Perhaps you should try some spelling variations:
sach thien » sach thieu, sach tien, cach thien
toc sach » hoc sach, doc 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
thuc va » thuc vat, thuc dan, thuc day
va tinh » may tinh
tinh va » tich va, trinh van, trinh vat
cuu tre » cua tre, cau tren, cau treo
tu tren » tu truyen, tu tieng, tu trong

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

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