Perhaps you should try some spelling variations:
nang mai » nang ma, lang mai, nang cai
nang tai » hang tai, tang tai, sang tai
hieu van » hieu va, thien van, lieu va
cam duc » cam xuc, cao duc, nam duoc
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
san ky » sang ky, van ky, dan ky
vi cua » vai cua, di cua
phi » phai

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

• Performing a fuzzy search may retrieve terms with similar spellings: phi san ky ((nang mai) or (nang tai)) hoi. hieu van ((cam duc) OR (pham duc)) va hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: phi san ky ((nang mai) OR (nang tai)) hoi. hieu van ((cam duc) OR (pham duc)) va hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "phi san ky ((nang mai) or (nang tai)) hoi. hieu van ((cam duc) OR (pham duc)) va hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: phi san ky ((nang mai) or (nang tai)) hoi. hieu van ((cam duc) OR (pham duc)) va hanh vi cua tre*.