public string GetBookSearchUrl()
{
string searchUrl = "";
searchUrl += searchBaseUrl;
searchUrl += "?";
searchUrl += "q=" + searchKey;
searchUrl += "&start-index=" + (inc_results * search_times + 1).ToString();
searchUrl += "&max-results=" + ((search_times+1) * inc_results).ToString();
search_times++;
searchUrl += "&apikey=" + apiKey;
return searchUrl;
}