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   266705篇
  免费   3449篇
  国内免费   808篇
化学   136575篇
晶体学   3887篇
力学   11499篇
综合类   1篇
数学   31698篇
物理学   87302篇
  2020年   2244篇
  2019年   2345篇
  2018年   3102篇
  2017年   3033篇
  2016年   4800篇
  2015年   3163篇
  2014年   4834篇
  2013年   11938篇
  2012年   8954篇
  2011年   11121篇
  2010年   7588篇
  2009年   7390篇
  2008年   10362篇
  2007年   10312篇
  2006年   9704篇
  2005年   8741篇
  2004年   7895篇
  2003年   6926篇
  2002年   6835篇
  2001年   7680篇
  2000年   5925篇
  1999年   4638篇
  1998年   3912篇
  1997年   3820篇
  1996年   3755篇
  1995年   3412篇
  1994年   3396篇
  1993年   3569篇
  1992年   3574篇
  1991年   3660篇
  1990年   3434篇
  1989年   3325篇
  1988年   3380篇
  1987年   3255篇
  1986年   3072篇
  1985年   4244篇
  1984年   4433篇
  1983年   3575篇
  1982年   3791篇
  1981年   3679篇
  1980年   3550篇
  1979年   3637篇
  1978年   3753篇
  1977年   3669篇
  1976年   3726篇
  1975年   3406篇
  1974年   3409篇
  1973年   3453篇
  1972年   2353篇
  1971年   1972篇
排序方式: 共有10000条查询结果,搜索用时 482 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.
34.
35.
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   
36.
37.
A new strategy for the synthesis of tetrahydroisoquinolines based on the Pd0‐catalyzed intramolecular α‐arylation of sulfones is reported. The combination of this Pd‐catalyzed reaction with intermolecular Michael and aza‐Michael reactions allows the development of two‐ and three‐step domino processes to synthesize diversely functionalized scaffolds from readily available starting materials.  相似文献   
38.
39.
This study was aimed at the development of a conductometric biosensor based on acetylcholinesterase considering the feasibility of its application for the inhibitory analysis of various toxicants. In this paper, the optimum conditions for enzyme immobilization on the transducer surface are selected as well as the optimum concentration of substrate for inhibitory analysis. Sensitivity of the developed biosensor to different classes of toxic compounds (organophosphorus pesticides, heavy metal ions, surfactants, aflatoxin, glycoalkaloids) was tested. It is shown that the developed biosensor can be successfully used for the analysis of pesticides and mycotoxins, as well as for determination of total toxicity of the samples. A new method of biosensor analysis of toxic substances of different classes in complex multicomponent aqueous samples is proposed.  相似文献   
40.
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