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   4641篇
  免费   881篇
  国内免费   1813篇
化学   1640篇
晶体学   48篇
力学   111篇
综合类   170篇
数学   1049篇
物理学   2317篇
无线电   2000篇
  2024年   43篇
  2023年   123篇
  2022年   155篇
  2021年   166篇
  2020年   139篇
  2019年   166篇
  2018年   111篇
  2017年   191篇
  2016年   193篇
  2015年   188篇
  2014年   350篇
  2013年   284篇
  2012年   302篇
  2011年   344篇
  2010年   314篇
  2009年   382篇
  2008年   378篇
  2007年   334篇
  2006年   324篇
  2005年   328篇
  2004年   278篇
  2003年   264篇
  2002年   217篇
  2001年   213篇
  2000年   159篇
  1999年   136篇
  1998年   138篇
  1997年   131篇
  1996年   167篇
  1995年   125篇
  1994年   163篇
  1993年   111篇
  1992年   112篇
  1991年   109篇
  1990年   86篇
  1989年   74篇
  1988年   13篇
  1987年   8篇
  1986年   6篇
  1985年   5篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
排序方式: 共有7335条查询结果,搜索用时 15 毫秒
891.
Production and properties of φ-meson under the extreme hot dense matter which is formed in Au + Au collisions at RHIC energy have been briefly reviewed.The issues are focused on transverse momentum (p T ) spectra of φ,elliptic flow of φ,nuclear modification factor of φ,the ratio of Ω(p T )/φ(p T ) versus p T,the ratio of Ω(p T /3)/φ(p T /2) versus p T /n q,spin alignment of φ and the enhancement of φ etc.These observables give the significant information of the strange quark dynamics in hot dense matter under the extreme condition.  相似文献   
892.
The cross sections of the fragments produced in the projectile fragmentation reactions of the even calcium isotopes from A=36 to A=52 are calculated using the statistical abrasion ablation model.The neutron skin thickness are studied by investigating the fragments isotopic cross section distributions.The neutron-skin thicknesses of the calcium isotopes have a good linear correlation to the peak positions of their fragment isotopic cross section distributions.The correlation between the neutron skin thickness and the neutron density distributions of 48 Ca is investigated by introducing a parameter to adjust the diffuseness parameter in the fermi-type density distribution.  相似文献   
893.
李宁  姚海波  陈曦  吴式枢 《中国物理 C》2010,34(12):1830-1835
By using the rigorous spectral representation of relativistic random phase approximation, the low-lying excitation of finite nuclei and its longitudinal response function for quasielastic electron scattering are calculated in the σ-ω model of quantum hadrodynamics. It is shown that the reproduction of the correct order of the 1- and 3- excitation states of 16O is due to the contribution of the exchange vertex. There is no significant influence of the retardation effect on the low-lying excitation states. In contrast, the retardation effect plays an important role in the electron scattering process of nuclei. The theoretical longitudinal responses of 12C and 40Ca, including the contributions of the exchange vertex and the retardation effect, are suppressed and reproduce the experimental data better than the results excluding them.  相似文献   
894.
By introducing internal degree, the deformation of hexagonal noncentrosymmetric crystal sheet can be described by the revised Cauchy-Born rule based on atomic potential. The instability criterion is deduced to investigate the inhomogeneous dislocation nucleation behavior of the crystal sheet under simple loading. The anisotropic characters of dislocation nucleation under uniaxial tension are studied by using the continuum method associated with the instability criterion. The results show a strong relationship between yield stress and crystal sheet chirality. The results also indicate that the instability criterion has sufficient ability to capture the dislocation nucleation site and expansion. To observe the internal dislocation phenomenon, the prediction of the dislocation nucleation site and expansion domain is illustrated by MD simulations. The developed method is another way to explain the dislocation nucleation phenomenon.  相似文献   
895.
Lifetimes of high spin states in 129Cs axe measured using the Doppler shift attenuation method. The high spin states of 129 Cs axe populated following the fusion evaporation reaction 124 Sn(UB, 6n)129 Cs at a beam energy of 65 MeV. The reduced transition probabilities B(E2) and the transition quadrupole moments Qt in the negativeand positive-paxity bands are deduced. The experimental results indicate that the Qt values of the negative parity band are smaller than those of the positive parity bands, probably due to different γ-deformation driving effects of different proton orbitals. The Qt values exhibit a considerable increase near the band crossing region in these bands. This behavior demonstrates that nuclear shape changing results from the neutron or proton alignments. The signature splitting of the πh11/2 and πg7/2 bands shows the opposite changing trend after backbending due to the h11~2 neutron and h11/2 proton alignments, respectively.  相似文献   
896.
We reinvestigate the collective effects of the retardation as well as the bending on the Coulomb excitation cross sections and also on the B(E2) strengths of some neutron-rich isotopes using the intermediate energy Coulomb excitation theory. It is found that the B(E2) strengths extracted from the experimental Coulomb excitation cross section data get suppressed approximately by 6%. Furthermore, the obtained B(E2) strengths in the energy range 30-100 MeV/A are found to be in better agreement with the corresponding values known from other sources, than those obtained by using the recoil-corrected relativistic Coulomb excitation theory.  相似文献   
897.
针对目前支持向量机多类分类方法存在的缺点,丈中对支持向量机的高斯函数进行改进,并提出一种结合留一法和单一验证法的参数选择新方案.基于3种雷达目标的HRRP数据,设计了相应的预处理算法,利用改进的SVM分类法用于高分辨距离像的雷达目标识别.从实验目标姿态稳定性、训练集大小稳定性和抗噪能力三个方面验证改进SVM的稳健性.  相似文献   
898.
什么是SOC?     
《电子质量》2009,(3):30-30
SoC(System on a Chip)中文名是才。20世纪90年代中期,因使用ASIC实现芯片组受到启发,萌生应该将完整计算机所有不同的功能块一次直接集成于一颗硅片上的想法。SoC应由可设计重用的IP组成,IP是具有复杂系统功能的能够独立出售的VLSI块;IP应采用深亚微米以上工艺技术;SoC中可以有多个MPU、DSP、MCU或其复合的IP。  相似文献   
899.
随着电路复杂性的增加,越来越多的设计者开始采用拥有知识产权的、设计良好的功能模块来加快系统开发.因此,需要相应的技术手段保护这些功能模块不被非法复制、篡改或窃取.针对FPGA开发中的知识产权保护问题,提出一种结合EDA软件和FPGA的IP(Intellectual Proterty)保护方法,有效的防止IP被窃取,以及防止最终在FPGA上实现设计的非法复制.  相似文献   
900.
关联分析和分类分析是数据挖掘的关键技术,但传统算法对入侵检测数据进行处理时有很多的不足,使用加权关联分析和机器分类算法构造混合型入侵检测系统,设计后的系统框架分为检测客户端和检测服务端,检测客户端主要是对数据的预处理和生成检测模型;检测服务端主要是判断检测模型,进行入侵数据的二次挖掘.结果说明,该系统具有良好的入侵数据分类效果.  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