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   6847篇
  免费   822篇
  国内免费   796篇
化学   4935篇
晶体学   115篇
力学   381篇
综合类   35篇
数学   753篇
物理学   2246篇
  2024年   83篇
  2023年   139篇
  2022年   233篇
  2021年   278篇
  2020年   358篇
  2019年   350篇
  2018年   243篇
  2017年   219篇
  2016年   353篇
  2015年   359篇
  2014年   394篇
  2013年   515篇
  2012年   546篇
  2011年   580篇
  2010年   410篇
  2009年   371篇
  2008年   380篇
  2007年   313篇
  2006年   325篇
  2005年   243篇
  2004年   247篇
  2003年   185篇
  2002年   230篇
  2001年   170篇
  2000年   121篇
  1999年   117篇
  1998年   75篇
  1997年   70篇
  1996年   53篇
  1995年   42篇
  1994年   52篇
  1993年   38篇
  1992年   33篇
  1991年   41篇
  1990年   36篇
  1989年   29篇
  1988年   34篇
  1987年   16篇
  1986年   16篇
  1985年   20篇
  1984年   13篇
  1983年   12篇
  1982年   11篇
  1981年   7篇
  1979年   6篇
  1978年   8篇
  1977年   7篇
  1976年   7篇
  1975年   8篇
  1974年   6篇
排序方式: 共有8465条查询结果,搜索用时 15 毫秒
31.
32.
We investigate the multipartite entanglement in arbitrary dimensional systems, and separability criteria for nonseparability in n-partite quantum states are derived. Examples such as the generalized noisy-W state and the GHZ basis states mixed with white noise are provided to show that our criteria are independent of and stronger than previously reported ones. Our criteria can also be expressed by the elements of the density matrix, which allows a simple and practical evaluation and computation. The experimental implementation of our criteria is also discussed.  相似文献   
33.
The quantum theory of a forward Stokes generation by means of stimulated Raman scattering is considered in the case of a pre-gaussian pump composed by two and three telegraphs. As for the case of a colored chaotic pump the mean Stokes intensity is found to be enhanced over that resulting from a coherent pump in both transient and steady-state limits. In the limit that the pre-gaussian bandwidth becomes large, the mean Stokes intensity also becomes identical with that resulting from a coherent pump.  相似文献   
34.
During the last 20 years, beamline BL08B has been upgraded step by step from a photon beam‐position monitor (BPM) to a testing beamline and a single‐grating beamline that enables experiments to record X‐ray photo‐emission spectra (XPS) and X‐ray absorption spectra (XAS) for research in solar physics, organic semiconductor materials and spinel oxides, with soft X‐ray photon energies in the range 300–1000 eV. Demands for photon energy to extend to the extreme ultraviolet region for applications in nano‐fabrication and topological thin films are increasing. The basic spherical‐grating monochromator beamline was again upgraded by adding a second grating that delivers photons of energy from 80 to 420 eV. Four end‐stations were designed for experiments with XPS, XAS, interstellar photoprocess systems (IPS) and extreme‐ultraviolet lithography (EUVL) in the scheduled beam time. The data from these experiments show a large count rate in core levels probed and excellent statistics on background normalization in the L‐edge adsorption spectrum.  相似文献   
35.
In this article, non-smooth dynamics of an elastic structure excited by a harmonic impactor motion is studied through a combination of experimental, numerical, and analytical efforts. The test apparatus consists of a stainless steel cantilever structure with a tip mass that is impacted by a shaker. Soft impact between the impactor and the structure is considered, and bifurcations with respect to quasi-static variation of the shaker excitation frequency are examined. In the experiments, qualitative changes that can be associated with grazing and corner-collision bifurcations are observed. Aperiodic motions are also observed in the vicinity of the non-smooth bifurcation points. Assuming the system response to be dominated by the structure’s fundamental mode, a non-autonomous, single degree-of-freedom model is developed and used for local analysis and numerical simulations. The predicted grazing and corner-collision bifurcations are in agreement with the experimental results. To study the local bifurcation behavior at the corner-collision point and explore the mechanism responsible for the aperiodic motions, a derivation is carried out to construct local Poincaré maps of periodic orbits at a corner-collision point such as the one observed in the soft-impact oscillator.  相似文献   
36.
37.
孔令华  曹莹  王兰  万隆 《计算物理》2011,28(5):730-736
对一类带三次非线性项的四阶Schr(o)dinger方程提出分裂多辛格式.其基本思想是将多辛算法和分裂方法相结合,既具有多辛格式固有的保多辛几何结构的特性,又发挥了分裂方法在计算上灵活高效的特点.数值实验结果表明,分裂多辛格式比其它传统的多辛格式更节约计算时间和计算机的内存,从而更加优越.  相似文献   
38.
In this article, we propose a three-party quantum secret sharing protocol with four-state Grover algorithm. The protocol has several advantages. It uses only four initial states which simplifies its experimental implementation. It has a higher encoding capacity, each two-qubit state provides two bits of information. We have experimentally demonstrated the protocol in a nuclear magnetic resonance quantum information processor successfully.  相似文献   
39.
Neural Network Models for Finline Discontinuities   总被引:1,自引:0,他引:1  
The radial basis network is used as the finline discontinuities electromagnetic artifical neural network(EMANN) models. EM software analysis is employed to characterize finline discontinuities. EMANN models are then trained using physical parameters and frequency as inputs and equivalent electric circuit element parameters of finline discontinuities as outputs. Once trained , the EMANN models can simulate equivalent electric circuit element parameters of finline step, notch and strip very fast and efficiently.  相似文献   
40.
比较了不同基体改进剂 ,不同涂层对镓在热解石墨管中原子化的影响。研究了以硝酸镍为基体改进剂 ,以涂钼热解石墨管为原子化器镓的原子化机理 ,优化了各项参数 ,找到了一种测定复杂样品中痕量镓的新方法。方法特征量为 2 1 2× 1 0 -1 1 g ,检出限为 1 4× 1 0 -1 0 g ,RSD≤ 3 6 % (n =1 1 ) ,样品回收率 97 4 %~1 0 2 7%。  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