Perhaps you should try some spelling variations:
tham thuc » nham thuc, pham thuc, tam thuc
hanh dai » hanh tai, hanh dao, vanh dai
tai khoi » tai khoa, mai khoi, tao khoi
su sach » so sach, vu sach
tai hoi » dai hoi, tai hai, tai hoe
hieu ve » hieu van
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
hieu va » lieu va, hieu qua
cua te » cua tu
y nang » ky nang, ly nang, v nang

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach y nang ((tai hoi) or (tai khoi)). ((hieu ve) OR (hieu va)) tham thuc va hanh dai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang ((tai hoi) OR (tai khoi)). ((hieu ve) OR (hieu va)) tham thuc va hanh dai cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y nang ((tai hoi) or (tai khoi)). ((hieu ve) OR (hieu va)) tham thuc va hanh dai cua te".
• Adding a wildcard symbol may retrieve word variants: su sach y nang ((tai hoi) or (tai khoi)). ((hieu ve) OR (hieu va)) tham thuc va hanh dai cua te*.