Perhaps you should try some spelling variations:
cach thuc » anh thuc, cac thu
cac thuc » cac thu, can thuc, cay thuc
danh hai » dang hai, lanh hai, manh hai
hieu van » hieu va, thien van, lieu va
so sach » so sanh, bo sach, co sach
hai cua » thai cua, dai cua, hoi cua
va danh » va dinh, va dan, va hanh
nang xa » nang x, lang xa, mang xa
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: so sach y ((nang xa) or (nang ma)) hoi. hieu van ((cac thuc) or (cach thuc)) va danh hai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y ((nang xa) OR (nang ma)) hoi. hieu van ((cac thuc) OR (cach thuc)) va danh hai cua tre.
• Adding a wildcard symbol may retrieve word variants: so sach y ((nang xa) or (nang ma)) hoi. hieu van ((cac thuc) or (cach thuc)) va danh hai cua tre*.