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   216883篇
  免费   3681篇
  国内免费   536篇
化学   118152篇
晶体学   3233篇
力学   8610篇
综合类   3篇
数学   26814篇
物理学   64288篇
  2021年   1696篇
  2020年   2045篇
  2019年   2149篇
  2018年   2924篇
  2017年   2839篇
  2016年   4619篇
  2015年   3216篇
  2014年   4467篇
  2013年   10421篇
  2012年   8941篇
  2011年   10220篇
  2010年   6983篇
  2009年   6610篇
  2008年   9363篇
  2007年   9270篇
  2006年   8584篇
  2005年   7939篇
  2004年   7145篇
  2003年   6241篇
  2002年   5905篇
  2001年   6038篇
  2000年   4572篇
  1999年   3449篇
  1998年   2873篇
  1997年   2741篇
  1996年   2685篇
  1995年   2400篇
  1994年   2428篇
  1993年   2356篇
  1992年   2661篇
  1991年   2537篇
  1990年   2482篇
  1989年   2401篇
  1988年   2364篇
  1987年   2366篇
  1986年   2230篇
  1985年   2979篇
  1984年   3004篇
  1983年   2619篇
  1982年   2797篇
  1981年   2598篇
  1980年   2543篇
  1979年   2672篇
  1978年   2688篇
  1977年   2578篇
  1976年   2679篇
  1975年   2572篇
  1974年   2535篇
  1973年   2698篇
  1972年   1698篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10−3 S cm−1 at 75 °C and 80 % relative humidity).  相似文献   
22.
23.
24.
The European Physical Journal Special Topics - The removal of suspended particles from the interior of a thermocapillary liquid bridge via a finite-particle-size effect restricting the particle...  相似文献   
25.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling.  相似文献   
26.
27.
28.
29.
In this paper, we present an approach of dynamic mesh adaptation for simulating complex 3‐dimensional incompressible moving‐boundary flows by immersed boundary methods. Tetrahedral meshes are adapted by a hierarchical refining/coarsening algorithm. Regular refinement is accomplished by dividing 1 tetrahedron into 8 subcells, and irregular refinement is only for eliminating the hanging points. Merging the 8 subcells obtained by regular refinement, the mesh is coarsened. With hierarchical refining/coarsening, mesh adaptivity can be achieved by adjusting the mesh only 1 time for each adaptation period. The level difference between 2 neighboring cells never exceeds 1, and the geometrical quality of mesh does not degrade as the level of adaptive mesh increases. A predictor‐corrector scheme is introduced to eliminate the phase lag between adapted mesh and unsteady solution. The error caused by each solution transferring from the old mesh to the new adapted one is small because most of the nodes on the 2 meshes are coincident. An immersed boundary method named local domain‐free discretization is employed to solve the flow equations. Several numerical experiments have been conducted for 3‐dimensional incompressible moving‐boundary flows. By using the present approach, the number of mesh nodes is reduced greatly while the accuracy of solution can be preserved.  相似文献   
30.
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation.  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