I felt it difficult to download spec files one by one.
Here is script to download it at once.
import requests
for i in ['401', '410', '411', '412', '413', '414', '420', '421', '422', '423', '424', '425', '440', '441', '442', '443', '444', '445', '455', '456', '457', '458', '459', '461', '462', '463', '464', '465']:
#for i in "range(400,499)":
file_url = "https://www.etsi.org/deliver/etsi_ts/136400_136499/136" + i + "/15.00.00_60/ts_136" + i + "v150000p.pdf"
file_name = "36." + i + "_150000p.pdf"
#print("wget", file_url)
r = requests.get(file_url, stream = True)
with open(file_name,"wb") as pdf:
for chunk in r.iter_content(chunk_size=1024):
#writing one chunk at a time to pdf file
if chunk:
pdf.write(chunk)