Perhaps you should try some spelling variations:
nam thuat » nam thuan, tam thuat, nam thu
thuat vat » thuat va, thuc vat, thuat xay
vat hanh » vat thanh, van hanh, va hanh
khoa hoi » khoan hoi, khoa hoc, khoa doi
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
hieu he » hieu ve, hiem he, hieu le
hoa hoi » hoa hoc, hoa doi, hoc hoi
ky dang » ky nang, ky danh
tai va » thai va, mai va, dai va
he nam » ha nam, nghe nam

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach ky dang ((hoa hoi) or (khoa hoi)). hieu he nam thuat vat hanh ((tai va) OR (tri va)) triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky dang ((hoa hoi) OR (khoa hoi)). hieu he nam thuat vat hanh ((tai va) OR (tri va)) triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky dang ((hoa hoi) or (khoa hoi)). hieu he nam thuat vat hanh ((tai va) OR (tri va)) triet".
• Adding a wildcard symbol may retrieve word variants: su sach ky dang ((hoa hoi) or (khoa hoi)). hieu he nam thuat vat hanh ((tai va) OR (tri va)) triet*.