Perhaps you should try some spelling variations:
vat hinh » vat chinh, vat sinh, bat hinh
tu sach » thu sach, su sach, tu cach
te sach » toc sach
hieu ve » hieu va, hieu van
ve pham » vi pham, v pham, ve phan
duc vat » duc va, duy vat, duc van
y nang » ky nang, ly nang, v nang
o hoi » co hoi, o hai, o hoa
o hoc » co hoc, mo hoc, so hoc
su va » su van, tu va
thiet » thieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((tu sach) or (te sach)) y nang ((o hoi) OR (o hoc)). hieu ve pham duc vat hinh su va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (te sach)) y nang ((o hoi) OR (o hoc)). hieu ve pham duc vat hinh su va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (te sach)) y nang ((o hoi) OR (o hoc)). hieu ve pham duc vat hinh su va thiet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (te sach)) y nang ((o hoi) OR (o hoc)). hieu ve pham duc vat hinh su va thiet*.