Perhaps you should try some spelling variations:
nghien chua » nghien cuu, nghiep cua, nghiem thuat
chua tinh » cua tinh, cha tinh, thuat tinh
sach doi » sach hoi, sach moi, sach dao
tinh hoc » sinh hoc, tin hoc, hinh hoc
hoc toan » hoc tan, hop toan, hoa toan
khoa hoc » hoa hoc
nhan dan » gian dan, nhan tai
phan dau » phan tu, hang dau
co sach » bo sach, cuon sach, hoc sach
doi tap » doi tac, doi dap, doi tai
hai van » thai van, ha van, hai tan
ma hai » ta hai, va hai, xa hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: co sach doi tap, nghien chua tinh hoc toan khoa hoc ma hai van ((nhan dan) or (phan dau))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: co sach doi tap, nghien chua tinh hoc toan khoa hoc ma hai van ((nhan dan) OR (phan dau)).
• Adding a wildcard symbol may retrieve word variants: co sach doi tap, nghien chua tinh hoc toan khoa hoc ma hai van ((nhan dan) or (phan dau))*.