全文获取类型
收费全文 | 2998篇 |
免费 | 445篇 |
国内免费 | 141篇 |
专业分类
化学 | 323篇 |
晶体学 | 5篇 |
力学 | 596篇 |
综合类 | 82篇 |
数学 | 1615篇 |
物理学 | 963篇 |
出版年
2024年 | 5篇 |
2023年 | 28篇 |
2022年 | 65篇 |
2021年 | 78篇 |
2020年 | 99篇 |
2019年 | 90篇 |
2018年 | 89篇 |
2017年 | 96篇 |
2016年 | 131篇 |
2015年 | 96篇 |
2014年 | 173篇 |
2013年 | 203篇 |
2012年 | 152篇 |
2011年 | 207篇 |
2010年 | 158篇 |
2009年 | 160篇 |
2008年 | 170篇 |
2007年 | 162篇 |
2006年 | 179篇 |
2005年 | 183篇 |
2004年 | 154篇 |
2003年 | 123篇 |
2002年 | 123篇 |
2001年 | 80篇 |
2000年 | 89篇 |
1999年 | 65篇 |
1998年 | 66篇 |
1997年 | 51篇 |
1996年 | 51篇 |
1995年 | 45篇 |
1994年 | 41篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1959年 | 3篇 |
1957年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有3584条查询结果,搜索用时 15 毫秒
11.
The transport of monodisperse as well as polydisperse colloid suspensions in a two-dimensional, water saturated fracture with spatially variable and anisotropic aperture is investigated with a particle tracking model. Both neutrally buoyant and dense colloid suspensions are considered. Although flow and transport in fractured subsurface formations have been studied extensively by numerous investigators, the transport of dense, polydisperse colloid suspensions in a fracture with spatially variable and anisotropic aperture has not been previously explored. Simulated snapshots and breakthrough curves of ensemble averages of several realizations of a log-normally distributed aperture field show that polydisperse colloids exhibit greater spreading than monodisperse colloids, and dense colloids show greater retardation than neutrally buoyant colloids. Moreover, it is demonstrated that aperture anisotropy oriented along the flow direction substantially increases colloid spreading; whereas, aperture anisotropy oriented transverse to the flow direction retards colloid movement. 相似文献
12.
讨论了顾客到达时间和服务时间与等待队列队长有关的排队系统模拟,顾客服务次数不止1次即出现循环的复杂排队系统,引入到达因子、服务台因子和循环因子,在串并联多服务台情形下建立了4类计算机模拟模型,给出该复杂循环排队系统在进程调度中的应用并进行了计算机模拟. 相似文献
13.
风力发电机组变速恒频控制系统研究 总被引:2,自引:0,他引:2
全面介绍了一种最新应用于风力发电中的新型电机—无刷双馈电机,并分析了这种新型电机作变速恒频运行的原理并对这种电机进行了动态特性仿真研究,给出了形式简洁的控制方程和易于实现的控制方案。 相似文献
14.
Lahcne Mezrag 《Mathematische Nachrichten》2004,266(1):60-67
In [5], it is proved that a bounded linear operator u, from a Banach space Y into an Lp(S, ν) factors through Lp1 (S, ν) for some p1 > 1, if Y* is of finite cotype; (S, ν) is a probability space for p = 0, and any measure space for 0 < p < 1. In this paper, we generalize this result to uv, where u : Y → Lp(S, ν) and v : X → Y are linear operators such that v* is of finite Ka?in cotype. This result gives also a new proof of Grothendieck's theorem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
15.
Considerthediferenceequationwithavariabledelayxn-xn-1=F(xn,xr(n),n=n0,n0+1,…(1)where(H1):F∈C(R×R,R),F(u,v)isdecreasingwithres... 相似文献
16.
This paper proposes a model for the parametric representation of linguistic hedges in Zadeh’s fuzzy logic. In this model each linguistic truth-value, which is generated from a primary term of the linguistic truth variable, is identified by a real number r depending on the primary term. It is shown that the model yields a method of efficiently computing linguistic truth expressions accompanied with a rich algebraic structure of the linguistic truth domain, namely De Morgan algebra. Also, a fuzzy logic based on the parametric representation of linguistic truth-values is introduced. 相似文献
17.
The possibilities of controlling the laser beam properties by a deformable mirror introduced into the laser optical cavity
were studied theoretically and experimentally. The experiments were performed under conditions of an industrial high power
transverse flow cw CO2 laser operating with a stable resonator of a folded configuration. A deformable bimorph mirror of a surface profile controlled
by the voltage applied to the mirror electrodes is implemented to the laser system as a back cavity mirror or as a one of
the inner folding mirrors. The near-and far-field characteristics of the laser beam versus the resonator configuration controlled
by the changes of the focal length of the deformable mirror are discussed in the paper. The analysis reveals that the resonator
with an inner deformable mirror is much more sensitive to the mirror curvature variations than the resonator in which the
deformable mirror is used as a back cavity mirror. The presented results show that dynamic and controllable changes in the
resonator properties result in the controlled modification and optimisation of the laser output power and spatial parameters
of the laser radiation. 相似文献
18.
对于任意秩有限总体,在二次损失下,有关文献已给出了线性可预测变量在齐次线性预测类中的唯一线性Minimax预测.本文在正态假设下,证明了这个线性Minimax预测也是线性可预测变量在一切预测类中的唯一Minimax预测. 相似文献
19.
本文提出等效远场的可变孔径方法,由测量光纤远场累积分布求得模场半径。并且利用Petermann关于模场半径的新定义,推出了一种对非高斯模场分布也适用的求模场半径的方法。实验表明,这种测量方法简便可靠,在不同的制备端面下,重复测量的标准误差小于0.04μm。 相似文献
20.
In this paper, the possibility of using the gradients of the temperature and of the internal parameters as additional state variables in Continuum Thermodynamics is considered. The expressions of the two principles are discussed and Clausius–Duhem inequality is derived under an appropriate statement of the internal entropy production. Several formulations are proposed and compared to existing results in the literature. To cite this article: P. Ireman, Q.S. Nguyen, C. R. Mecanique 332 (2004). 相似文献