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   23760篇
  免费   3959篇
  国内免费   3242篇
化学   17359篇
晶体学   256篇
力学   1263篇
综合类   249篇
数学   2923篇
物理学   8911篇
  2024年   41篇
  2023年   482篇
  2022年   739篇
  2021年   852篇
  2020年   994篇
  2019年   1060篇
  2018年   813篇
  2017年   796篇
  2016年   1116篇
  2015年   1152篇
  2014年   1410篇
  2013年   1730篇
  2012年   2146篇
  2011年   2170篇
  2010年   1492篇
  2009年   1465篇
  2008年   1627篇
  2007年   1448篇
  2006年   1279篇
  2005年   1088篇
  2004年   845篇
  2003年   684篇
  2002年   743篇
  2001年   593篇
  2000年   535篇
  1999年   513篇
  1998年   429篇
  1997年   373篇
  1996年   369篇
  1995年   323篇
  1994年   257篇
  1993年   254篇
  1992年   182篇
  1991年   160篇
  1990年   147篇
  1989年   121篇
  1988年   107篇
  1987年   73篇
  1986年   65篇
  1985年   81篇
  1984年   42篇
  1983年   32篇
  1982年   39篇
  1981年   17篇
  1980年   10篇
  1979年   13篇
  1978年   8篇
  1977年   9篇
  1976年   10篇
  1972年   5篇
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
131.
In this paper, specific issues related to high-density perpendicular magnetic recording processes, such as transition noise properties and cross-track correlation lengths, were investigated with the help of micromagnetic analysis. The effects of media parameters were taken into consideration, including intergranular exchange coupling, and exchange distribution, irregular grain shapes, magnetization saturation distribution, and anisotropy distribution. The micromagnetic simulation results showed that the effect of anisotropy distribution on transition noise is more significant than magnetization saturation distribution, and it is crucial to reduce this effect to achieve a high signal-to-noise ratio. Additionally, a new method to further estimate the partial erasure threshold was proposed to approximate the partial erasure effects, and the relation between the microtrack jitter and total track jitter was investigated.  相似文献   
132.
Instability of Solitary Waves in Nonlinear Composite Media   总被引:1,自引:0,他引:1  
In this paper,we investigate a class of Hamiltonian systems arising in nonlinear composite media.By detailed analysis and computation we obtain a decaying estimates on the semigroup and prove the orbitalinstability of two families of explicit solitary wave solutions (slow family in anisotropic case and solitary wavesin isotropic case),which theoretically verify the related guess and numerical results.  相似文献   
133.
The BCQ and the Abadie CQ for infinite systems of convex inequalities in Banach spaces are characterized in terms of the upper semi-continuity of the convex cones generated by the subdifferentials of active convex functions. Some relationships with other constraint qualifications such as the CPLV and the Slate condition are also studied. Applications in best approximation theory are provided.  相似文献   
134.
Introduction Parkinson′sdisease(PD),alsocalledshaking palsy,isaneurodegenerativedisorderandfrequently occursinthepeopleabovetheageof65[1].PDisa relativelycommonneurodegenerativedisorder,which hasclinicalsymptomsincludingbradykinesia,rest tremor,rigidity,…  相似文献   
135.
In this paper we investigate the acute triangulations of flat Mobius strips. We find out that we can always triangulate a flat Mobius strip with at most nine acute triangles, and sometimes (but not always) that many triangles are really needed.  相似文献   
136.
137.
900 MHz 1H NMR (nuclear magnetic resonance) spectroscopy was used to analyze metabolites in allantoic fluid of the chicken embryo in the 9th incubation day without any chemical or physical sample separation. The result showed that superhigh spectral dispersion and sensitivity at 900 MHz are useful in directly analyzing a complex mixture, particularly in resolving the overlapped NMR resonances. In this study, we had assigned 61 metabolites and 26 chemical fragments in the allantoic fluid. The relative concentrations of the major metabolites were also measured. Among the assigned metabolites, some were detected by NMR in chicken embryo allantoic fluids for the first time. The biological functions of these compounds were briefly discussed. Authors' address: Maili Liu, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China  相似文献   
138.
袁都奇 《物理学报》2006,55(4):1634-1638
根据由赝势法得到的非理想玻色气体的自由能和状态方程,研究了相互作用对凝聚温度的影响.从热力学角度揭示了存在引力作用时定压热容量、等温压缩系数、定压膨胀系数的反常热力学特性.研究了引力作用下玻色气体系统的不稳定性,给出了不稳定性的温度判据和粒子数密度判据. 关键词: 相互作用 玻色气体 热力学性质 不稳定性判据  相似文献   
139.
针对磷化铟(InP)复合沟道高电子迁移率晶体管(HEMT)的特点,对常规单沟道HEMT的小信号物理模型进行了修正,提出了一种新的用于复合沟道HEMT的小信号物理模型,用商用器件模拟软件ISE(integrated systems engineering)对其进行了仿真验证,对比了实测和仿真的I-V特性及转移特性曲线,重点研究了在InGaAs/InP双层沟道中考虑量子效应后的电场和电流密度随着不同栅电压的变化趋势,研究结果表明,由于在沟道中存在量子效应,在栅下靠源端低电场区域,电流主要分布在InGaAs沟道 关键词: 高电子迁移率晶体管 复合沟道 物理模型 磷化铟  相似文献   
140.
In this paper, novel interleavers using circular cavities (CC) in a Mach-Zehnder interferometer (MZI) has been presented and demonstrated for the first time, in which CCs act as phase dispersive mirrors which exhibit a periodic dependence on the frequency of light. Three implementation schemes have been proposed and investigated. Theoretical analysis shows the spectral characteristics of each scheme in a 50-GHz channel spacing application. Furthermore, the chromatic dispersion (CD) of each output comb can be flattened within passband by appending an additional CC. The result shows that the proposed designs with novel interferometer technique can simultaneously provide flat top passbands, high isolation stopband and low CD value as well.  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