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   274591篇
  免费   2672篇
  国内免费   655篇
化学   147777篇
晶体学   4214篇
力学   12021篇
综合类   9篇
数学   30402篇
物理学   83495篇
  2020年   2283篇
  2019年   2499篇
  2018年   3305篇
  2017年   3264篇
  2016年   4774篇
  2015年   2872篇
  2014年   4579篇
  2013年   11145篇
  2012年   8563篇
  2011年   10451篇
  2010年   7462篇
  2009年   7162篇
  2008年   9762篇
  2007年   9937篇
  2006年   9274篇
  2005年   8370篇
  2004年   7680篇
  2003年   6929篇
  2002年   6834篇
  2001年   7419篇
  2000年   5725篇
  1999年   4404篇
  1998年   3911篇
  1997年   3886篇
  1996年   3636篇
  1995年   3370篇
  1994年   3523篇
  1993年   3222篇
  1992年   3695篇
  1991年   3701篇
  1990年   3622篇
  1989年   3488篇
  1988年   3588篇
  1987年   3485篇
  1986年   3313篇
  1985年   4403篇
  1984年   4657篇
  1983年   3889篇
  1982年   4035篇
  1981年   3953篇
  1980年   3933篇
  1979年   3887篇
  1978年   4194篇
  1977年   4117篇
  1976年   4182篇
  1975年   3850篇
  1974年   3900篇
  1973年   4054篇
  1972年   2855篇
  1971年   2381篇
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
101.
The present paper is a continuation of comprehensive study regarding to synthesis and properties of pyrazoles and their derivatives. In its framework an experimental and theoretical studies of thermal decomposition of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline were performed. It was found, that the decompositions of the mentioned pyrazoline system in the solution and at the melted state proceed via completely different molecular mechanisms. These mechanisms have been explained in the framework of the Molecular Electron Density Theory (MEDT) with the computational level of B3LYP/6-31G(d). A Bonding Evolution Theory (BET) examination of dehydrochlorination of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline permits elucidation of the molecular mechanism. It was found, that on the contrary for most known HCl extrusion processes in solution, this reaction is realised via single-step mechanism.  相似文献   
102.
Russian Chemical Bulletin - Gradient polymer composites were prepared by melt-mixing of carbon black and polypropylene in a compounder and subsequent hot pressing of pellets. The thermally treated...  相似文献   
103.
Journal of Structural Chemistry - Thermodynamic characteristics are calculated for aqueous alkanolamine solutions that are obtained by substituting alkyl radicals for the protons in the amino group...  相似文献   
104.
Li  C.  Zhang  D.  Cheng  G.  Zhu  Y. 《Experimental Mechanics》2020,60(3):329-343
Experimental Mechanics - There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices....  相似文献   
105.
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments.  相似文献   
106.
107.
Radiophysics and Quantum Electronics - We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in...  相似文献   
108.
The aim of the study presented in this paper was to characterize quantitatively the erosion of aluminum cathodes in high-current vacuum arcs. The experimental setup comprised two current generators. The first one, capable of generating a current of amplitude up to 350 kA, was used to produce a plasma jet, that is, the object to be investigated. The second generator was used to produce a source of probe radiation for imaging the object under investigation in soft x rays of energy ?ν ≈ 0.5–3 keV. The findings of the study are based on experimental data obtained by electrophysical and radiographic methods. It has been shown that the cathode erosion rate in a high-current vacuum arc is a function of the charge passed through the cathode.  相似文献   
109.
Optics and Spectroscopy - The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical...  相似文献   
110.
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