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   384150篇
  免费   3166篇
  国内免费   987篇
化学   162322篇
晶体学   5039篇
力学   16576篇
综合类   2篇
数学   50611篇
物理学   107322篇
无线电   46431篇
  2020年   2005篇
  2019年   2251篇
  2018年   11986篇
  2017年   12838篇
  2016年   8424篇
  2015年   3618篇
  2014年   4375篇
  2013年   12001篇
  2012年   12947篇
  2011年   23421篇
  2010年   14836篇
  2009年   15033篇
  2008年   21049篇
  2007年   25036篇
  2006年   10113篇
  2005年   16673篇
  2004年   12261篇
  2003年   11329篇
  2002年   9082篇
  2001年   8796篇
  2000年   7166篇
  1999年   5599篇
  1998年   4925篇
  1997年   4956篇
  1996年   4709篇
  1995年   4432篇
  1994年   4315篇
  1993年   4350篇
  1992年   4533篇
  1991年   4599篇
  1990年   4350篇
  1989年   4183篇
  1988年   4166篇
  1987年   3618篇
  1986年   3456篇
  1985年   4541篇
  1984年   4723篇
  1983年   3949篇
  1982年   4252篇
  1981年   4092篇
  1980年   3946篇
  1979年   3965篇
  1978年   4195篇
  1977年   3918篇
  1976年   4147篇
  1975年   3706篇
  1974年   3802篇
  1973年   4184篇
  1972年   2580篇
  1971年   2019篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
33.
We summarize the results of our recent work on Bäcklund transformations (BTs), particularly focusing on the relation between BTs and infinitesimal symmetries. We present a BT for an associated Degasperis–Procesi (aDP) equation and its superposition principle and investigate the solutions generated by applying this BT. Following our general methodology, we use the superposition principle of the BT to generate the infinitesimal symmetries of the aDP equation.  相似文献   
34.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
35.
36.
37.
38.
39.
40.
A generic strategy based on the use of CdSe/ZnS Quantum Dots (QDs) as elemental labels for protein quantification, using immunoassays with elemental mass spectrometry (ICP-MS), detection is presented. In this strategy, streptavidin modified QDs (QDs-SA) are bioconjugated to a biotinylated secondary antibody (b-Ab2). After a multi-technique characterization of the synthesized generic platform (QDs-SA-b-Ab2) it was applied to the sequential quantification of five proteins (transferrin, complement C3, apolipoprotein A1, transthyretin and apolipoprotein A4) at different concentration levels in human serum samples. It is shown how this generic strategy does only require the appropriate unlabeled primary antibody for each protein to be detected. Therefore, it introduces a way out to the need for the cumbersome and specific bioconjugation of the QDs to the corresponding specific recognition antibody for every target analyte (protein). Results obtained were validated with those obtained using UV–vis spectrophotometry and commercial ELISA Kits.  相似文献   
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