private void button3_Click(object sender, EventArgs e)
        {
            Excel.Application excel = new Excel.Application();
            System.Diagnostics.Process.Start("Book1.xls");
            excel.Visible = false;
            string k1 = textBox4.Text;
            float a1 = float.Parse(k1);
            excel.Cells[3, 3] =a1;
            string a2 = excel.Cells[3, 4].ToString();
            textBox8.Text = a2;
            excel.Workbooks[1].SaveCopyAs("Book1.xls");//保存
        }