ORA-01036: Illegal variable name/number

When writing a program today, insert binary data into Oracle, error ORA-01036: Illegal variable name/number, code is as follows:

strSQL = "INSERT into KA99 (ka991,ka992,ka994,ka995,ka997,ka998) VALUES (@KA991, @KA992, @KA994, @KA995, @KA997, @KA998)";

list<oracleparameter> parameters = new list<oracleparameter> ();
Parameters. ADD (New OracleParameter ("@KA991", "1"));
Parameters. ADD (New OracleParameter ("@KA992", this. Versionnumbertextbox.text));
Parameters. ADD (New OracleParameter ("@KA994", Loginuser.name));
Parameters. ADD (New OracleParameter ("@KA995", GetLocalIpv4 ()));
Parameters. ADD (New OracleParameter ("@KA997", Bprogram));
Parameters. ADD (New OracleParameter ("@KA998", this. Remarktextbox.text));

Always error ORA-01036: illegal variable name/number

Find a solution after testing on-line

strSQL = "INSERT into KA99 (ka991,ka992,ka994,ka995,ka997,ka998) VALUES (: ka991,:ka992,:ka994,:ka995,:ka997,:ka998)";

byte[] Bprogram = Stziptoarray (this. Filepathtextbox.text);
list<oracleparameter> parameters = new list<oracleparameter> ();
Parameters. ADD (New OracleParameter ("KA991", "1"));
Parameters. ADD (New OracleParameter ("KA992", this. Versionnumbertextbox.text));
Parameters. ADD (New OracleParameter ("KA994", Loginuser.name));
Parameters. ADD (New OracleParameter ("KA995", GetLocalIpv4 ()));
Parameters. ADD (New OracleParameter ("KA997", Bprogram));
Parameters. ADD (New OracleParameter ("KA998", this. Remarktextbox.text));

ORA-01036: Illegal variable name/number