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   714185篇
  免费   7902篇
  国内免费   2006篇
化学   359159篇
晶体学   10681篇
力学   34759篇
综合类   20篇
数学   98502篇
物理学   220972篇
  2021年   5786篇
  2020年   6339篇
  2019年   6934篇
  2018年   13835篇
  2017年   14208篇
  2016年   15759篇
  2015年   8757篇
  2014年   13193篇
  2013年   31161篇
  2012年   26147篇
  2011年   35862篇
  2010年   24981篇
  2009年   24826篇
  2008年   32485篇
  2007年   34239篇
  2006年   24354篇
  2005年   25182篇
  2004年   21902篇
  2003年   19631篇
  2002年   18526篇
  2001年   20078篇
  2000年   15344篇
  1999年   11935篇
  1998年   9977篇
  1997年   9621篇
  1996年   9297篇
  1995年   8169篇
  1994年   8151篇
  1993年   7853篇
  1992年   8633篇
  1991年   8876篇
  1990年   8493篇
  1989年   8252篇
  1988年   8105篇
  1987年   8074篇
  1986年   7642篇
  1985年   9857篇
  1984年   10062篇
  1983年   8163篇
  1982年   8320篇
  1981年   8081篇
  1980年   7664篇
  1979年   8298篇
  1978年   8420篇
  1977年   8245篇
  1976年   8202篇
  1975年   7707篇
  1974年   7611篇
  1973年   7614篇
  1972年   5407篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
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   
102.
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   
103.
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   
104.

A procedure was suggested for preparing brominated polyols of reduced viscosity for the synthesis of foamed polyurethanes of reduced flammability. The flame-retarding action of the synthesized polyol tetrabromophthalate in polyurethane was studied in comparison with that of other widely used flame retardants. Evaluation of the effect exerted on the flammability of the polurethane compound by the polyol tetrabromophthalate synthesized, melamine, and aluminum hydroxide shows that all the samples containing flame retardants are self-extinguishing. The shortest combustion time was observed for the sample containing 6% polyol tetrabromophthalate synthesized. The sample containing as a flame retardant additive solely the synthesized polyole tetrabromophthalate also exhibits the highest performance as a heat-insulating material from the viewpoint of thermal conductivity.

  相似文献   
105.
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   
106.

A model with 16 moments is here presented in the framework of RET of polyatomic gases. It furnishes as principal subsystem the relativistic counterpart of a work by Arima T., Ruggeri T., Sugiyama M.; this is present in literature and treats the non relativistic case which incorporates relaxation processes of molecular rotation and vibration. Another principal subsystem is the natural extension of the 14 moments model by Pennisi S. and Ruggeri T.; this is also present in literature in the relativistic framework but where the trace of the third balance equation is neglected. Its extension is found here for the case when this trace isn’t neglected.

  相似文献   
107.
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   
108.
Russian Journal of Applied Chemistry - Quenching method was used to obtain glasses in the system xWO3-(100-x)P2O5 (x = 70, 75, 80, 82 mol %). The electrical conductivity of the compositions was...  相似文献   
109.
Doklady Mathematics - An Erratum to this paper has been published: https://doi.org/10.1134/S1064562421330012  相似文献   
110.
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