Perhaps you should try some spelling variations:
va thanh » gia thanh, ban thanh, va tinh
nang xa » nang x, lang xa, nang ma
hieu va » lieu va, hieu qua
cac hoc » cach hoc, cac hop, bac hoc
va hanh » van hanh, va danh, ban hanh
cua tre » cua te, cuu tre, cua triet
san ky » sang ky, van ky, ban ky
dan ky » van ky
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: thu ((san ky) OR (dan ky)) nang xa hoi. hieu va cac hoc ((va hanh) or (va thanh)) vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu ((san ky) OR (dan ky)) nang xa hoi. hieu va cac hoc ((va hanh) OR (va thanh)) vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu ((san ky) OR (dan ky)) nang xa hoi. hieu va cac hoc ((va hanh) or (va thanh)) vi cua tre".
• Adding a wildcard symbol may retrieve word variants: thu ((san ky) OR (dan ky)) nang xa hoi. hieu va cac hoc ((va hanh) or (va thanh)) vi cua tre*.