library(XML)

xmlfile2 <- xmlTreeParse("pubmed_result.xml")

# Use the xmlRoot-function to access the top node
xmltop2 <- xmlRoot(xmlfile2)
xmlName(xmltop2) # root is an article set
# have a look at the XML-code of the first subnodes:
num_articles <- xmlSize(xmltop2)
xmlName(xmltop2[[1]]) # Pub med article
xmltop2[[1]] # retrieve the pubmed article

xmlName(xmltop2[[1]][[2]]) # "PubmedData"
xmltop2[[1]][[2]] # pubmed data
xmlName(xmltop2[[1]][[2]][[1]]) #History element
xmltop2[[1]][[2]][[1]] # History element
xmlName(xmltop2[[1]][[2]][[1]][[1]]) #PubMedPubDate
xmltop2[[1]][[2]][[1]][[1]] # History element