Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam tu
ky lang » ky nang, ky tang, tay lang
ky dang » ky nang, ky danh
dan dai » dat dai, can dai, dan dat
cua tre » cua te, cuu tre, cua triet
va dan » ca dan, va dao, va dau

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 lang) OR (ky dang)) xa hoi. lieu va ((nam thuc) or (nam thu)) va dan dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky dang)) xa hoi. lieu va ((nam thuc) OR (nam thu)) va dan dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) OR (ky dang)) xa hoi. lieu va ((nam thuc) or (nam thu)) va dan dai cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) OR (ky dang)) xa hoi. lieu va ((nam thuc) or (nam thu)) va dan dai cua tre*.