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
sach tu » sach thu, cach tu, sach ty
thuc va » thuc vat, thuc dan, thuc day
so viet » hoc viet
va dan » ca dan, va dao, va dau
dan ki » dan ky, dan ke, dan li

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: thu sach tu ((nang xa) OR (nang ma)) hoi. hieu van nam thuc va dan ki ((su viet) OR (so viet))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach tu ((nang xa) or (nang ma)) hoi. hieu van nam thuc va dan ki ((su viet) OR (so viet))~".
• Adding a wildcard symbol may retrieve word variants: thu sach tu ((nang xa) or (nang ma)) hoi. hieu van nam thuc va dan ki ((su viet) OR (so viet))*.