Perhaps you should try some spelling variations:
cua viet » ca viet, hoa viet, cua vat
thue va » thuc va, thuyet va, thuc vat
sach ty » sach y, sach tu, sach thu
so sach » so sanh, bo sach, co sach
ty tang » tay tang, ty xang, ty hang
hieu he » hieu ve, hiem he, hieu le
ma hoi » mai hoi, ma hoa, me hoi
he nam » ha nam, nghe nam
thu va » thuc va, tu va, thu ha
vi cua » vai cua, di 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 hoi) or (xa hoi)). hieu he nam ((thu va) OR (thue va)) hanh vi cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ty tang ((ma hoi) OR (xa hoi)). hieu he nam ((thu va) OR (thue va)) hanh vi cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ty tang ((ma hoi) or (xa hoi)). hieu he nam ((thu va) OR (thue va)) hanh vi cua viet".
• Adding a wildcard symbol may retrieve word variants: so sach ty tang ((ma hoi) or (xa hoi)). hieu he nam ((thu va) OR (thue va)) hanh vi cua viet*.