Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
toc sach » hoc sach, doc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam thu
dang hai » dang khai, hang hai, dung hai
dan hai » doan hai, dan khai, van hai
thuc va » thuc vat, thuc dan, thuc day
cua tre » cua te, cuu tre, cua triet
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
ky lang » ky nang, ky dang, ky tang
va nam » van nam, ha nam, va nay

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