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   7642篇
  免费   1279篇
  国内免费   1142篇
化学   6191篇
晶体学   105篇
力学   376篇
综合类   117篇
数学   866篇
物理学   2408篇
  2024年   37篇
  2023年   154篇
  2022年   277篇
  2021年   330篇
  2020年   360篇
  2019年   358篇
  2018年   328篇
  2017年   288篇
  2016年   378篇
  2015年   419篇
  2014年   475篇
  2013年   587篇
  2012年   660篇
  2011年   689篇
  2010年   531篇
  2009年   483篇
  2008年   531篇
  2007年   415篇
  2006年   367篇
  2005年   320篇
  2004年   250篇
  2003年   238篇
  2002年   274篇
  2001年   222篇
  2000年   159篇
  1999年   132篇
  1998年   96篇
  1997年   62篇
  1996年   102篇
  1995年   87篇
  1994年   61篇
  1993年   49篇
  1992年   45篇
  1991年   34篇
  1990年   43篇
  1989年   25篇
  1988年   23篇
  1987年   24篇
  1986年   12篇
  1985年   23篇
  1984年   6篇
  1983年   9篇
  1982年   10篇
  1981年   6篇
  1979年   7篇
  1977年   6篇
  1975年   9篇
  1974年   9篇
  1972年   11篇
  1971年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The heavy fermion system exhibits properties that range from an incommensurate antiferromagnet for small to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of and a new, commensurate antiferromagnetism that orders separately. The coexistence of -electron superconductivity with two distinct -electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors.  相似文献   
42.
The decay rate gamma of an excited dipole molecule inside a waveguide is evaluated for the strongly coupled matter-field case near a cutoff frequency omegac without using perturbation analysis. Because of the singularity in the density of photon states at the cutoff frequency, we find that gamma depends nonanalytically on the coupling constant g as g4/3, which leads to a vast increase in the decay rate.  相似文献   
43.
Wan Y  Afshar S  Zou L  Chen L  Bao X 《Optics letters》2005,30(10):1099-1101
Subpeaks in the Brillouin loss spectra of distributed fiber-optic sensors were observed for what is believed to be the first time and studied. We discovered that the Fourier spectrum of the pulsed signal and the off-resonance oscillation both contributed to subpeaks. The off-resonance oscillation at frequency /v - vB/ is the oscillation in the Brillouin time domain when beat frequency v of the two counterpropagating laser beams does not match local Brillouin frequency vB. This study is important in differentiating the subpeaks from actual strain-temperature peaks.  相似文献   
44.
Yu Q  Bao X  Ravet F  Chen L 《Optics letters》2005,30(17):2215-2217
The second-order partial derivative of the Stokes signal with respect to frequency and position shows a maximum or minimum at the boundary between two different strained sections. This idea is used to locate the boundary of different stress regions. Knowing the boundaries, we then fit the Brillouin spectrum at the middle between them to get the strain value. This allows a location accuracy of between 5 and 10 cm, which is shorter than the pulse length of 20 cm used in the experiment. The lowest detectable Brillouin frequency difference between two strain sections is 1.2 MHz.  相似文献   
45.
Based on the concept of adiabatic invariant, the perturbation to Meisymmetry and adiabatic invariants for nonholonomic mechanical systems interms of quasi-coordinates are studied. The definition of the perturbationto Mei symmetry for the system is presented, and the criterion of theperturbation to Mei symmetry is given. Meanwhile, the Mei adiabaticinvariants for the perturbed system are obtained.  相似文献   
46.
Fast evolving nanoseienees and nanotechnology in China has made it one of the front countries of nanotechnology development. Ill this review, we summarize some most recent progresses in nanoseienee research and nanotechnology development in China. The topics we selected in this article include llano-fabrication, nanocatalysis, bioinspired nanoteehnology, green printing nanotechnology, nanoplasmonics, nanomedicine, nanomaterials and their applications, energy and environmental nanoteehnology, nano EHS (nanosafety), etc. Most of them have great potentials in applications or application-related key issues in future.  相似文献   
47.
以菲涅耳-基尔霍夫衍射理论为基础,对通过非线性介质的高斯光束传输行为进行理论分析,分别给出了强吸收、无吸收情况下开孔、闭孔Z扫描曲线公式;对不同条件下非线性介质的归一化透过率进行数值模拟计算,发现Z扫描曲线透射峰和透射谷表现出3种新的特性:随着入射激光峰值光强的增加,Z扫描曲线透射峰的高度受到抑制,而透射谷则加强变得更深;非线性相移的增加对Z扫描曲线透射峰和透射谷均有增高和加深的作用;激光束束腰半径越大,Z扫描曲线的峰谷特征越明显。  相似文献   
48.
包伯成  康祝圣  许建平  胡文 《物理学报》2009,58(3):1420-1431
由平方映射延伸构造出了一类含指数项的广义平方映射,并由一维映射通过一次耦合项得到了二维映射.利用一参数分岔图、二参数动力学行为分布图、映射迭代曲线和吸引子相图等方法对这类广义平方映射进行了分析和仿真.研究结果表明:一维广义平方映射分布在一个单位区域内的,有着与单峰平方映射相类似的非线性动力学现象;而二维广义平方映射则存在Hopf分岔和锁频等现象,有着复杂多变、形状奇异的极限环和混沌吸引子. 关键词: 广义平方映射 分岔 迭代曲线 吸引子  相似文献   
49.
Ming Zeng  Youfu Li  Qinghao Meng  Ting Yang  Jian Liu 《Optik》2012,123(6):511-520
Many applications of histogram-based techniques for the purposes of image enhancement are well known. However, these techniques often fail to produce satisfactory results for a broad variety of low-contrast images (e.g., X-ray images). In this paper, we propose a new form of histogram for image contrast enhancement. The input image is first divided into several equal-sized regions according to the intensities of gradients, their corresponding statistical values of gray levels are then modified respectively, and finally the processed histogram for the whole image is obtained by the summation of all the weighted values of regions. The fundamental characteristic of this new form of histogram is that the amplitudes of its components can objectively reflect the contribution of the gray levels to the representation of image information. Accordingly, this new histogram is called gray-level information histogram. The performance of many histogram-based enhancement techniques might be improved dramatically using the proposed histogram. Testing on the X-ray images validates the effectiveness of the new histogram.  相似文献   
50.
包伯成  刘中  许建平 《中国物理 B》2010,19(3):30510-030510
This paper presents a new smooth memristor oscillator, which is derived from Chua's oscillator by replacing Chua's diode with a flux-controlled memristor and a negative conductance. Novel parameters and initial conditions are dependent upon dynamical behaviours such as transient chaos and stable chaos with an intermittence period and are found in the smooth memristor oscillator. By using dynamical analysis approaches including time series, phase portraits and bifurcation diagrams, the dynamical behaviours of the proposed memristor oscillator are effectively investigated in this paper.  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