Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
vat hinh » vat chinh, vat sinh, bat hinh
tu sach » thu sach, su sach, tu cach
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
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai
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) OR (toc sach)))) y nang o hoi. 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) OR (toc sach)))) y nang o hoi. 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) OR (toc sach)))) y nang o hoi. hieu ve pham duc vat hinh su va thiet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (((te sach) OR (toc sach)))) y nang o hoi. hieu ve pham duc vat hinh su va thiet*.