Perhaps you should try some spelling variations:
gia doanh » gia thanh, gia dinh, giai doan
duc gia » quoc gia
lam duc » lam duoc, pham duc, nam duoc
sach ky » sac ky, sach y, sach kem
so viet » hoc viet
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
sach ty » sach y, sach tu, sach thu
va lam » van lam, va lap

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach ky) or (sach ty)) nang ma hoa. hieu va lam duc gia doanh tai ((su viet) OR (so viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach ty)) nang ma hoa. hieu va lam duc gia doanh tai ((su viet) OR (so viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sach ty)) nang ma hoa. hieu va lam duc gia doanh tai ((su viet) OR (so viet))".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sach ty)) nang ma hoa. hieu va lam duc gia doanh tai ((su viet) OR (so viet))*.