Perhaps you should try some spelling variations:
pham duy » pham duc
van hanh » van thanh, ban hanh, van anh
so sach » so sanh, bo sach, co sach
sach ty » sach y, sach tu, sach thu
tang ma » tang van
hieu vu » hieu va, hieu ve, hieu su
vu pham » su pham, vi pham, vu kham
duy van » duy vat, dung van
hanh va » hang va, hanh vi
cua tre » cua te, cuu tre, cua triet
va cua » va chua, via cua, ca cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ty ((tang ma) or (mang may)) hoi. hieu vu pham duy van hanh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ty ((tang ma) OR (mang may)) hoi. hieu vu pham duy van hanh va cua tre.
• Adding a wildcard symbol may retrieve word variants: so sach ty ((tang ma) or (mang may)) hoi. hieu vu pham duy van hanh va cua tre*.