Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
dan dien » doan dien, danh dien, dan den
cau thuc » cau truc, cuu thuc, can thuc
thuc va » thuc vat, thuc dan, thuc day
sach ky » sac ky, sach y, sach ty
van cau » van dau, van hau, van chat
nang ma » tang ma, sang ma, nang cao
nang xa » nang x, lang xa, mang xa
cuu tre » cua tre, cau tren, cau treo
va dan » ca dan, va dao, va dau
cu tre » cu tren, cua tre, cu tri

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 ((nang xa) or (nang ma)) hoi. hieu van cau thuc va dan dien ((cu tre) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky ((nang xa) OR (nang ma)) hoi. hieu van cau thuc va dan dien ((cu tre) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: thu sach ky ((nang xa) or (nang ma)) hoi. hieu van cau thuc va dan dien ((cu tre) or (cuu tre))*.