Twitter Api Call fetch users timeline error 400 bad request error

i am using the following code to fetch tweets from user timeline .but in response it gives error bad request in all api calls that i am making

   public string query = "nouman_engineer";

     public string url = "http://ift.tt/1IdLU4E";


    public void findUserTwitter(string resource_url, string q)
{

    // oauth application keys
    var oauth_token = pass; //"insert here...";
    var oauth_token_secret = pass; //"insert here...";
    var oauth_consumer_key = "pass";
        var oauth_consumer_secret = "pass";

    // oauth implementation details
    var oauth_version = "1.1";
    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();

    var screen_name = "nouman_engineer";
    // create oauth signature
    var baseFormat = "count=1&exclude_replies=1&include_entities=false&include_rts=false&oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}&screen_name={6}&trim_user=1";
    var baseString = string.Format(baseFormat,
                                oauth_consumer_key,
                                oauth_nonce,
                                oauth_signature_method,
                                oauth_timestamp,
                                oauth_token,
                                oauth_version,
                                 Uri.EscapeDataString(screen_name)
                                );


    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)
                    );



    ServicePointManager.Expect100Continue = false;

    // make the request
    var postBody = "q=" + Uri.EscapeDataString(q);//
    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";

ERROR HERE The remote server returned an error: (400) Bad Request.

            var response = (HttpWebResponse)request.GetResponse();

///////IN CASE OF RESPONSE

          var reader = new StreamReader(response.GetResponseStream());
         var objText = reader.ReadToEnd();
          myDiv.InnerHtml = objText;/**/
    string html = "";
    try
    {
        JArray jsonDat = JArray.Parse(objText);
        for (int x = 0; x < jsonDat.Count; x++)
        {
            //html += jsonDat[x]["id"].ToString() + "<br/>";
            html += jsonDat[x]["text"].ToString() + "<br/>";
           // html += jsonDat[x]["name"].ToString() + "<br/>";
            html += jsonDat[x]["created_at"].ToString() + "<br/>";

        }
        myDiv.InnerHtml = html;
    }
    catch (Exception twit_error)
    {
        myDiv.InnerHtml = html + twit_error.ToString();
    }

WHAT SHOULD I DO KINDLY GUIDE ME