全文获取类型
收费全文 | 4510篇 |
免费 | 770篇 |
国内免费 | 620篇 |
专业分类
化学 | 1914篇 |
晶体学 | 48篇 |
力学 | 513篇 |
综合类 | 44篇 |
数学 | 730篇 |
物理学 | 2651篇 |
出版年
2024年 | 16篇 |
2023年 | 50篇 |
2022年 | 125篇 |
2021年 | 122篇 |
2020年 | 169篇 |
2019年 | 124篇 |
2018年 | 149篇 |
2017年 | 172篇 |
2016年 | 197篇 |
2015年 | 170篇 |
2014年 | 218篇 |
2013年 | 330篇 |
2012年 | 264篇 |
2011年 | 286篇 |
2010年 | 247篇 |
2009年 | 286篇 |
2008年 | 267篇 |
2007年 | 326篇 |
2006年 | 267篇 |
2005年 | 247篇 |
2004年 | 233篇 |
2003年 | 214篇 |
2002年 | 203篇 |
2001年 | 190篇 |
2000年 | 152篇 |
1999年 | 111篇 |
1998年 | 113篇 |
1997年 | 113篇 |
1996年 | 95篇 |
1995年 | 54篇 |
1994年 | 58篇 |
1993年 | 47篇 |
1992年 | 43篇 |
1991年 | 40篇 |
1990年 | 30篇 |
1989年 | 25篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 12篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1973年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有5900条查询结果,搜索用时 17 毫秒
21.
We demonstrate the potential of femtosecond two-color pulse interferometry for in vitro optical glucose monitoring, by dispersion of the group refractive index in a glucose solution sample with respect to a red-color
light and a blue-color light. By comparison with femtosecond one-color pulse interferometry, the basic performance of the
present system with regard to sensitivity, quantitativeness, and tolerance to surrounding disturbances, is evaluated. The
resulting accuracy and precision of glucose determination are 77 and 118mg/dl for 10-mm-sample-thickness, respectively. This
near-common-path configuration of the two-color pulse light provides good stability to fluctuations of sample temperature,
which is important in clinical applications. Considering the performance of femtosecond two-color pulse interferometry as
an optical glucose sensor, a suitable measurement site for in vivo optical glucose monitoring is discussed. 相似文献
22.
Theory and experiment of spatially and temporally partially coherent speckle shearing interferometry
The theory and experiment of spatially and temporally partially coherent speckle shearing interferometry is reported in this rapid communication for the first time. The general requirements for the surface roughness and coherence area of a diffuse object surface in spatially and temporally partially coherent speckle shearing interferometry are discussed. An experimental verification is presented and the results of theory and experiment are in good agreement. 相似文献
23.
正交变换在重积分中某些应用 总被引:2,自引:0,他引:2
姚云飞 《数学的实践与认识》2003,33(9):139-144
正交变换是代数学的基本内容 ,其用途十分广泛 .重积分的计算往往存在技术性的困难 ,若利用“正交变换”的有关理论去解决某些重积分的计算问题是颇有功效的 .本文将以“正交变换”为工具 ,简洁的处理重积分的某些问题 相似文献
24.
Hirofumi Tsumura. 《Mathematics of Computation》2004,73(245):251-258
In this paper, we give some evaluation formulas for Tornheim's type of alternating series by an elementary and combinatorial calculation of the uniformly convergent series. Indeed, we list several formulas for them by means of Riemann's zeta values at positive integers.
25.
In this paper, we investigate the exact distribution of the waiting time for ther-th ℓ-overlapping occurrence of success-runs of a specified length in a sequence of two state Markov dependent trials. The
probability generating functions are derived explicitly, and as asymptotic results, relationships of a negative binomial distribution
of orderk and an extended Poisson distribution of orderk are discussed. We provide further insights into the run-related problems from the viewpoint of the ℓ-overlapping enumeration
scheme. We also study the exact distribution of the number of ℓ-overlapping occurrences of success-runs in a fixed number
of trials and derive the probability generating functions. The present work extends several properties of distributions of
orderk and leads us a new type of geneses of the discrete distributions. 相似文献
26.
将介观无损耗传输线中的驻波场看成作相对运动的两列同频率的行波的叠加,此电路量子化后成为两个频率相同、不同模的光子场。计算和分析了激发相干态下电压和电流梯度的量子涨落,指出了双模传输线与一般的LC电路、双模传输线与单模传输线量子涨落的异同之处。 相似文献
27.
28.
G. Romero L. Alvarez E. Alanís L. Nallim R. Grossi 《Optics and Lasers in Engineering》2003,40(1-2):81-90
Real-time electronic speckle pattern interferometry (ESPI) was used for tuning and visualization of natural frequencies of a trapezoidal plate. The plate was excited to resonant vibration by a sinusoidal acoustical source, which provided a continuous range of audio frequencies. Fringe patterns produced during the time-average recording of the vibrating plate—corresponding to several resonant frequencies—were registered. From these interferograms, calculations of vibrational amplitudes by means of zero-order Bessel functions were performed in some particular cases. The system was also studied analytically. The analytical approach developed is based on the Rayleigh–Ritz method and on the use of non-orthogonal right triangular co-ordinates. The deflection of the plate is approximated by a set of beam characteristic orthogonal polynomials generated by using the Gram–Schmidt procedure. A high degree of correlation between computational analysis and experimental results was observed. 相似文献
29.
Yu-hai WU~ 《中国科学A辑(英文版)》2007,50(7):925-940
This paper concerns the number and distributions of limit cycles in a Z_2-equivariant quintic planar vector field.25 limit cycles are found in this special planar polynomial system and four different configurations of these limit cycles are also given by using the methods of the bifurcation theory and the qualitative analysis of the differential equation.It can be concluded that H(5)≥25=5~2, where H(5)is the Hilbert number for quintic polynomial systems.The results obtained are useful to study the weakened 16th Hilbert problem. 相似文献
30.
Electronic speckle interferometry (ESPI) is used to determine the Young's modulus E and Poisson ratio ν of an isotropic material. Micron scale deformations of the surface of the block of polymethyl-methacrylate (PMMA) are induced by normal application of a known near-point force. These deformations are recorded in speckle interferometric fringe patterns. An iterative minimum error inversion technique is developed to obtain the elastic properties from the positions of fringe peaks and troughs observed in the fringe patterns. Sensitivity tests of the method on calculated fringe patterns using measured experimental uncertainties suggest the technique will provide measures of the elastic moduli to better than 5%. In an experimental test on a bloc of PMMA (acrylic) the technique gave values of E and ν that differed from corresponding measures obtained using more conventional strain-gauge methods by less than 4%. 相似文献