全文获取类型
收费全文 | 17044篇 |
免费 | 2711篇 |
国内免费 | 2528篇 |
专业分类
化学 | 13473篇 |
晶体学 | 217篇 |
力学 | 697篇 |
综合类 | 256篇 |
数学 | 1759篇 |
物理学 | 5881篇 |
出版年
2024年 | 46篇 |
2023年 | 284篇 |
2022年 | 516篇 |
2021年 | 546篇 |
2020年 | 639篇 |
2019年 | 676篇 |
2018年 | 565篇 |
2017年 | 543篇 |
2016年 | 890篇 |
2015年 | 896篇 |
2014年 | 993篇 |
2013年 | 1370篇 |
2012年 | 1489篇 |
2011年 | 1557篇 |
2010年 | 1108篇 |
2009年 | 1104篇 |
2008年 | 1190篇 |
2007年 | 1070篇 |
2006年 | 1056篇 |
2005年 | 950篇 |
2004年 | 751篇 |
2003年 | 668篇 |
2002年 | 718篇 |
2001年 | 488篇 |
2000年 | 439篇 |
1999年 | 336篇 |
1998年 | 214篇 |
1997年 | 192篇 |
1996年 | 182篇 |
1995年 | 148篇 |
1994年 | 130篇 |
1993年 | 102篇 |
1992年 | 73篇 |
1991年 | 58篇 |
1990年 | 49篇 |
1989年 | 45篇 |
1988年 | 27篇 |
1987年 | 41篇 |
1986年 | 25篇 |
1985年 | 27篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1957年 | 5篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
81.
The improved range Doppler algorithm is proposed to abate the trade-off between resolutions and depth of focus in spectral domain optical coherence tomography.By considering the finite beam width and the shape of the wavefronts produced by the Gaussian beam,a physical diffraction model is presented to simulate the light propagation process in the sample.The two-dimensional processing of the spectrum data is decomposed into two one-dimensional processings of Stolt transform and matched filter.Experimental results show that image reconstruction can be achieved.The transverse and axial resolutions are both improved significantly,especially in the out-of-focus range,and the resolutions are almost equivalent throughout the entire region of interest. 相似文献
82.
A three-dimensional mathematical model is developed to examine the flow of nonlinear thermal radiation Oldroyd-B nanofluid past a bidirectional linearly stretched surface in a porous medium. The flow is induced by temperature dependent thermal conductivity, chemical reaction and convective heat and mass conditions. Novel characteristics of Brownian motion and thermophoresis are accompanied by magnetohydrodynamic and heat generation/absorption. Self-similar transformations are employed to convert the system of nonlinear partial differential equations to a system of ordinary differential equations with high nonlinearity and are solved by strong analytic technique named as Homotopy Analysis method (HAM). Effects of varied arising parameters on involved distributions are reflected through graphical illustrations. From this study, it is perceived that strong magnetic field hinders the fluid's motion and leads to rise in temperature that eventually lowers heat transfer rate from the surface. Further, decrease in heat transfer rate is also observed for enhanced values of thermal radiation parameter. To validate our results, a comparison with already published paper in limiting case is also given and results are found in excellent oncurrence; hence reliable results are being presented. 相似文献
83.
The energy recovery linac test facility (ERL-TF), which is a compact ERL-FEL (free electron laser) two-purpose machine, was proposed at the Institute of High Energy Physics, Beijing. As one important component of the ERL-TF, the photo-injector that started with a photocathode direct-current gun has been designed. In this paper, optimization of the injector beam dynamics in low-charge operation mode is performed with iterative scans using Impact-T. In addition, the dependencies between the optimized beam quality and the initial offset at cathode and element parameters are, investigated. The tolerance of alignment and rotation errors is also analyzed. 相似文献
85.
Solitons and intrinsic localized modes in a one-dimensional antiferromagnetic chain 总被引:3,自引:0,他引:3 下载免费PDF全文
By use of the Hartree approximation and the method of multiple scales, we
investigate quantum solitons and intrinsic localized modes in a
one-dimensional antiferromagnetic chain. It is shown that there exist
solitons of two different quantum frequency bands: i.e., magnetic optical
solitons and acoustic solitons. At the boundary of the Brillouin zone, these
solitons become quantum intrinsic localized modes: their quantum
eigenfrequencies are below the bottom of the harmonic optical frequency band
and above the top of the harmonic acoustic frequency band. 相似文献
86.
87.
The spin current in a parabolically confined semiconductor
heterojunction quantum wire with Dresselhaus spin--orbit coupling is
theoretically studied by using the perturbation method. The formulae
of the elements for linear and angular spin current densities are
derived by using the recent definition for spin current based on spin
continuity equation. It is found that the spin current in this
Dresselhaus spin--orbit coupling quantum wire is antisymmetrical,
which is different from that in Rashba model due to the difference in
symmetry between these two models. Some numerical examples for the
result are also demonstrated and discussed. 相似文献
88.
A series of a-Si:H films are deposited by hot wire assisted microwave
electron cyclotron resonant chemical vapour deposition
(HW-MWECR-CVD), subsequently exposed under simulated illumination for
three hours. This paper studies the microstructure change during
illumination by Fourier Transformation Infrared (FTIR) spectra. There
are two typical transformation tendencies of microstructure after
illumination. It proposes a model of light induced structural change
based on the experimental results. It is found that all samples
follow the same mechanism during illumination, and intrinsic
structure of samples affect the total H content. 相似文献
89.
90.
紧凑型PFN-Marx脉冲发生器中,级与级之间存在着较大的寄生电容,该电容和PFN节电感构成了寄生传输线。对两种排布方式下的寄生传输线的放电过程进行了简单分析,重点开展了双列排布方式下全电路仿真模拟,对负载类型、寄生电容、负载电感等参数对输出波形的影响进行了计算,得到了二极管负载会在波形前沿上造成下降、寄生电容大小决定振荡频率、负载电感放大振荡幅值等结论。开展的PFN-Marx实验研究也进一步验证了上述分析结果。根据分析,提出了一种有效抑制输出波形振荡的方法,从电路上进行了仿真验证,进一步实验证实了该方法的有效性。 相似文献