全文获取类型
收费全文 | 843篇 |
免费 | 242篇 |
国内免费 | 140篇 |
专业分类
化学 | 80篇 |
晶体学 | 13篇 |
力学 | 256篇 |
综合类 | 1篇 |
数学 | 27篇 |
物理学 | 848篇 |
出版年
2023年 | 19篇 |
2022年 | 32篇 |
2021年 | 31篇 |
2020年 | 24篇 |
2019年 | 27篇 |
2018年 | 26篇 |
2017年 | 37篇 |
2016年 | 32篇 |
2015年 | 23篇 |
2014年 | 40篇 |
2013年 | 60篇 |
2012年 | 50篇 |
2011年 | 61篇 |
2010年 | 60篇 |
2009年 | 60篇 |
2008年 | 66篇 |
2007年 | 63篇 |
2006年 | 56篇 |
2005年 | 58篇 |
2004年 | 30篇 |
2003年 | 43篇 |
2002年 | 54篇 |
2001年 | 51篇 |
2000年 | 30篇 |
1999年 | 32篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 24篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有1225条查询结果,搜索用时 15 毫秒
101.
102.
Effect of parameters on the rubbing condition of an unbalanced rotor system with initial permanent deflection 总被引:1,自引:0,他引:1
Xiaoyao Shen Jiuhong Jia Mei Zhao 《Archive of Applied Mechanics (Ingenieur Archiv)》2007,77(12):883-892
A rotor-stator rubbing Jeffcott model of a rotor system with mass unbalance including the mass eccentricity and the initial
permanent deflection was set up and the corresponding governing motion equation was derived by d’Alembert principle. Through
the analytical method, the rubbing condition was analyzed. Whether the rub would happen and when the rub would happen were
well solved. The amplitude of the rotor center was calculated, and the rubbing factor was introduced to determine whether
the rub would happen or not for all rotating speeds. Rubbing speeds when rub began to happen were obtained. Parameters such
as the mass eccentricity, the initial permanent deflection, damping coefficients, and the phase angle between the mass eccentricity
and the permanent deflection were used to analyze their effect on the rubbing condition. Results were obtained and could be
used to prevent the rubbing fault or decrease the damage of the rub and diagnose or balance the initial permanent deflection
fault. 相似文献
103.
超导量子干涉仪(SQUID)放大器具有低输入阻抗、低噪声、低功耗等优点, 目前被广泛用于微弱信号的检测领域. 与其他工艺相比, Nb/Al-AlOx/Nb结构的约瑟夫森结具有相对较高的转变温度(Tc)、高的磁通电压调制系数以及良好的热循环能力、较宽的临界电流范围, 因此是制备SQUID放大器的很好选择. 设计并制作了欠阻尼、过阻尼约瑟夫森结以及具有Washer型输入线圈的单SQUID放大器, 通过在He3制冷机3 K温区下对器件电流-电压特性进行测量, 得到良好的结I-V特性曲线、SQUID调制特性, 初步实现利用SQUID进行放大作用, 并计算了SQUID的电流分辨率. 此项工作对于超导转变边沿传感器读出电路的实现具有重要的意义. 相似文献
104.
A high-order upwind scheme has been developed to capture the vortex wake of a helicopter rotor in the hover based on chimera grids. In this paper, an improved fifth-order weighted essentially non-oscillatory (WENO) scheme is adopted to interpolate the higher-order left and right states across a cell interface with the Roe Riemann solver updating inviscid flux, and is compared with the monotone upwind scheme for scalar conservation laws (MUSCL). For profitably capturing the wake and enforcing the period boun... 相似文献
105.
A nonlinear model of a low pressure cylinder-generator rotor system is presented to study sub-synchronous resonance and combined
resonance. Analytical results are obtained by an averaging method. Transition sets and bifurcation diagrams are obtained based
on the singularity theory for the two-state variable system. The bifurcation characteristics are analyzed to provide a basis
for the optimal design and fault diagnosis of the rotor system. Finally, the theoretical results are verified with the numerical
results. 相似文献
106.
In this article we discuss the physical principles behind new quantum devices and materials that require some form of nanoscale fabrication. The two systems we discuss are superconducting quantum circuits and nanomechanical resonators. Both systems involve many-body systems of a special kind in which particular collective degrees of freedom can be factored out of the microscopic dynamics and subject to quantum control. We discuss applications to precision metrology. 相似文献
107.
Hongxin Wang Anthony T. Young Jinghua Guo Stephen P. Cramer Stephan Friedrich Artur Braun Weiwei Gu 《Journal of synchrotron radiation》2013,20(4):614-619
X‐ray absorption and scattering spectroscopies involving the 3d transition‐metal K‐ and L‐edges have a long history in studying inorganic and bioinorganic molecules. However, there have been very few studies using the M‐edges, which are below 100 eV. Synchrotron‐based X‐ray sources can have higher energy resolution at M‐edges. M‐edge X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) could therefore provide complementary information to K‐ and L‐edge spectroscopies. In this study, M2,3‐edge XAS on several Co, Ni and Cu complexes are measured and their spectral information, such as chemical shifts and covalency effects, are analyzed and discussed. In addition, M2,3‐edge RIXS on NiO, NiF2 and two other covalent complexes have been performed and different d–d transition patterns have been observed. Although still preliminary, this work on 3d metal complexes demonstrates the potential to use M‐edge XAS and RIXS on more complicated 3d metal complexes in the future. The potential for using high‐sensitivity and high‐resolution superconducting tunnel junction X‐ray detectors below 100 eV is also illustrated and discussed. 相似文献
108.
采用制冷机直接冷却的低温超导磁体系统与传统液氮冷却方式相比,具有轻便紧凑、运行简单、维护方便、可长时间连续运行等优点;而脉管制冷由于冷端无运动部件,与传统的G-M制冷机相比,具有结构简单、运行可靠、振动小等优点.本文结合我们在液氮温区脉管制冷方面的技术,从漏热和经济性两方面探讨了将脉管制冷直接用于冷却一个5特斯拉NbTi低温超导磁体的可行性,为后期系统的搭建奠定基础. 相似文献
109.
W. Hanke O. Schmitt H. Endres R. Kleiner P. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):465-471
A quantitative analysis of a microscopic model for the intrinsic Josephson effect in high-temperature superconductors based
on interlayer tunneling is presented both within a mean-field BCS evaluation and a numerically essentially exact Quantum Monte-Carlo
study. The pairing correlations in the CuO2-planes are modelled by a 2D Hubbard model with attractive interaction, a model which accounts well for some of the observed
features such as the short planar coherence length. The stack of Hubbard planes is arranged on a torus, which is threaded
by a magnetic flux. The current perpendicular to the planes is calculated as a function of applied flux (i.e. the phase), and - after careful elimination of finite-size effects due to single-particle tunneling - found to display a
sinusoidal field dependence in accordance with interlayer Josephson tunneling. Studies of the temperature dependence of the
supercurrent reveal at best a mild elevation of the Josephson transition temperature compared to the planar Kosterlitz-Thouless
temperature. These and other results on the dependence of the model parameters are compared with a standard BCS evaluation.
Received: 24 February 1998 / Revised: 28 April 1998 / Accepted: 23 June 1998 相似文献
110.
P N Ostroumov 《Pramana》2002,59(6):895-913
The Nuclear Science Community in the Unites States has unanimously concluded that developments in both nuclear science and
its supporting technologies make building a world-leading Rare-Isotope Accelerator (RIA) facility for production of radioactive
beams the top priority. The RIA development effort involves several US Laboratories (ANL, JLAB, LBNL, MSU, ORNL). The RIA
facility includes a CW 1.4 GeV driver LINAC and a 100 MV post-accelerator both based on superconducting (SC) cavities operating
at frequencies from 48 MHz to 805 MHz. An initial acceleration in both LINACs is provided by room temperature RFQs. The driver
LINAC is designed for acceleration of any ion species; from protons up to 900 MeV to uranium up to 400 MeV/u. The novel feature
of the driver LINAC is an acceleration of multiple charge-state heavy-ion beams in order to achieve 400 kW beam power. Basic
design concepts of the driver LINAC are given. Several new conceptual solutions in beam dynamics, room temperature and SC
accelerating structures for heavy ion accelerator applications are discussed. 相似文献