全文获取类型
收费全文 | 6000篇 |
免费 | 606篇 |
国内免费 | 344篇 |
专业分类
化学 | 357篇 |
晶体学 | 9篇 |
力学 | 744篇 |
综合类 | 91篇 |
数学 | 4281篇 |
物理学 | 1468篇 |
出版年
2024年 | 7篇 |
2023年 | 49篇 |
2022年 | 84篇 |
2021年 | 84篇 |
2020年 | 166篇 |
2019年 | 159篇 |
2018年 | 151篇 |
2017年 | 176篇 |
2016年 | 185篇 |
2015年 | 131篇 |
2014年 | 289篇 |
2013年 | 723篇 |
2012年 | 246篇 |
2011年 | 323篇 |
2010年 | 272篇 |
2009年 | 355篇 |
2008年 | 361篇 |
2007年 | 405篇 |
2006年 | 320篇 |
2005年 | 294篇 |
2004年 | 265篇 |
2003年 | 258篇 |
2002年 | 219篇 |
2001年 | 192篇 |
2000年 | 202篇 |
1999年 | 185篇 |
1998年 | 154篇 |
1997年 | 98篇 |
1996年 | 108篇 |
1995年 | 64篇 |
1994年 | 67篇 |
1993年 | 44篇 |
1992年 | 55篇 |
1991年 | 53篇 |
1990年 | 29篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 15篇 |
1982年 | 10篇 |
1981年 | 15篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1974年 | 3篇 |
排序方式: 共有6950条查询结果,搜索用时 15 毫秒
961.
A dual-frequency Nd: YAG laser which can output two frequencies with frequency difference of more than 5 gigaherz is developed. By inserting and moving an intracavity quartz crystal wedge in diode pumped Nd:YAG laser, It can be obtained and tuned frequency difference in a wide frequency range. The stabilization of frequency difference in free state is much better than that of birefringent dual-frequency He-Ne lasers at similar laboratory conditions. With such a large tunable frequency difference i.e. short synthetic wavelength, the laser may be used as the light source of absolute distance interferometers. In our experiment, the methods for tuning frequency difference by rotating and applying a tunable force on the intracavity quartz plate are also studied. 相似文献
962.
It is shown that the multiplier norm of a shifted Jacobi multiplier sequence can be estimated by the (same) multiplier norm
of the original sequence uniformly with respect to the shift. Muckenhoupt’s transplantation theorem for Jacobi series is used
essentially, for which also a functional analytic understanding is given in terms of the minimality of the Jacobi system in
weighted L
p
-spaces.
相似文献
963.
Ozer TALO Feyzi BASAR 《数学学报(英文版)》2008,24(7):1205-1212
Recently, the space bvp of real or complex numbers consisting of all sequences whose differences are in the space lp has been studied by Basar, Altay [Ukrainian Math. J. 55(1)(2003), 136-147], where 1 ≤ p ≤ ∞. The main purpose of the present paper is to introduce the space bvp(F) of sequences of p-bounded variation of fuzzy numbers. Moreover, it is proved that the space bvp(F) includes the space lp(F) and also shown that the spaces bvp(F) and lp(F) axe isomorphic for 1 ≤ p ≤∞. Furthermore, some inclusion relations have been given. 相似文献
964.
刘卓军 《数学的实践与认识》2008,38(20)
实现和谐社会需要一个与之相适应的社会分配结构.借助基尼系数描述了一种和谐的社会分配结构.通过观察和分析我国近年的经济数据可以发现,为实现和谐的分配状态,我们必须应对许多严峻挑战:城乡差别依旧过大;接近占总人口20%的最贫困人群几乎没有财富积累;过大的地下经济扭曲并影响了社会的公平分配.进行社会分配必须兼顾均衡与效率.要实现和谐的分配状态,可以有许多考虑和选择.建议采取法律、法规、科技、政策和行政的各种手段,要坚决消灭近20%最贫困人群的入不敷出的情形;要全力打造中等收入阶层;要加大取缔黑色收入规范灰色收入的力度;要加快城镇化建设的步伐;要积极营建促进全民创业的环境. 相似文献
965.
In this article, a Timoshenko beam with tip body and boundary damping is considered. A linearized three-level difference scheme of the Timoshenko beam equations on uniform meshes is derived by the method of reduction of order. The unique solvability, unconditional stability and convergence of the difference scheme are proved. The convergence order in maximum norm is of order two in both space and time. A numerical example is presented to demonstrate the theoretical results. 相似文献
966.
Most of the literature on coded excitation describes the signal-to-noise ratio gain of a coded waveform in terms of the time-bandwidth product. We have shown that in the context of ultrasound imaging, the expression for the SNR gain provided by matched filtering a coded waveform, can be reduced to the total number of chips in the transmit signal. Hence, the SNR gain is independent of both the bandwidth and the duration of a single-chip. This concept is described in detail, clarifying this seeming contradiction. The impact of bandwidth and pulse duration on the SNR, SNR gain and axial resolution is described. Bandwidth requirements and the impact of regulatory peak-power limitations are also addressed. 相似文献
967.
Miloud Mihoubi 《Discrete Mathematics》2008,308(12):2450-2459
This paper concerns the study of the Bell polynomials and the binomial type sequences. We mainly establish some relations tied to these important concepts. Furthermore, these obtained results are exploited to deduce some interesting relations concerning the Bell polynomials which enable us to obtain some new identities for the Bell polynomials. Our results are illustrated by some comprehensive examples. 相似文献
968.
V. A. Dougalis F. Sturm G. E. Zouraris 《Mathematical Methods in the Applied Sciences》2009,32(12):1519-1540
We consider the third‐order Claerbout‐type wide‐angle parabolic equation (PE) of underwater acoustics in a cylindrically symmetric medium consisting of water over a soft bottom B of range‐dependent topography. There is strong indication that the initial‐boundary value problem for this equation with just a homogeneous Dirichlet boundary condition posed on B may not be well‐posed, for example when B is downsloping. We impose, in addition to the above, another homogeneous, second‐order boundary condition, derived by assuming that the standard (narrow‐angle) PE holds on B, and establish a priori H2 estimates for the solution of the resulting initial‐boundary value problem for any bottom topography. After a change of the depth variable that makes B horizontal, we discretize the transformed problem by a second‐order accurate finite difference scheme and show, in the case of upsloping and downsloping wedge‐type domains, that the new model gives stable and accurate results. We also present an alternative set of boundary conditions that make the problem exactly energy conserving; one of these conditions may be viewed as a generalization of the Abrahamsson–Kreiss boundary condition in the wide‐angle case. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
969.
Wolfe Duality for Interval-Valued Optimization 总被引:1,自引:0,他引:1
H. C. Wu 《Journal of Optimization Theory and Applications》2008,138(3):497-509
Weak and strong duality theorems in interval-valued optimization problem based on the formulation of the Wolfe primal and
dual problems are derived. The solution concepts of the primal and dual problems are based on the concept of nondominated
solution employed in vector optimization problems. The concepts of no duality gap in the weak and strong sense are also introduced,
and strong duality theorems in the weak and strong sense are then derived. 相似文献
970.
Jeffrey Goldstein 《Nonlinear dynamics, psychology, and life sciences》2001,5(3):197-204
This article examines recent attempts to gain insight into philosophical paradoxes through using NDS models employing iterated difference equations and resulting phase portraits and escape time diagrams. The temporal nature of such models is contrasted with an alternative approach based on the a-temporal and non-dynamical construct of a lattice. Finally, there is a discussion of how such strategies for understanding paradox transcend the realm of empirical research and enter territory in the philosophy of mathematics. 相似文献