推特api V1.1-获取“；(401)未经授权的“；当试图获取user_timeline时

我正在尝试使用ASP.NET从twitter api v1.1获取用户时间线，除非我添加count参数，否则它运行良好。我的代码如下；

string oauth_token = "xxx";
    string oauth_token_secret = "xxx";
    string oauth_consumer_key = "xxx";
    string oauth_consumer_secret = "xxx";
    public string GetUserTimeline(string userName, int tweetCount)
    {
        // oauth implementation details
        var oauth_version = "1.0";
        var oauth_signature_method = "HMAC-SHA1";
        // unique request details
        var oauth_nonce = Convert.ToBase64String(
            new ASCIIEncoding().GetBytes(DateTime.Now.Ticks.ToString()));
        var timeSpan = DateTime.UtcNow
            - new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
        var oauth_timestamp = Convert.ToInt64(timeSpan.TotalSeconds).ToString();
        // message api details
        var status = "Updating status via REST API if this works";
        var resource_url = "https://api.twitter.com/1.1/statuses/user_timeline.json";
        // create oauth signature
        var baseFormat = "oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}" +
                        "&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}&screen_name={6}";
        var baseString = string.Format(baseFormat,
                                    oauth_consumer_key,
                                    oauth_nonce,
                                    oauth_signature_method,
                                    oauth_timestamp,
                                    oauth_token,
                                    oauth_version,
                                     Uri.EscapeDataString(userName)
                                    );
        baseString = string.Concat("GET&", Uri.EscapeDataString(resource_url), "&", Uri.EscapeDataString(baseString));
        var compositeKey = string.Concat(Uri.EscapeDataString(oauth_consumer_secret),
                                "&", Uri.EscapeDataString(oauth_token_secret));
        string oauth_signature;
        using (HMACSHA1 hasher = new HMACSHA1(ASCIIEncoding.ASCII.GetBytes(compositeKey)))
        {
            oauth_signature = Convert.ToBase64String(
                hasher.ComputeHash(ASCIIEncoding.ASCII.GetBytes(baseString)));
        }
        // create the request header
        var headerFormat = "OAuth oauth_nonce='"{0}'", oauth_signature_method='"{1}'", " +
                           "oauth_timestamp='"{2}'", oauth_consumer_key='"{3}'", " +
                           "oauth_token='"{4}'", oauth_signature='"{5}'", " +
                           "oauth_version='"{6}'"";
        var authHeader = string.Format(headerFormat,
                                Uri.EscapeDataString(oauth_nonce),
                                Uri.EscapeDataString(oauth_signature_method),
                                Uri.EscapeDataString(oauth_timestamp),
                                Uri.EscapeDataString(oauth_consumer_key),
                                Uri.EscapeDataString(oauth_token),
                                Uri.EscapeDataString(oauth_signature),
                                Uri.EscapeDataString(oauth_version)
                        );

        // make the request
        ServicePointManager.Expect100Continue = false;
        var postBody = "screen_name=" + Uri.EscapeDataString(userName);//
        resource_url += "?" + postBody;
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(resource_url);
        request.Headers.Add("Authorization", authHeader);
        request.Method = "GET";
        request.ContentType = "application/x-www-form-urlencoded";

        WebResponse response = request.GetResponse();
        string responseData = new StreamReader(response.GetResponseStream()).ReadToEnd();
        return responseData.ToString();
    }

问题是，当我添加count参数来限制推特的数量时，我会收到"（401）未授权"错误。以下是带参数的版本；

var baseFormat = "count=25&oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}" +
                       "&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}&screen_name={6}";
var postBody = "count=25&screen_name=" + Uri.EscapeDataString(userName);

我做错了什么？