Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cap nuoc » dat nuoc
cac nuoc » hoc nuoc, dat nuoc, cua nuoc
hieu van » hieu va, thien van, lieu va
ky tang » ky nang, ky dang, kho tang
ky sang » ky nang, ky dang, duy sang
ma hoi » mai hoi, xa hoi, ma hoa
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan va
vi cau » va cau, ve cau, di cau

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 sang) or (ky tang)) ma hoi. hieu van ((cac nuoc) OR (cap nuoc)) va dan vi cau tao~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky sang) OR (ky tang)) ma hoi. hieu van ((cac nuoc) OR (cap nuoc)) va dan vi cau tao.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky sang) or (ky tang)) ma hoi. hieu van ((cac nuoc) OR (cap nuoc)) va dan vi cau tao".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky sang) or (ky tang)) ma hoi. hieu van ((cac nuoc) OR (cap nuoc)) va dan vi cau tao*.