Perhaps you should try some spelling variations:
chat hoc » chat thom, cho hoc, vat hoc
chat hoa » thuat hoa, chat va, chat huu
tu sach » thu sach, su sach, te sach
hanh va » hang va, hanh vi
thuc va » thuc vat, thuc dan, thuc day
hieu ve » hieu va, hieu van
ve cham » va cham, ve chat, vu cham
sach ty » sach y, sach tu, sach thu
ty nang » ky nang, ty xang, ty hang
tuc va » truc va, tuc xa, duc va
va va » va van, va vua, va vai
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 ty nang ((chat hoc) OR (chat hoa)). hieu ve cham ((tuc va) or (thuc va)) hanh va va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty nang ((chat hoc) OR (chat hoa)). hieu ve cham ((tuc va) OR (thuc va)) hanh va va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty nang ((chat hoc) OR (chat hoa)). hieu ve cham ((tuc va) or (thuc va)) hanh va va thiet".
• Adding a wildcard symbol may retrieve word variants: tu sach ty nang ((chat hoc) OR (chat hoa)). hieu ve cham ((tuc va) or (thuc va)) hanh va va thiet*.