論文呢 應該根據你寫的內容來決定時態.
如果是描述現在的狀態還是用一般現在時,
但如果是講過去的事情,還是用過去時.
具體你論文什么內容不如跟我說說,幫你具體參謀一下.

用一般過去時, 因為是記述一天已經發生內過的事容情

如: July 1st, sunny

It was Sunday and it was sunny today. I went to the park with my parents. There were thousands of people in the park. Some of them played chess under the big tree. Some of them rowed boat on the lake. We climbed the mountain and had a picnic on the top of the mountain. Then we picked up the rubbish and threw it into the dustbin because it was our duty to protect the environment. Although we felt tired, we were really happy.

日記記得是一天已經發生的事，宜用一般過去式帶完成時（假如對現在產生影響）事實可以用一般現在時
I was very sleepy in the morning, so i didn't go running as usual. I had something for breakfast. My new day has begin. The results would come out today. My classmates all felt very nervous, so did I. Then one of my classmates called me, and invited me to play basketball in the afternoon. I like playing basketball, though I'm really poor at playing it. I and my parent visited redstart farm last Saturday,there're environment is so good.we're scavenge the hourse,The horse was leaded into the stable and each was put in a stall.Cows and sheep depends forage to feed.this so lifelikeness,we're got a lot of enjoyment from my job. in the end.owner preparative feasted on me.

日記記的是當天已經發生的事，用一般過去時。

大部分是用一般過去時，但是如果你寫的是你最近的近況，或者是習慣性動作就用一般現在時，其實一篇日記里可以用上各種時態的。
January 13 2005
It was the first day of our winter holiday. All of us were very happy. Why? Because we have one months to do things we love to do. We are free. Although we have some homework. But we can finish them in several days. And the rest time we can make good use of. My god! We have been very tired after hard studying. In winter holidays, I want to have full sleep and eat good food in order to replenish myself. Last but not the least, I will have a good rest.

既然是摘要,那就是對已近發生的事做概括,所以主體最通常的時態是一般過去時.一般現在時 ，但如果是科技實驗論文、產品說明摘要，一般只用一般現在時。