全文获取类型
收费全文 | 4517篇 |
免费 | 596篇 |
国内免费 | 673篇 |
专业分类
化学 | 802篇 |
晶体学 | 32篇 |
力学 | 197篇 |
综合类 | 102篇 |
数学 | 225篇 |
物理学 | 1038篇 |
综合类 | 3390篇 |
出版年
2024年 | 32篇 |
2023年 | 107篇 |
2022年 | 119篇 |
2021年 | 112篇 |
2020年 | 78篇 |
2019年 | 116篇 |
2018年 | 139篇 |
2017年 | 95篇 |
2016年 | 102篇 |
2015年 | 113篇 |
2014年 | 272篇 |
2013年 | 230篇 |
2012年 | 240篇 |
2011年 | 270篇 |
2010年 | 233篇 |
2009年 | 287篇 |
2008年 | 265篇 |
2007年 | 296篇 |
2006年 | 236篇 |
2005年 | 220篇 |
2004年 | 217篇 |
2003年 | 173篇 |
2002年 | 153篇 |
2001年 | 141篇 |
2000年 | 145篇 |
1999年 | 140篇 |
1998年 | 110篇 |
1997年 | 90篇 |
1996年 | 109篇 |
1995年 | 118篇 |
1994年 | 80篇 |
1993年 | 78篇 |
1992年 | 85篇 |
1991年 | 58篇 |
1990年 | 76篇 |
1989年 | 80篇 |
1988年 | 60篇 |
1987年 | 48篇 |
1986年 | 42篇 |
1985年 | 40篇 |
1984年 | 38篇 |
1983年 | 28篇 |
1982年 | 16篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 14篇 |
1965年 | 8篇 |
1961年 | 3篇 |
1958年 | 3篇 |
排序方式: 共有5786条查询结果,搜索用时 15 毫秒
981.
本文考虑如下一类含两项分数阶导数的半线性分数阶微分方程解的存在性问题:
(_^c)D_t^α u(t)+ (_^c)D_t^β u(t)=f(t,u(t) ),0β>0, (_^c)D_t^β u(t)为Caputo分数阶导数. 我们利用Schauder不动点定理证明了在适当条件下解的存在性,所得结果改进了已有结论。 相似文献
982.
本论述结合某厂两套微球装置中橡胶带式过滤机的应用现状,从设备材料、设计、制造等方面,分析滑台与真空室堵塞、电气及仪表、胶带托辊及转向辊轴承座三类故障原因,结合实际工况,提出真空室、滑台堵塞故障处理方案,设计胶带托辊及转向辊轴承座改进措施,通过检修维护方案和改进措施的实施,减少了此类设备故障发生.通过实际应用发现,本论述方案解决了DU型橡胶带式过滤机在催化剂微球生产中的适应性问题,提升了设备运行周期,降低了维护费用,为同类型设备在催化剂生产应用中提供一定的参考价值. 相似文献
983.
碳化硅(SiC)由于性能优异,已广泛应用于核技术领域.在辐照环境下,载能入射粒子可使材料中的原子偏离晶体格点位置,进而产生过饱和的空位、间隙原子、错位原子等点缺陷,这些缺陷将改变材料的热物性能,劣化材料的服役性能.因此,本文利用平衡分子动力学方法(Green-Kubo方法)采用Tersoff型势函数研究了点缺陷对立方碳化硅(β-SiC或3C-SiC)热传导性能的影响规律.研究过程中考虑的点缺陷包括:Si间隙原子(SiⅠ)、Si空位(SiⅤ)、Si错位原子(SiC)、C间隙原子(CⅠ)、C空位(CⅤ)和C错位原子(CSi).研究结果表明,热导率(λ)随点缺陷浓度(c)的增加而减小.在研究的点缺陷浓度范围(点缺陷与格点的比例范围为0.2%—1.6%),额外热阻率(ΔR-Rdefect-Rperfect,R=1/λ,Rdefect为含缺陷材料的热阻率,Rperfec... 相似文献
984.
Shou-Kuan Zhao 《中国物理 B》2022,31(3):30307-030307
The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used. 相似文献
985.
Hai-Long Liu 《中国物理 B》2022,31(11):110306-110306
A single-photon interferometer is a fundamental element in quantum information science. In most previously reported works, single-photon interferometers use an active feedback locking system to stabilize the relative phase between two arms of the interferometer. Here, we use a pair of beam displacers to construct a passively stable single-photon interferometer. The relative phase stabilization between the two arms is achieved by stabilizing the temperature of the beam displacers. A purely polarized single-photon-level pulse is directed into the interferometer input port. By analyzing and measuring the polarization states of the single-photon pulse at the output port, the achieved polarization fidelity of the interferometer is about 99.1 ±0.1%. Our passively stabilized single-photon interferometer provides a key element for generating high-fidelity entanglement between a photon and atomic memory. 相似文献
986.
Magnetic susceptibility, specific heat, and neutron powder diffraction measurements have been performed on polycrystalline Li$_{2}$Co(WO$_{4}$)$_{2}$ samples. Under zero magnetic field, two successive magnetic transitions at $T_{\rm N1}\sim 9.4$ K and $T_{\rm N2}\sim 7.4$ K are observed. The magnetic ordering temperatures gradually decrease as the magnetic field increases. Neutron diffraction reveals that Li$_{2}$Co(WO$_{4}$)$_{2}$ enters an incommensurate magnetic state with a temperature dependent $\bm k$ between $T_{\rm N1}$ and $T_{\rm N2}$. The magnetic propagation vector locks-in to a commensurate value $\bm k = (1/2, 1/4, 1/4)$ below $T_{\rm N2}$. The antiferromagnetic structure is refined at 1.7 K with Co$^{2+}$ magnetic moment 2.8(1) $\mu_{\rm B}$, consistent with our first-principles calculations. 相似文献
987.
Studies of sustained oscillations on complex networks with excitable node dynamics received much interest in recent years. Although an individual unit is non-oscillatory, they may organize to form various collective oscillatory patterns through networked connections. An excitable network usually possesses a number of oscillatory modes dominated by different Winfree loops and numerous spatiotemporal patterns organized by different propagation path distributions. The traditional approach of the so-called dominant phase-advanced drive method has been well applied to the study of stationary oscillation patterns on a network. In this paper, we develop the functional-weight approach that has been successfully used in studies of sustained oscillations in gene-regulated networks by an extension to the high-dimensional node dynamics. This approach can be well applied to the study of sustained oscillations in coupled excitable units. We tested this scheme for different networks, such as homogeneous random networks, small-world networks, and scale-free networks and found it can accurately dig out the oscillation source and the propagation path. The present approach is believed to have the potential in studies competitive non-stationary dynamics. 相似文献
988.
989.
与几何凸函数有关的一些单调函数的构造 总被引:4,自引:0,他引:4
本文利用文献[1]中的有关几何凸函数的不等式,来完成一些单调函数的构造,从而更好地说明几何凸函数的内在性质和特点. 相似文献
990.