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   580498篇
  免费   7203篇
  国内免费   1632篇
化学   314191篇
晶体学   9031篇
力学   25054篇
综合类   22篇
数学   66329篇
物理学   174706篇
  2021年   4731篇
  2020年   5379篇
  2019年   5852篇
  2018年   7340篇
  2017年   7331篇
  2016年   11252篇
  2015年   7052篇
  2014年   11034篇
  2013年   26905篇
  2012年   20211篇
  2011年   24884篇
  2010年   17499篇
  2009年   17288篇
  2008年   22596篇
  2007年   22378篇
  2006年   20832篇
  2005年   18686篇
  2004年   17257篇
  2003年   15373篇
  2002年   15086篇
  2001年   17235篇
  2000年   13084篇
  1999年   10300篇
  1998年   8451篇
  1997年   8238篇
  1996年   7941篇
  1995年   7186篇
  1994年   7057篇
  1993年   6714篇
  1992年   7784篇
  1991年   7815篇
  1990年   7475篇
  1989年   7319篇
  1988年   7424篇
  1987年   7276篇
  1986年   6879篇
  1985年   8990篇
  1984年   9129篇
  1983年   7291篇
  1982年   7443篇
  1981年   7455篇
  1980年   6879篇
  1979年   7516篇
  1978年   7695篇
  1977年   7672篇
  1976年   7466篇
  1975年   6857篇
  1974年   6803篇
  1973年   6777篇
  1972年   4779篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
Molecular dynamics simulation was performed to study the formation of cluster structure, interfaces, and surfaces with different curvature radii in a perfect nanocrystal passed through by a nonlinear wave. It is shown that this process is a type of nanostructure self-organization in response to an external energy flux with subsequent development of a strong rotational field.  相似文献   
62.
63.
64.
Journal of Solid State Electrochemistry - Due to their distinctive chemical, electronic, and environmental properties, polypyrrole is used as a blocking barrier for methanol leakage in direct...  相似文献   
65.
Bruzy  N.  Coret  M.  Huneau  B.  Kermouche  G.  Mondon  M.  Bertrand  E.  Stainier  L. 《Experimental Mechanics》2019,59(8):1145-1157

The allotropic phase change from ferrite to austenite represents a moment of massive interplay between the microstructural and mechanical states of iron. The difference of compacity between the two phases induces a microplastic accommodation in the material at grain scale. However, mechanical heterogeneities resulting from the transformation process remain challenging to characterise due to the high temperature conditions it is associated with. We developed experimental equipment for in situ observation of α ? γ and γ ? α transformations. Images of the surface of an iron sample taken by an optical camera were used as input for a Digital Image Correlation (DIC) routine. Special care was taken to maximize image resolution to capture sub-grain phenomena. Observations show that, at the mesoscopic scale, shear strain fields exhibit strong localisations that are evidence of transformations that are occurring.

  相似文献   
66.
Russian Journal of Organic Chemistry - Methyl (Z)-3-[(2R,3R,4S,5S)-5-(2-methoxy-2-oxoethyl)-3,4-(isopropylidenedioxy)tetrahydrofuran-2-yl]-prop-2-enoate was synthesized, and its intramolecular...  相似文献   
67.
Numerous biological processes are connected with the efficient electron transfer reactions in proteins and peptides. In this review, we discuss briefly the relevance and current challenges associated with the voltammetric analysis of peptides and proteins with and without a metal redox center. Special attention is paid to the integration of electrochemical methods with new nanomaterials which offers amplification of multiplexing capabilities for simultaneous and very sensitive examination of various proteins. After critically discussing the most interesting approaches in the proteins/peptides voltammetric analysis reported so far, for the single or multiplexed examination of such biomolecules with demonstrated applicability in the real-sample analysis, existing challenges still need to be addressed and future directions in this field will be pointed out.  相似文献   
68.
Russian Journal of Organic Chemistry - The reaction of selenium dichloride with methyl and ethyl propiolates leads to formation of anti-Markovnikov adducts. The regio- and stereoselective synthesis...  相似文献   
69.
Journal of Thermal Analysis and Calorimetry - Low thermal conductivity is a primary issue in the development of efficient heat transfer fluids and materials required for the thermal management of...  相似文献   
70.
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded.  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