Perhaps you should try some spelling variations:
cau thuc » cau truc, cuu thuc, can thuc
dieu tra » dieu tri, kiem tra, dieu cua
ban hanh » ban hang
van hanh » van thanh, van anh, van ban
tra tre » tran tren, tran tri, tran tro
sach ky » sac ky, sach ty, sach kem
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
ma hoi » mai hoi, xa hoi, ma hoa
va cau » van cau, va cac, va dau

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: te ((sach ky) OR (sach y)) nang ma hoi. hieu va cau thuc ((van hanh) OR (ban hanh)) dieu tra tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ky) or (sach y)) nang ma hoi. hieu va cau thuc ((van hanh) OR (ban hanh)) dieu tra tre~".
• Adding a wildcard symbol may retrieve word variants: te ((sach ky) or (sach y)) nang ma hoi. hieu va cau thuc ((van hanh) OR (ban hanh)) dieu tra tre*.