全文获取类型
收费全文 | 7232篇 |
免费 | 944篇 |
国内免费 | 241篇 |
专业分类
化学 | 146篇 |
晶体学 | 10篇 |
力学 | 218篇 |
综合类 | 21篇 |
数学 | 173篇 |
物理学 | 1183篇 |
无线电 | 6666篇 |
出版年
2024年 | 56篇 |
2023年 | 193篇 |
2022年 | 223篇 |
2021年 | 180篇 |
2020年 | 139篇 |
2019年 | 158篇 |
2018年 | 101篇 |
2017年 | 169篇 |
2016年 | 243篇 |
2015年 | 264篇 |
2014年 | 522篇 |
2013年 | 428篇 |
2012年 | 515篇 |
2011年 | 530篇 |
2010年 | 544篇 |
2009年 | 552篇 |
2008年 | 684篇 |
2007年 | 455篇 |
2006年 | 468篇 |
2005年 | 440篇 |
2004年 | 344篇 |
2003年 | 255篇 |
2002年 | 188篇 |
2001年 | 128篇 |
2000年 | 113篇 |
1999年 | 91篇 |
1998年 | 85篇 |
1997年 | 61篇 |
1996年 | 61篇 |
1995年 | 61篇 |
1994年 | 34篇 |
1993年 | 32篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有8417条查询结果,搜索用时 828 毫秒
991.
992.
A Brownian microscopic heat engine with a particle hopping on a one-dimensional lattice driven by a discrete and periodic temperature field in a periodic sawtooth potential is investigated. In order to clarify the underlying physical pictures of the heat engine, the heat flow via the potential energy and the kinetic energy of the particles are considered simultaneously. Based on describing the jumps among the three states, the expressions of the efficiency and power output of the heat engine are derived analytically. The general performance characteristic curves are plotted by numerical calculation. It is found that the power output-efficiency curve is a loop-shaped one, which is similar to one for a real irreversible heat engine. The influence of the ratio of the temperature of the hot and cold reservoirs and the sawtooth potential on the maximum efficiency and power output is analyzed for some given parameters. When the heat flows via the kinetic energy is neglected, the power output-efficiency curve is an open-shaped one, which is similar to one for an endroeversible heat engine. 相似文献
993.
Driven dynamics of a two-dimensional Frenkel-Kontorova model is studied in the paper. In our numerical simulations, it is found that the movement direction of the center of mass is not consistent with that of the external driving force except for some special symmetric directions at the lower driving force. Our results also indicate that the movement direction of the center of mass strongly depends on both the magnitude and the direction of the external driving force as well as the misfit angle between two layers. 相似文献
994.
Magnetic bunch compressor is one of the key technologies on the path to next generation accelerator driven facilities. In this paper we report the design principles and the first experimental research of the bunch compressor developed at Chinese Academy of Engineering Physics (CAEP). The length of the bunch after compressor is found to be about 0.7 ps (rms) and the peak current exceeds 500 A when operated in the optimized condition. The sensitivity of the bunch length on the phase of the acceleration field and magnetic field of the bunch compressor was also measured and analyzed. 相似文献
995.
A one-dimensional electrostatic particle-in-cell simulation is performed to study electrostatic wave excitation due to an electron beam in a plasma system. The excited fundamental and harmonic waves are analyzed with the fast Fourier transformation and the wavelet transformation. The second harmonic is suggested to be generated by wave-wave coupling during the nonlinear evolution, which involves forward propagating and backward propagating Langmuir waves. Furthermore, the background electrons may be heated and accelerated by the electrostatic waves. 相似文献
996.
Empirical observations indicate that the interevent time distribution of human actions exhibits heavy-tailed features. The queuing model based on task priorities is to some extent successful in explaining the origin of such heavy tails, however, it cannot explain all the temporal statistics of human behavior especially for the daily entertainments. We propose an interest-driven model, which can reproduce the power-law distribution of interevent time. The exponent can be analytically obtained and is in good accordance with the simulations. This model well explains the observed relationship between activities and power-law exponents, as reported recently for web-based behavior and the instant message communications. 相似文献
997.
Bending and first flexural mode vibration behavior of electrostatic actuated nanometer-sized interdigitated cantilever arrays are characterized under vacuum conditions. The pull-in'' effect in dc driving and the hard spring effect'' in ac driving are observed. A mass sensitivity of 20 fg is expected for our devices due to the ultra-small mass of the arm and relative high Q factor. The mass-spring lump model combined with Green's function method is used to fit the dc driving behaviors including the pull-in voltage. For the ac driving case, the polynomial expansion of the capacitive force is used in the model. The successfully fittings of the pull-in voltage and the hard spring effect prove that our simulation method could be used for guiding the geometrical design of cantilever-based sensors. 相似文献
998.
A new simple model of self-driven particles in scale-free networks is introduced to understand the emergence of condensation in the natural world. In the model, at each time step, particles are driven to choose their next habitats according to the particle numbers at both the present habitats and neighbors. It is found that the hub effect results in the condensation. The present numerical results as well as the theoretical analysis of condensation transition show the criterion of condensation. Both simulations and theoretical analysis display that there are three phases for different hopping probabilities δ: non-condensation (δ〈δc), partial condensation (δc≤ δ〈1), and complete condensation (δ≥δc'= 1), and the mean occupation particle number at the stationary state is also obtained. Moreover, the noise effect on self-driven particles is studied, and it makes particle numbers at nodes tend towards being identical. 相似文献
999.
通常真空管放大器的输出阻抗都是按照扬声器的标称阻抗的值来设计的,但是在实际使用时扬声器的阻抗并不是一个固定的值,其值随频率变化并且变化量还很大,从而导致放大器的驱动条件不再是恒定不变的,本文将对放大器的输出阻抗对音箱的声压特性的影响进行探讨,通过改变真空管放大器和晶体管放大器的负载测量放大器的驱动特性,弄清楚放大器输出阻抗对音箱音质的影响。 相似文献
1000.
绿色创新与阳光工程已成为一种社会责任与人文理念;节能减排、绿色创新与绿色阳光工程与ICT的战略发展密切相关联。 相似文献