C#后台无刷新页面弹出alert方法

无刷新弹出警告：       

ScriptManager.RegisterStartupScript(this.Page, this.GetType(),"onekey", "alert('弹出')", true);

而以下方法，会刷新弹出，比较难看

Response.Write("<script>alert('弹出')</script>");

ClientScript.RegisterStartupScript(this.Page, this.GetType(),"onekey", "alert('弹出')", true);