Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, mang xa
nang ma » tang ma, sang ma, nang cao
van cau » van dau, van hau, van chat
cua tre » cua te, cuu tre, cua triet
xuc va » tuc va, luc va, xac va
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: toc sach ky ((nang xa) or (nang ma)) hoi. hieu van cau ((xuc va) OR (duc va)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((nang xa) OR (nang ma)) hoi. hieu van cau ((xuc va) OR (duc va)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky ((nang xa) or (nang ma)) hoi. hieu van cau ((xuc va) OR (duc va)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky ((nang xa) or (nang ma)) hoi. hieu van cau ((xuc va) OR (duc va)) hanh vi cua tre*.