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

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