Perhaps you should try some spelling variations:
van thiet » va thiet, dan thiet, can thiet
tinh voi » trinh voi, binh voi, minh voi
tinh doi » trinh doc, trinh do, tinh hoc
su sach » so sach, vu sach
hieu ve » hieu va, hieu van
cac bac » cac bai, cac ban, cac cach
bac may » ban may, bach mai, bac thay
tinh vi » trinh vi, tinh va, dinh vi
y nang » ky nang, ly nang, v nang
ve cac » va cac, vien cac
x hoi » xa hoi, o hoi, x ho

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 y nang x hoi. hieu ve cac bac may ((tinh vi) or (((tinh voi) OR (tinh doi)))) van thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang x hoi. hieu ve cac bac may ((tinh vi) OR (((tinh voi) OR (tinh doi)))) van thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y nang x hoi. hieu ve cac bac may ((tinh vi) or (((tinh voi) OR (tinh doi)))) van thiet".
• Adding a wildcard symbol may retrieve word variants: su sach y nang x hoi. hieu ve cac bac may ((tinh vi) or (((tinh voi) OR (tinh doi)))) van thiet*.