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   111985篇
  免费   5896篇
  国内免费   3974篇
化学   48295篇
晶体学   1113篇
力学   8726篇
综合类   244篇
数学   35827篇
物理学   27650篇
  2023年   739篇
  2022年   718篇
  2021年   1178篇
  2020年   1428篇
  2019年   1297篇
  2018年   11268篇
  2017年   11026篇
  2016年   7482篇
  2015年   2372篇
  2014年   2221篇
  2013年   2806篇
  2012年   6893篇
  2011年   13428篇
  2010年   7670篇
  2009年   7957篇
  2008年   8672篇
  2007年   10572篇
  2006年   2043篇
  2005年   2809篇
  2004年   2784篇
  2003年   2918篇
  2002年   1882篇
  2001年   975篇
  2000年   975篇
  1999年   978篇
  1998年   852篇
  1997年   757篇
  1996年   874篇
  1995年   708篇
  1994年   620篇
  1993年   559篇
  1992年   496篇
  1991年   423篇
  1990年   372篇
  1989年   295篇
  1988年   274篇
  1987年   255篇
  1986年   196篇
  1985年   201篇
  1984年   176篇
  1983年   152篇
  1982年   121篇
  1981年   97篇
  1980年   95篇
  1979年   76篇
  1978年   60篇
  1976年   43篇
  1975年   47篇
  1973年   42篇
  1914年   45篇
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
41.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  相似文献   
42.
Ni–Co alloys have a wide range of applications in various fields owning to their excellent physical, chemical, and mechanical properties. In this paper, we prepare Ni–Co alloy coatings on 316L stain steel surfaces by electroplating. We present a novel approach utilizing a nanosecond laser to induce microtextures on Ni–Co alloy coatings. We study experimentally the effects of laser power and scanning rate on the surface morphologies of Ni–Co alloy coatings. The results indicate that the shape and size of induced microtextures can be controlled by the laser power and scanning rate. The size of grains increases with increase in the work current of the laser (WCL) at a certain scanning rate. With the WCL constant, the size of grains decreases with increase in scanning rate while their average height increases. It is a simple and easily-controlled method for the fabrication of microstructures on Ni–Co alloy coatings, which has promising applications in investigations of the properties of microtextured surfaces, such as friction, adhesion, and wetting.  相似文献   
43.
Journal of Thermal Analysis and Calorimetry - A phosphazene-based flame retardant (PBFA) was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine. To improve the flame retardancy...  相似文献   
44.
As a large group of cells in a central nervous system, astrocytes have a great influence on ion and energy metabolism in a nervous system. Disorders of neuronal ion and energy metabolism caused by impaired astrocytes play a key role in the pathogenesis of epilepsy. This paper reviews the existing computational models of epileptogenesis resulting from impaired astrocytes and presents several open perspectives with regard to ion and energy metabolism-induced epileptogenesis in a neuron-astrocyte-capillary coupled model.  相似文献   
45.
46.
47.
48.
The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr2·6H2O formed. In addition to this double salt, the three single salts LiBr·2H2O, KBr and MgBr2·6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer's electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones.  相似文献   
49.
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form.  相似文献   
50.
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