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   6834篇
  免费   1275篇
  国内免费   470篇
化学   3676篇
晶体学   140篇
力学   139篇
综合类   31篇
数学   146篇
物理学   4447篇
  2024年   18篇
  2023年   52篇
  2022年   117篇
  2021年   157篇
  2020年   189篇
  2019年   165篇
  2018年   174篇
  2017年   194篇
  2016年   239篇
  2015年   221篇
  2014年   315篇
  2013年   548篇
  2012年   399篇
  2011年   507篇
  2010年   338篇
  2009年   424篇
  2008年   376篇
  2007年   407篇
  2006年   393篇
  2005年   341篇
  2004年   312篇
  2003年   317篇
  2002年   319篇
  2001年   242篇
  2000年   270篇
  1999年   193篇
  1998年   207篇
  1997年   128篇
  1996年   121篇
  1995年   86篇
  1994年   99篇
  1993年   89篇
  1992年   75篇
  1991年   47篇
  1990年   49篇
  1989年   28篇
  1988年   40篇
  1987年   34篇
  1986年   27篇
  1985年   24篇
  1984年   31篇
  1983年   22篇
  1982年   31篇
  1981年   43篇
  1980年   41篇
  1979年   64篇
  1978年   40篇
  1977年   9篇
  1974年   4篇
  1973年   4篇
排序方式: 共有8579条查询结果,搜索用时 15 毫秒
51.
磁电子学器件应用原理   总被引:13,自引:0,他引:13  
蔡建旺 《物理学进展》2006,26(2):180-227
本文介绍几种重要的磁电子器件的基本结构和工作原理,包括巨磁电阻与隧穿磁电阻传感器、巨磁电阻隔离器、巨磁电阻与隧穿磁电阻硬盘读出磁头、磁电阻随机存取存储器、自旋转移磁化反转与微波振荡器。自旋晶体管作为未来磁电子学或自旋电子学时代的基本元素,目前大都还处在概念型阶段,本文也将对几种自旋晶体管的大致原理作简要介绍。  相似文献   
52.
Novel oxyfluoride glasses are developed with the composition of 30SiO2-15Al2O3-28PbF2-22CdF2-0.1TmF3 - xYbF3 - (4.9 - x) AlF3(x=0, 0.5, 1.0, 1.5, 2.0) in tool fraction, Furthermore, the upconversion luminescence characteristics under a 970nm excitation are investigated. Intense blue, red and near infrared luminescences peaked at 453nm, 476nm, 647nm and 789nm, which correspond to the transitions of Tm^3+: ^1D2 →^3F4, ^1G4 →^3H6, ^1G4 →^3F4, and ^3H4 →^3H6, respectively, are observed. Due to the sensitization of Yb^3+ ions, all the upconversion luminescence intensities are enhanced considerably with Yb^3+ concentration increasing. The upconversion mechanisms are discussed based on the energy matching rule and quadratic dependence on excitation power. The results indicate that the dominant mechanism is the excited state absorption for those upconversion emissions.  相似文献   
53.
杨光  P. V. Santos 《物理学报》2006,55(8):4327-4331
结合声表面波和光致发光谱在低温(15K)下对非故意掺杂的GaAs(110)量子阱结构的发光特性进行了研究.实验结果表明,由于声表面波的作用GaAs(110)量子阱的发光强度减弱,并且其对应的重空穴能级出现了分裂的现象,当施加的声波强度Prf达到20dBm时,能级分裂ΔE达到了10meV.进一步讨论了声表面波对GaAs(110)量子阱圆偏振光自旋注入的影响. 关键词: 发光 GaAs量子阱 声表面波 自旋极化  相似文献   
54.
在Li2O-Al2O3-SiO2系统玻璃中掺入少量晶核剂TiO2,ZrO2,P2O5,再掺入稀土离子和过渡金属离子作为着色剂,在高温下溶制得到彩色透明玻璃,对上述玻璃进行微晶化处理,用差热分析(DTA)确定其晶化温度,测定与讨论了所获彩色透明微晶玻璃在紫外波段至近红外波段的吸收光谱特性,研究结果表明,玻璃微晶化后,由于基质玻璃对光的微弱散射,引起吸收的增强,但不改变稀土离子和过渡金属离子的本征吸收峰位。  相似文献   
55.
二维磁结构的扫描隧道显微术研究   总被引:1,自引:1,他引:0  
孙霞  王兵  王丽娟  吴自勤 《物理》2002,31(9):572-576
文章介绍了近年来利用扫描隧道显微术(STM)对表面和薄膜磁结构的研究进展。二维或表面磁结构可以通过在非磁性单晶上外延磁性单原子层薄膜形成,也可以在清洁的磁性单晶表面形成。利用磁性的STM针尖可以观测到原子分辨的表面磁结构。这将增进人们从纳米尺度对磁性的理解,并推动磁电子学的发展。  相似文献   
56.
This paper describes development of the optical current transducers using flint glass fiber as the Faraday effect sensing element. Excellent polarization properties of the fiber with low birefringence are described, and the design and test data of a current transducer using the fiber manufactured for use in electric power facilities are reviewed. Experimental results on flexible characteristics of a scheme with round trip light transmission in the fiber is also reported.  相似文献   
57.
The model considered is a d=2 disordered Ising system on a square lattice with nearest neighbor interaction. The disorder is induced by layers (rows) of spins, randomly located, which are frozen in an antiferromagnetic order. It is assumed that all the vertical couplings take the same positive value J v, while all the horizontal couplings take the same positive value J h. The model can be exactly solved and the free energy is given as a simple explicit expression. The zero-temperature entropy can be positive because of the frustration due to the competition between antiferromagnetic alignment induced by the quenched layers and ferromagnetic alignment due to the positive couplings. No phase transition is found at finite temperature if the layers of frozen spins are independently distributed, while for correlated disorder one finds a low-temperature phase with some glassy properties.  相似文献   
58.
Creep and differential scanning calorimetry (DSC) measurements have been used to study the physical aging behavior of a polyetherimide. Isothermal aging temperatures ranged from 160°C to Tg with aging times ranging from 10 min to 8 days. The only measurable effect of physical aging on the short-time creep curves is a shift of the creep compliance to longer times. Andrade plots of the compliance versus the cube root of time are linear at short times with the slope β decreasing with increasing aging time to a constant value once equilibrium is reached. Log β3 is related directly to the degree to which the creep curves shift to longer times with physical aging, and is used in this work as a measure of physical aging. A reduced curve of log β3 versus log aging time is obtained for the aging temperatures investigated by appropriate vertical and horizontal shifts. The enthalpy change during aging increases linearly with the logarithm of the aging time, ta, leveling off at equilibrium at values which increase with decreasing aging temperature. Hence, both nonequilibrium and equilibrium temperature shift factors can be calculated from the DSC data. Good agreement is observed between the equilibrium temperature shift factors obtained from the creep and DSC data. The temperature dependence of the nonequilibrium temperature shift factors is found to be an order of magnitude smaller than that of the equilibrium shift factors. The time scales to reach equilibrium for enthalpy and for mechanical measurements are found to be the same within experimental error. © 1995 John Wiley & Sons, Inc.  相似文献   
59.
This review paper deals with an overview of molecule-based magnetism as a rapidly developing interdisciplinary field, topological symmetry rule as the first principle of spin alignment in organic open-shell systems in the ground state, the proposal of organic through-bond 1D and 2D ferro- and superparamagnets and the detection of the first organic high-spin molecule, m-phenylenebis(phenylmethylene) in the quintet ground state (S = 2), followed by extended organic high-spin systems with π-conjugation such as aromatic hydrocarbons having S = 3, 4, 5. The paper also describes a theoretical approach to the understanding of electronic spin structures of organic high-spin molecules by invoking both Heisenberg and Hubbard model Hamiltonians, weakly interacting intramolecular high-spin systems from both experimental and theoretical sides, the spin density distribution of the first organic high-spin molecule in terms of electron- nuclear multiple resonance spectroscopy and the detection and characterization of ionic high-spin hydrocarbons, emphasizing the establishment of high spin chemistry underlying organic molecular magnetism.  相似文献   
60.
利用融合蒸发反应116Cd(14N,4n)126Cs布居了126Cs的高自旋态.观测到了100多条新的γ跃迁和相应的能级,建立了双奇核126Cs由9个转动带构成的能级纲图.尝试性地指定了大部分能级的自旋和宇称以及各转动带的Nilsson单粒子组态.极大地丰富了已有的实验结果.  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