Hi, and welcome.
Could you post this as a reproducible example, called a reprex, please. That makes it a lot easier to troubleshoot. Here's an example based on the vignette
library(bibliometrix)
#> To cite bibliometrix in publications, please use:
#>
#> Aria, M. & Cuccurullo, C. (2017) bibliometrix: An R-tool for comprehensive science mapping analysis, Journal of Informetrics, 11(4), pp 959-975, Elsevier.
#>
#>
#> http:\\www.bibliometrix.org
#>
#>
#> To start with the shiny web-interface, please digit:
#> biblioshiny()
D <- readFiles("https://www.bibliometrix.org/datasets/savedrecs.bib")
M <- convert2df(D, dbsource = "isi", format = "bibtex")
#>
#> Converting your isi collection into a bibliographic dataframe
#>
#> Articles extracted 100
#> Articles extracted 200
#> Articles extracted 291
#> Done!
#>
#>
#> Generating affiliation field tag AU_UN from C1: Done!
M$CR[1]
#> [1] "[ANONYMOUS], 2013, GUARDIAN.;KETEFIAN S, 2009, INT J NURS STUD, V46, P751, DOI 10.1016/J.IJNURSTU.2008.08.009.;STEFANIAK B, 2001, SCIENTOMETRICS, V52, P193, DOI 10.1023/A:1017959605687.;FITZPATRICK JJ, 2013, APPL NURS RES, V26, P49, DOI 10.1016/J.APNR.2013.02.002.;POLIT DF, 2011, NURS OUTLOOK, V59, P18, DOI 10.1016/J.OUTLOOK.2010.11.001.;LEE S, 2005, SOC STUD SCI, V35, P673, DOI 10.1177/0306312705052359.;CLARK AM, 2012, J ADV NURS, V68, P2373, DOI 10.1111/J.1365-2648.2012.06081.X.;GALLAGHER A, 2011, NURS ETHICS, V18, P3, DOI 10.1177/0969733010388353.;SMITH DR, 2011, NURS HEALTH SCI, V13, P384, DOI 10.1111/J.1442-2018.2011.00652.X.;VAUGHAN L, 2005, J AM SOC INF SCI TEC, V56, P1075, DOI 10.1002/ASI.20199.;JOHNSTONE MJ, 2007, INT NURS REV, V54, P35, DOI 10.1111/J.1466-7657.2007.00527.X.;DE GROOTE SL, 2012, NURS OUTLOOK, V60, P391, DOI 10.1016/J.OUTLOOK.2012.04.007.;CLARK A.M., 2015, J ADV NURS, V71, P1.;MOLZAHN AE, 2015, NURS EDUC TODAY, V35, P9, DOI 10.1016/J.NEDT.2014.07.004.;THOMSON P, 2006, HELPING DOCTORAL STU."
Created on 2019-11-28 by the reprex package (v0.3.0)