install.packages("httr")
install.packages("xml2")
library(httr)
library(xml2)
baseUrl="https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esearch.fcgi?"
searchArticleParam=list(retstart=0,retmax=20,usehistory='Y',querykey='',webenv='',term='(cell[TA]) AND 2017[DP]',total_num=0,total_page=1, page_size=20, current_page=1)
r<-POST(baseUrl,body=list(db='pubmed',term=searchArticleParam$term,retmode='json',retstart=searchArticleParam$retstart,retmax=searchArticleParam$retmax,usehistory=searchArticleParam$usehistory,
                          rettype='uilist'))
stop_for_status(r)
data=content(r, "parsed","application/json")
data
esearchresult=data$esearchresult
count=esearchresult$count
print(count)

baseUrl2="https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?"
pubmedid="29275861,29275860";
searchArticleParam$total_num=esearchresult$count
searchArticleParam$querykey=esearchresult$querykey
searchArticleParam$webenv=esearchresult$webenv
r2<-POST(baseUrl2,body=list(db='pubmed',id=pubmedid,retmode='xml',querykey=searchArticleParam$querykey,webenv=searchArticleParam$webenv))
data2=content(r2,"parsed")
article=xml_children(data2)
count=length(article)
cnt=1
while(cnt<=count){title=xml_find_first(article[cnt],".//ArticleTitle")
abstract=xml_find_first(article[cnt],".//AbstractText")
print(xml_text(title))
print(xml_text(abstract))
cnt = cnt + 1
}

真心不会做，特别是第一题的解析部分，基本是全部抄了R2-01才出来了个563，自己的代码一直是NULL