Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
danh dai » danh dau, danh di, danh sai
ky sang » ky nang, ky tang, duy sang
ky dang » ky nang, ky danh
hieu ve » hieu va, hieu van
ve pham » vi pham, v pham, ve phan
va danh » va dinh, va dan, va hanh
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) or (toc sach)) ((ky sang) OR (ky dang)) ma hoi. hieu ve pham duc va danh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ((ky sang) OR (ky dang)) ma hoi. hieu ve pham duc va danh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) ((ky sang) OR (ky dang)) ma hoi. hieu ve pham duc va danh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ((ky sang) OR (ky dang)) ma hoi. hieu ve pham duc va danh dai cua tre*.