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   332359篇
  免费   18827篇
  国内免费   12548篇
化学   187874篇
晶体学   5086篇
力学   16418篇
综合类   667篇
数学   38010篇
物理学   115679篇
  2022年   4686篇
  2021年   5111篇
  2020年   5857篇
  2019年   5878篇
  2018年   6256篇
  2017年   5837篇
  2016年   8712篇
  2015年   7024篇
  2014年   9692篇
  2013年   17507篇
  2012年   16444篇
  2011年   18649篇
  2010年   13175篇
  2009年   12872篇
  2008年   15270篇
  2007年   14568篇
  2006年   13725篇
  2005年   12055篇
  2004年   10469篇
  2003年   8964篇
  2002年   8658篇
  2001年   9221篇
  2000年   7247篇
  1999年   6253篇
  1998年   5258篇
  1997年   4996篇
  1996年   4830篇
  1995年   4362篇
  1994年   4174篇
  1993年   4016篇
  1992年   4032篇
  1991年   4087篇
  1990年   3715篇
  1989年   3516篇
  1988年   3434篇
  1987年   3284篇
  1986年   3127篇
  1985年   4061篇
  1984年   4190篇
  1983年   3347篇
  1982年   3530篇
  1981年   3411篇
  1980年   3286篇
  1979年   3357篇
  1978年   3443篇
  1977年   3365篇
  1976年   3463篇
  1975年   3161篇
  1974年   3153篇
  1973年   3207篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
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   
73.
Novel pyrene‐fused unsymmetrical phthalocyanine derivatives 2,3,9,10,16,17‐hexakis(2,6‐dimethylphenoxy)‐22,25‐diaza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc complex Zn[Pc(Pz‐pyrene)(OC8H9)6] ( 1 ) and 2,3,9,10‐tra(2,6‐dimethylphenoxy)‐15,18,22,25‐traza(2,7‐di‐tert‐butylpyrene)[4,5]phthalocyaninato zinc compound Zn[Pc(Pz‐pyrene)2(OC8H9)4] ( 2 ) were isolated for the first time. These unsymmetrical pyrene‐fused phthalocyanine derivatives have been characterized by a wide range of spectroscopic and electrochemical methods. In particular, the pyrene‐fused phthalocyanine structure was unambiguously revealed on the basis of single crystal X‐ray diffraction analysis of 1 , representing the first structurally characterized phthalocyanine derivative fused with an aromatic moiety larger than benzene.  相似文献   
74.
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   
75.
76.
77.
78.
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   
79.
80.
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