TRANSFORM Max(experiment.y3) AS Max_y3
SELECT experiment.t
FROM experiment
GROUP BY experiment.t
PIVOT experiment.modelid;

procedure TForm1.Button1Click(Sender: TObject);
var
str:string;
begin
.............

// выбор i

if ADOQuery1.Active then ADOQuery1.Close;

ADOQuery1.SQL.Clear;
str:='TRANSFORM Max(experiment.y'+IntToStr(i)+') AS Max_y3';
ADOQuery1.SQL.Assign(memo1.Lines);       
form1.ADOQuery1.SQL.Strings[ 0 ]:=str;
ADOQuery1.Open;

end;

str:='TRANSFORM Max(experiment.y'+IntToStr(i)+') AS Max_y3';