Perhaps you should try some spelling variations:
cach thuc » anh thuc, cac thu
cac thuc » cac thu, can thuc, cay thuc
thanh vi » thanh va, thanh ve, nhanh vi
su sach » so sach, vu sach
su viet » so viet
sach ty » sach y, sach tu, sach thu
hieu ve » hieu va, hieu van
xang o » lang o, tang o, dang o
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: su sach ty xang o hoi. hieu ve ((cac thuc) OR (cach thuc)) va ((thanh vi) or (hanh vi)) su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ty xang o hoi. hieu ve ((cac thuc) OR (cach thuc)) va ((thanh vi) OR (hanh vi)) su viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ty xang o hoi. hieu ve ((cac thuc) OR (cach thuc)) va ((thanh vi) or (hanh vi)) su viet".
• Adding a wildcard symbol may retrieve word variants: su sach ty xang o hoi. hieu ve ((cac thuc) OR (cach thuc)) va ((thanh vi) or (hanh vi)) su viet*.