Perhaps you should try some spelling variations:
cua viet » ca viet, hoa viet, cua vat
sach ty » sach y, sach tu, sach thu
hieu va » lieu va, hieu qua
truc va » thuc va, trung va
hanh va » hang va, hanh vi
sai ky » sac ky
va cau » van cau, va cac, va dau
va cua » va chua, via cua, ca cua
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: tu ((sach ty) or (sai ky)) nang x hoi. hieu va cau ((truc va) OR (thuc vat)) hanh va cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ty) OR (sai ky)) nang x hoi. hieu va cau ((truc va) OR (thuc vat)) hanh va cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ty) or (sai ky)) nang x hoi. hieu va cau ((truc va) OR (thuc vat)) hanh va cua viet".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ty) or (sai ky)) nang x hoi. hieu va cau ((truc va) OR (thuc vat)) hanh va cua viet*.