首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   82747篇
  免费   6731篇
  国内免费   6296篇
  2024年   37篇
  2023年   966篇
  2022年   1184篇
  2021年   3961篇
  2020年   2891篇
  2019年   3590篇
  2018年   3504篇
  2017年   2554篇
  2016年   3592篇
  2015年   5310篇
  2014年   6190篇
  2013年   6586篇
  2012年   7860篇
  2011年   6932篇
  2010年   4248篇
  2009年   3826篇
  2008年   4356篇
  2007年   3937篇
  2006年   3469篇
  2005年   2885篇
  2004年   2383篇
  2003年   2098篇
  2002年   1754篇
  2001年   1445篇
  2000年   1398篇
  1999年   1315篇
  1998年   765篇
  1997年   740篇
  1996年   746篇
  1995年   683篇
  1994年   601篇
  1993年   421篇
  1992年   610篇
  1991年   468篇
  1990年   426篇
  1989年   314篇
  1988年   257篇
  1987年   245篇
  1986年   175篇
  1985年   207篇
  1984年   119篇
  1983年   125篇
  1982年   75篇
  1981年   61篇
  1980年   41篇
  1979年   64篇
  1978年   32篇
  1977年   31篇
  1974年   40篇
  1973年   34篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
1.
2.
3.
4.
5.
6.
An experiment was conducted to investigate the effect of phytase transgenic corn (PTC) on intestinal microflora, and the fate of transgenic DNA and protein in the digesta and tissues of broilers. A total of 160 1-day-old Arbor Acres commercial male broilers were randomly assigned to 20 cages (8 chicks per cage) with 10 cages (replicates) for each treatment. Birds were fed with a diet containing either PTC (54.0% during 1–21 days and 61.0% during 22–42 days) or non-transgenic isogenic control corn (CC) for a duration of 42 days. There were no significant differences (P>0.05) between birds fed with the PTC diets and those fed with the CC diets in the quantities of aerobic bacteria, anaerobic bacteria, colibacillus and lactobacilli, or microbial diversities in the contents of ileum and cecum. Transgenic phyA2 DNA was not detected, but phyA2 protein was detected in the digesta of duodenum and jejunum of broilers fed with the PTC diets. Both transgenic phyA2 DNA and protein fragments were not found in the digesta of the ileum and rectum, heart, liver, kidney, and breast or thigh muscles of broilers fed with the PTC diets. It was concluded that PTC had no adverse effect on the quantity and diversity of gut microorganisms; Transgenic phyA2 DNA or protein was rapidly degraded in the intestinal tract and was not transferred to the tissues of broilers.  相似文献   
7.
8.
A recursive least squares based on Multi-model is proposed for non-uniformly sampled-data nonlinear (NUSDN) systems. The corresponding state space model of an NUSDN system is derived using lifting technique. Taking advantage of the Fuzzy c-Mean Clustering algorithm, NUSDN is divided into several local models. The basic idea is that the NUSDN system is viewed as a model switching system under a given rule. Once the local models are identified, the global model is determined. A pH neutralization process validate the performance of the proposed algorithm.  相似文献   
9.
A circular slit-groove surface plasmon polaritons (SPPs) launcher surrounding a photodetector is employed theoretically to enhance the photocurrent of atypical Si-Ge photodetectors. The slit and grooves are designed such that the SPPs are focused at the center of the absorption layer of the photodetector to result in additional electric current. Fabry–Perot resonance condition accurately calculates the period of the groove, slit-groove distance, photodetector radius, and slit-photodetector distance. The manipulation leads to constructive interference between the incident light impinging from the top and the SPPs propagating toward the photodetector. Simulation result shows that photocurrent increases by approximately 13-fold when the SPPs are introduced.  相似文献   
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号