全文获取类型
收费全文 | 8703篇 |
免费 | 917篇 |
国内免费 | 687篇 |
专业分类
化学 | 2644篇 |
晶体学 | 61篇 |
力学 | 623篇 |
综合类 | 52篇 |
数学 | 840篇 |
物理学 | 6087篇 |
出版年
2024年 | 24篇 |
2023年 | 91篇 |
2022年 | 127篇 |
2021年 | 112篇 |
2020年 | 195篇 |
2019年 | 168篇 |
2018年 | 173篇 |
2017年 | 235篇 |
2016年 | 318篇 |
2015年 | 276篇 |
2014年 | 488篇 |
2013年 | 816篇 |
2012年 | 414篇 |
2011年 | 726篇 |
2010年 | 508篇 |
2009年 | 619篇 |
2008年 | 607篇 |
2007年 | 600篇 |
2006年 | 510篇 |
2005年 | 375篇 |
2004年 | 349篇 |
2003年 | 333篇 |
2002年 | 317篇 |
2001年 | 272篇 |
2000年 | 296篇 |
1999年 | 208篇 |
1998年 | 192篇 |
1997年 | 136篇 |
1996年 | 103篇 |
1995年 | 119篇 |
1994年 | 84篇 |
1993年 | 84篇 |
1992年 | 79篇 |
1991年 | 50篇 |
1990年 | 39篇 |
1989年 | 60篇 |
1988年 | 38篇 |
1987年 | 31篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
81.
Hollow particles with interconnected cavities have been prepared by a simple modified suspension polymerization of acrylate monomers in the incorporation of a phase inversion process and polymerizable emulsifier. The morphology of particles has been characterized by scanning electron micrographs (SEMs). Based on observations made using an optical microscope equipped with a digital camera and SEM images of particles obtained under different conditions, the formation mechanisms for multiporous hollow particles are discussed. 相似文献
82.
M.Yu. Tretyakov V.V. Parshin M.A. Koshelev A.P. Shkaev A.F. Krupnov 《Journal of Molecular Spectroscopy》2006,238(1):91-97
Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′ka′, kc′-Jka, kc = 51,5-42,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 31,3-22,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given. 相似文献
83.
84.
85.
We consider a retrial queue with a finite buffer of size N, with arrivals of ordinary units and of negative units (which cancel one ordinary unit), both assumed to be Markovian arrival
processes. The service requirements are of phase type. In addition, a PHL,N bulk service discipline is assumed. This means that the units are served in groups of size at least L, where 1≤ L≤ N. If at the completion of a service fewer than L units are present at the buffer, the server switches off and waits until the buffer length reaches the threshold L. Then it switches on and initiates service for such a group of units. On the contrary, if at the completion of a service
L or more units are present at the buffer, all units enter service as a group. Units arriving when the buffer is full are not
lost, but they join a group of unsatisfied units called “orbit”. Our interest is in the continuous-time Markov chain describing
the state of the queue at arbitrary times, which constitutes a level dependent quasi-birth-and-death process. We start by
analyzing a simplified version of our queueing model, which is amenable to numerical calculation and is based on spatially
homogeneous quasi-birth-and-death processes. This leads to modified matrix-geometric formulas that reveal the basic qualitative
properties of our algorithmic approach for computing performance measures.
AMS Subject Classification: Primary 60K25 Secondary 68M20 90B22. 相似文献
86.
Low-temperature property investigation of the lead indium-niobate-lead nickel-niobate solid solution
Edward F AlbertaAmar S Bhalla 《Journal of Physics and Chemistry of Solids》2002,63(9):1759-1769
The complex perovskite solid solution (1−x) Pb(In1/2Nb1/2)O3-(x) Pb(Ni1/3Nb2/3)O3 has been successfully prepared by the Columbite precursor method. The temperature dependencies of the dielectric constant and pyroelectric coefficient were measured between −261 and 200 °C. Relaxor ferroelectric behavior has been noticed in all compositions across the solid solution. The room-temperature electrostrictive coefficient, Q33, was 1.83×10−2 C2/m4 for x=0.10. No room-temperature piezoelectric activity was detected; however, upon cooling to −261 °C the maximum coupling coefficients kp=29%, kt=11%, and k33=31% were observed for the composition x=1.00. 相似文献
87.
采用矩阵奇异值分解(singular value decomposition, SVD)的方法,对高温射频超导量子干涉仪(HTc rf-SQUID)采集到的单通道心磁信号进行处理.证明了对于近似周期性的心磁信号,在无参考噪声的情况下矩阵奇异值分解的方法与自适应窄带陷波相结合有较好的消除广谱噪声的效果.
关键词:
高温射频超导量子干涉仪
心磁信号
奇异值分解
噪声消除 相似文献
88.
89.
Non-Markovian Brownian motion in a periodic potential is studied by means of an electronic analogue simulator. Velocity spectra, the Fourier transforms of velocity autocorrelation functions, are obtained for three types of random force, that is, a white noise, an Ornstein—Uhlenbeck process, and a quasimonochromatic noise. The analogue results are in good agreement both with theoretical ones calculated with the use of a matrix-continued-fraction method, and with the results of digital simulations. An unexpected extra peak in the velocity spectrum is observed for Ornstein-Uhlenbeck noise with large correlation time. The peak is attributed to a slow oscillatory motion of the Brownian particle as it moves back and forth over several lattice spaces. Its relationship to an approximate Langevin equation is discussed. 相似文献
90.
Some hydrodynamic aspects of 3-phase inverse fluidized bed 总被引:2,自引:0,他引:2
Krishna S.V.S.R. Bandaru D.V.S. Murthy K. Krishnaiah 《中国颗粒学报》2007,5(5):351-356
Hydrodynamics of 3-phase inverse fluidized bed is studied experimentally using low density particles for different liquid and gas velocities. The hydrodynamic characteristics studied include pressure drop, minimum liquid and gas fluidization velocities and phase holdups. The minimum liquid fluidization velocity determined using the bed pressure gradient, decreases with increase in gas velocity. The axial profiles of phase holdups shows that the liquid holdup increases along the bed height, whereas the solid holdup decreases down the bed. However, the gas holdup is almost uniform in the bed. 相似文献