Perhaps you should try some spelling variations:
cam thuc » nam thuc, cam thu, can thuc
danh tai » doanh tai, dinh tai, hanh tai
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
va danh » va dinh, va dan, va hanh
cuc tre » duc tre, cua tre, cuu tre
y nang » ly nang, v nang, may nang
o hoi » co hoi, o hoc, o hai

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

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((y nang) OR (ky nang)) o hoi. hieu ve ((cam thuc) OR (am thuc)) va danh tai cuc tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((y nang) OR (ky nang)) o hoi. hieu ve ((cam thuc) or (am thuc)) va danh tai cuc tre~".
• Adding a wildcard symbol may retrieve word variants: tu sach ((y nang) OR (ky nang)) o hoi. hieu ve ((cam thuc) or (am thuc)) va danh tai cuc tre*.