Perhaps you should try some spelling variations:
cach thuc » anh thuc, cac thu
cac thoi » cac toi, cac hop, cac tro
sach ky » sach y, sach ty, sach kem
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
sac ky » cac ky, sai ky
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va
vi cua » vai cua, di cua
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu ((sach ky) OR (sac ky)) nang o hoi. hieu ve ((cac thoi) or (cach thuc)) va dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sac ky)) nang o hoi. hieu ve ((cac thoi) OR (cach thuc)) va dan vi cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) OR (sac ky)) nang o hoi. hieu ve ((cac thoi) or (cach thuc)) va dan vi cua tre*".