uld="http://link.springer.com/content/"+res.data.decode('utf-8').split('Download book PDF')[0].split('content/')[1].split('title')[0].split('.pdf')[0]+".pdf"
dl_url="https://link.springer.com/content/"+res.data.decode('utf-8').split('Download book PDF')[0].split('content/')[1].split('title')[0].split('.pdf')[0]+".pdf"