import requests ## url, strony www
import wget   ## adresy url
import bs4

listaLinkow = list()
listaPDF= list()

url = 'https://bmcsystbiol.biomedcentral.com/articles'
page = requests.get(url,verify=True).text
soup = bs4.BeautifulSoup(page,'html.parser')

# wyszukiwanie linków do podstron
for link in soup.find_all('li',{'class':'c-list-group__item'}):
    for plink in link.find_all('a'):
        if ('/articles/' in plink.get('href')):
            listaLinkow.append('https://bmcsystbiol.biomedcentral.com' + plink.get('href'))

# grzebanie w podstronie nr 1

for i in range(0,2):
    url = listaLinkow[i]
    page = requests.get(url,verify=True).text
    soup = bs4.BeautifulSoup(page,'html.parser')
    for link in soup.find_all('a',{'id':'articlePdf'}):
        listaPDF.append('https:'+link.get('href'))

print(listaPDF)
for i in listaPDF:
    wget.download(i,'.pdf')