Perhaps you should try some spelling variations:
va tinh » may tinh
va dinh » van dinh, va kinh, vu dinh
sach ky » sac ky, sach ty, sach kem
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
su viet » so viet
ma hoi » mai hoi, xa hoi, ma hoa
va dam » van dam, va dao, va dau
dam tu » nam tu, cam tu, tam tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc ((sach ky) or (sach y)) nang ma hoi. hieu va dam tu ((va dinh) OR (va tinh)) va su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc ((sach ky) OR (sach y)) nang ma hoi. hieu va dam tu ((va dinh) OR (va tinh)) va su viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc ((sach ky) or (sach y)) nang ma hoi. hieu va dam tu ((va dinh) OR (va tinh)) va su viet".
• Adding a wildcard symbol may retrieve word variants: toc ((sach ky) or (sach y)) nang ma hoi. hieu va dam tu ((va dinh) OR (va tinh)) va su viet*.