Dear all,

I want to run some regressions with year, industry and country fixed effects. However, I would like to include a time trend in each regression. The process goes as follows, I want to estimate how the shares of employment in high tech industries are explained by the level of human capital within the country. My data is:

Code:
 * Example generated by -dataex-. To install: ssc install dataex
clear
input float country1 int year str2 isic float tech_intensity long Employment float(share_emp hc)
8 1985 "15" 1     .           . 2.2555776
8 1986 "15" 1     .           .   2.30544
8 1987 "15" 1     .           . 2.3564048
8 1988 "15" 1 28488     .124983  2.408496
8 1989 "15" 1 33285   .13802098  2.461739
8 1990 "15" 1 34191   .13564035  2.516159
8 1993 "15" 1 15100    .2557978 2.5148826
8 1994 "15" 1  7220    .1970309  2.514457
8 1995 "15" 1  4515    .2089407  2.514032
8 1996 "15" 1  5836   .24414323 2.5811894
8 1997 "15" 1  8599    .3785937  2.634504
8 1998 "15" 1  4316   .11582224   2.68892
8 1999 "15" 1  4032   .13085386   2.74446
8 2000 "15" 1  3919   .12122993 2.8011475
8 2001 "15" 1  3144   .10250057   2.81509
8 2002 "15" 1  3790   .10898948 2.8291016
8 2003 "15" 1  3965   .10707534  2.843183
8 2004 "15" 1  4599   .12050308  2.857335
8 2005 "15" 1  5230   .13512117  2.871557
8 2006 "15" 1  5503   .13065362  2.878032
8 2007 "15" 1  6532   .13651279 2.8845215
8 2008 "15" 1  6243    .1298569 2.8910255
8 2009 "15" 1  6832   .14407423 2.8975446
8 2010 "15" 1  7208   .13335307  2.904078
8 2011 "15" 1  7804   .14119776 2.9106934
8 2012 "15" 1  8202   .14464334  2.917346
8 2013 "15" 1  8784   .14344972  2.924037
8 2014 "15" 1  8970   .13227747  2.930766
8 2015 "15" 1 11287   .15261777 2.9375334
8 2016 "15" 1 14582   .16869505  2.944339
8 2017 "15" 1 15307   .16537024  2.951184
8 2018 "15" 1 16373    .1655996 2.9580684
8 2019 "15" 1 17426    .1656039  2.964992
8 1985 "16" 1     .           . 2.2555776
8 1986 "16" 1     .           .   2.30544
8 1987 "16" 1     .           . 2.3564048
8 1988 "16" 1     .           .  2.408496
8 1989 "16" 1     .           .  2.461739
8 1990 "16" 1     .           .  2.516159
8 1993 "16" 1  2253   .03816639 2.5148826
8 1994 "16" 1  1311  .035776664  2.514457
8 1995 "16" 1   976   .04516637  2.514032
8 1996 "16" 1  2148   .08985944 2.5811894
8 1997 "16" 1  1946    .0856778  2.634504
8 1998 "16" 1  1399   .03754294   2.68892
8 1999 "16" 1  1137   .03690001   2.74446
8 2000 "16" 1   899   .02780957 2.8011475
8 2001 "16" 1   546  .017800672   2.81509
8 2002 "16" 1   418  .012020475 2.8291016
8 2003 "16" 1   374  .010099919  2.843183
8 2004 "16" 1   253   .00662911  2.857335
8 2005 "16" 1   240  .006200589  2.871557
8 2006 "16" 1   188 .0044635436  2.878032
8 2007 "16" 1   174 .0036364396 2.8845215
8 2008 "16" 1   147  .003057659 2.8910255
8 2009 "16" 1   123  .002593842 2.8975446
8 2010 "16" 1   185   .00342263  2.904078
8 2011 "16" 1   104  .001881672 2.9106934
8 2012 "16" 1    92  .001622432  2.917346
8 2013 "16" 1   144  .002351635  2.924037
8 2014 "16" 1   273  .004025836  2.930766
8 2015 "16" 1     .           . 2.9375334
8 2016 "16" 1     .           .  2.944339
8 2017 "16" 1     .           .  2.951184
8 2018 "16" 1     .           . 2.9580684
8 2019 "16" 1     .           .  2.964992
8 1985 "17" 1     .           . 2.2555776
8 1986 "17" 1     .           .   2.30544
8 1987 "17" 1     .           . 2.3564048
8 1988 "17" 1 61728   .27081406  2.408496
8 1989 "17" 1 65344   .27095816  2.461739
8 1990 "17" 1 73034   .28973582  2.516159
8 1993 "17" 1  7946   .13460724 2.5148826
8 1994 "17" 1  3338   .09109268  2.514457
8 1995 "17" 1   172  .007959646  2.514032
8 1996 "17" 1   106 .0044344044 2.5811894
8 1997 "17" 1   960   .04226654  2.634504
8 1998 "17" 1 10082   .27055603   2.68892
8 1999 "17" 1  8223   .26686788   2.74446
8 2000 "17" 1  8717   .26965076 2.8011475
8 2001 "17" 1  8562     .279138   2.81509
8 2002 "17" 1 11638    .3346753 2.8291016
8 2003 "17" 1 10479   .28298676  2.843183
8 2004 "17" 1 10213    .2676012  2.857335
8 2005 "17" 1 10018   .25882292  2.871557
8 2006 "17" 1  9807    .2328403  2.878032
8 2007 "17" 1 12639   .26414344 2.8845215
8 2008 "17" 1 13162   .27377486 2.8910255
8 2009 "17" 1 11845    .2497891 2.8975446
8 2010 "17" 1 14105    .2609524  2.904078
8 2011 "17" 1 14172   .25641397 2.9106934
8 2012 "17" 1 15088   .26607883  2.917346
8 2013 "17" 1 15873   .25921872  2.924037
8 2014 "17" 1 18485   .27259186  2.930766
8 2015 "17" 1   981  .013264644 2.9375334
8 2016 "17" 1   991    .0114646  2.944339
8 2017 "17" 1  1449  .015654372  2.951184
8 2018 "17" 1  1943   .01965187 2.9580684
8 2019 "17" 1  2068   .01965275  2.964992
8 1985 "18" 1     .           . 2.2555776
end
I would like to include not only year fixed effects but also a time trend (this shares of employment are expected to follow a linear trend over time). So, far the specifications without time trends go as follows:

Code:
 reg share_emp hc resources i.year i.country1 i.isic1 if tech_intensity==1,robust
Code:
 reg share_emp hc resources i.year i.country1 i.isic1 if tech_intensity==3,robust
How could I include the time trend in these regressions? Thank you!