全文获取类型
收费全文 | 8991篇 |
免费 | 1220篇 |
国内免费 | 854篇 |
专业分类
化学 | 2338篇 |
晶体学 | 116篇 |
力学 | 1352篇 |
综合类 | 191篇 |
数学 | 3350篇 |
物理学 | 3718篇 |
出版年
2024年 | 19篇 |
2023年 | 95篇 |
2022年 | 227篇 |
2021年 | 250篇 |
2020年 | 278篇 |
2019年 | 230篇 |
2018年 | 250篇 |
2017年 | 330篇 |
2016年 | 372篇 |
2015年 | 307篇 |
2014年 | 478篇 |
2013年 | 745篇 |
2012年 | 468篇 |
2011年 | 543篇 |
2010年 | 473篇 |
2009年 | 570篇 |
2008年 | 592篇 |
2007年 | 553篇 |
2006年 | 553篇 |
2005年 | 474篇 |
2004年 | 388篇 |
2003年 | 382篇 |
2002年 | 309篇 |
2001年 | 289篇 |
2000年 | 264篇 |
1999年 | 220篇 |
1998年 | 194篇 |
1997年 | 181篇 |
1996年 | 171篇 |
1995年 | 158篇 |
1994年 | 95篇 |
1993年 | 87篇 |
1992年 | 73篇 |
1991年 | 56篇 |
1990年 | 55篇 |
1989年 | 60篇 |
1988年 | 50篇 |
1987年 | 29篇 |
1986年 | 22篇 |
1985年 | 38篇 |
1984年 | 36篇 |
1983年 | 9篇 |
1982年 | 24篇 |
1981年 | 17篇 |
1980年 | 4篇 |
1979年 | 15篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1973年 | 6篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
本文引进了广义极限鞅的概念,证明了 L~1有界的广义极限鞅 a.s.收敛于—可积随机变量。这样推广了通常极限鞅的相应收敛定理,并回答了 Stout 提出的问题:L~1有界的弱鞅在一定的条件下是 a.s.收敛的。 相似文献
32.
This research extends previous work with dynamic models to manage groundwater quality by using the consumptive nitrate use rate instead of the nitrate application rate. The analysis indicates that misspecification results in overestimation of economic benefits, and supra-optimum nitrogen fertilizer application rates and groundwater nitrate stocks at a steady state. 相似文献
33.
34.
In this paper, we provide numerical means to compute the quasi-stationary (QS) distributions inM/GI/1/K queues with state-dependent arrivals andGI/M/1/K queues with state-dependent services. These queues are described as finite quasi-birth-death processes by approximating the general distributions in terms of phase-type distributions. Then, we reduce the problem of obtaining the QS distribution to determining the Perron-Frobenius eigenvalue of some Hessenberg matrix. Based on these arguments, we develop a numerical algorithm to compute the QS distributions. The doubly-limiting conditional distribution is also obtained by following this approach. Since the results obtained are free of phase-type representations, they are applicable for general distributions. Finally, numerical examples are given to demonstrate the power of our method. 相似文献
35.
认为物质的质量(能量)存在形式可分为两部分,一部分是以纯物质形式存在的,另一部分是以纯重力场形式存在的.物质质量(能量)这两种形式各自对应着相应的能量 动量张量,物质总的能量-动量张量可表示为Tμν=T(Ⅰ)μν+T(Ⅱ)μν,这里,T(Ⅰ)μν,T(Ⅱ)μν分别代表物质纯物质部分和纯重力场部分的能量-动量张量.通过类比电磁理论,定义:ωμ≡-c2gμ0/g00,并引入一个反对称张量Dμν=ωμ/xν-ων/xμ,则物质纯重力场部分的能量-动量张量为T(Ⅱ)μν=(DμρDρν-gμνDαβDαβ/4
关键词:
能量-动量张量
纯重力场
重力场方程
标量重力势
矢量重力势 相似文献
36.
In this note, we study convergence rates in the law of large numbers for independent and identically distributed random variables under sublinear expectations. We obtain a strong L^p-convergence version and a strongly quasi sure convergence version of the law of large numbers. 相似文献
37.
Mixed and hybrid finite element methods for the resolution of a wide range of linear and nonlinear boundary value problems (linear elasticity, Stokes problem, Navier–Stokes equations, Boussinesq equations, etc.) have known a great development in the last few years. These methods allow simultaneous computation of the original variable and its gradient, both of them being equally accurate. Moreover, they have local conservation properties (conservation of the mass and the momentum) as in the finite volume methods.The purpose of this paper is to give a review on some mixed finite elements developed recently for the resolution of Stokes and Navier–Stokes equations, and the linear elasticity problem. Further developments for a quasi-Newtonian flow obeying the power law are presented. 相似文献
38.
建立一个描述低能电子在多元多层介质中散射的物理模型,运用MonteCarlo方法模拟低能电子在靶体胶衬底中的复杂散射过程,在此基础上通过大量计算研究入射束能、胶层厚度、衬底材料等不同曝光条件对抗蚀剂沉积能密度分布的影响,获得沉积能分布规律:适量的低束能、薄胶层、低原子序数衬底可以使前散射电子对胶中沉积能密度分布的贡献增大、背散射电子的贡献减小,从而提高曝光分辨率.
关键词:
电子束曝光
MonteCarlo方法
低能电子散射
能量沉积 相似文献
39.
可提前还款的定期贷款是隐含着期权的利率衍生物,本文建立CIR利率模型下可提前还款的定期贷款的数学模型,通过离散偏微分方程,建立了模型的计算方法,讨论了随机利率对提前还贷的影响. 相似文献
40.
Temperature effects on deposition rate of silicon nitride films were characterized by building a neural network prediction model. The silicon nitride films were deposited by using a plasma enhanced chemical vapor deposition system and process parameter effects were systematically characterized by 26−1 fractional factorial experiment. The process parameters involved include a radio frequency power, pressure, temperature, SiH4, N2, and NH3 flow rates. The prediction performance of generalized regression neural network was drastically improved by optimizing multi-valued training factors using a genetic algorithm. Several 3D plots were generated to investigate parameter effects at various temperatures. Predicted variations were experimentally validated. The temperature effect on the deposition rate was a complex function of parameters but N2 flow rate. Larger decreases in the deposition rate with the temperature were only noticed at lower SiH4 (or higher NH3) flow rates. Typical effects of SiH4 or NH3 flow rate were only observed at higher or lower temperatures. A comparison with the refractive index model facilitated a selective choice of either SiH4 or NH3 for process optimization. 相似文献