Springer have made a bunch of books available for free, here are the direct links · GitHub

#!/usr/bin/python
import os, re
import requests
regexp = re.compile("\((http://[^\)]+)\)")
r = requests.get('https://gist.github.com/bishboria/8326b17bbd652f34566a/raw/c20ec05dc4669b93f16d0b5c5824615dea42a956/springer-free-maths-books.md')
for line in map(lambda x: x.strip(), r.content.split(os.linesep)):
match = regexp.search(line)
if match:
url = match.groups()[0]
fname = url.split('/')[-1]
print fname
r = requests.get(url)
if r is not None:
with open(fname, 'w') as ofp:
ofp.write(r.content)