Perhaps you should try some spelling variations:
cach thuc » anh thuc, cac thu
cac thuc » cac thu, can thuc, cay thuc
danh vai » danh sai, danh va, doanh van
hieu van » hieu va, thien van, lieu va
so sach » so sanh, bo sach, co sach
vai cua » dai cua, hai cua, lai 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 vai 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 vai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y ((nang xa) or (nang ma)) hoi. hieu van ((cac thuc) OR (cach thuc)) va danh vai 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 vai cua tre*.