Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
hieu van » hieu va, thien van, lieu va
dat van » dao van, dat va, dam van
cau dat » cai dat, cau hat, chap dat
van cau » van dau, van hau, van chat
tang ma » mang may, tang van
sach ky » sac ky, sach ty, sach kem
nang ma » sang ma, nang cao, mang may
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: thuat ((sach ky) or (sach y)) ((nang ma) or (tang ma)) hoi. hieu van cau dat van hanh vi cua vat~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuat ((sach ky) OR (sach y)) ((nang ma) OR (tang ma)) hoi. hieu van cau dat van hanh vi cua vat.
• Adding a wildcard symbol may retrieve word variants: thuat ((sach ky) or (sach y)) ((nang ma) or (tang ma)) hoi. hieu van cau dat van hanh vi cua vat*.