全文获取类型
收费全文 | 80520篇 |
免费 | 6577篇 |
国内免费 | 4919篇 |
专业分类
化学 | 24034篇 |
晶体学 | 1759篇 |
力学 | 3864篇 |
综合类 | 346篇 |
数学 | 18510篇 |
物理学 | 43503篇 |
出版年
2022年 | 222篇 |
2021年 | 344篇 |
2020年 | 700篇 |
2019年 | 987篇 |
2018年 | 916篇 |
2017年 | 676篇 |
2016年 | 469篇 |
2015年 | 409篇 |
2014年 | 1060篇 |
2013年 | 1710篇 |
2012年 | 1120篇 |
2011年 | 1736篇 |
2010年 | 2390篇 |
2009年 | 6831篇 |
2008年 | 7981篇 |
2007年 | 6458篇 |
2006年 | 5904篇 |
2005年 | 4014篇 |
2004年 | 3774篇 |
2003年 | 4057篇 |
2002年 | 4800篇 |
2001年 | 3730篇 |
2000年 | 3534篇 |
1999年 | 3354篇 |
1998年 | 2769篇 |
1997年 | 1935篇 |
1996年 | 1756篇 |
1995年 | 2232篇 |
1994年 | 2154篇 |
1993年 | 1614篇 |
1992年 | 1123篇 |
1991年 | 841篇 |
1990年 | 685篇 |
1989年 | 606篇 |
1988年 | 568篇 |
1987年 | 400篇 |
1986年 | 199篇 |
1985年 | 962篇 |
1984年 | 620篇 |
1983年 | 497篇 |
1982年 | 640篇 |
1981年 | 799篇 |
1980年 | 724篇 |
1979年 | 563篇 |
1978年 | 585篇 |
1977年 | 546篇 |
1976年 | 546篇 |
1975年 | 317篇 |
1974年 | 357篇 |
1973年 | 462篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Mohammed Harunor Rashid 《计算数学(英文版)》2022,40(1):44-69
In the present paper,we study the restricted inexact Newton-type method for solving the generalized equation 0∈f(x)+F(x),where X and Y are Banach spaces,f:X→Y is a Frechet differentiable function and F:X■Y is a set-valued mapping with closed graph.We establish the convergence criteria of the restricted inexact Newton-type method,which guarantees the existence of any sequence generated by this method and show this generated sequence is convergent linearly and quadratically according to the particular assumptions on the Frechet derivative of f.Indeed,we obtain semilocal and local convergence results of restricted inexact Newton-type method for solving the above generalized equation when the Frechet derivative of f is continuous and Lipschitz continuous as well as f+F is metrically regular.An application of this method to variational inequality is given.In addition,a numerical experiment is given which illustrates the theoretical result. 相似文献
2.
3.
本文研究了数值求解非自治随机微分方程的正则Euler-Maruyama分裂(CEMS)方法,该方程的漂移项系数带有刚性且允许超线性增长,扩散项系数满足全局Lipschitz条件.首先,证明了CEMS方法的强收敛性及收敛速度.其次,证明了在适当条件下CEMS方法是均方稳定的.进一步,利用离散半鞅收敛定理,研究了CEMS方法的几乎必然指数稳定性.结果表明,CEMS方法在漂移系数的刚性部分满足单边Lipschitz条件下可保持几乎必然指数稳定性.最后通过数值实验,检验了CEMS方法的有效性并证实了我们的理论结果. 相似文献
4.
A general framework for describing photofission observables of actinides at an average excitation energy below 30 MeV 下载免费PDF全文
Guan-Lin Wang Hao-Yang Lan Xiao-Ming Shi Zhi-Chao Zhu Wen Luo 《中国物理C(英文版)》2022,46(8):084102-084102-14
A reasonable prediction of photofission observables plays a paramount role in understanding the photofission process and guiding various photofission-induced applications, such as short-lived isotope production, nuclear waste disposal, and nuclear safeguards. However, the available experimental data for photofission observables are limited, and the existing models and programs have mainly been developed for neutron-induced fission processes. In this study, a general framework is proposed for characterizing the photofission observables of actinides, including the mass yield distributions (MYD) and isobaric charge distributions (ICD) of fission fragments and the multiplicity and energy distributions of prompt neutrons (np) and prompt γ rays (γp). The framework encompasses various systematic neutron models and empirical models considering the Bohr hypothesis and does not rely on the experimental data as input. These models are then validated individually against experimental data at an average excitation energy below 30 MeV, which shows the reliability and robustness of the general framework. Finally, we employ this framework to predict the characteristics of photofission fragments and the emissions of prompt particles for typical actinides including 232Th, 235, 238U and 240Pu. It is found that the 238U(γ, f) reaction is more suitable for producing neutron-rich nuclei compared to the 232Th(γ, f) reaction. In addition, the average multiplicity number of both np and γp increases with the average excitation energy. 相似文献
5.
Existence and Uniqueness of Solutions to Time-delays Stochastic Fractional Differential Equations with Non-Lipschitz Coefficients 下载免费PDF全文
In this paper, we consider the existence and uniqueness of solutions to time-varying delays stochastic fractional differential equations (SFDEs) with non-Lipschitz coefficients. By using fractional calculus and stochastic analysis, we can obtain the existence result of solutions for stochastic fractional differential equations. 相似文献
6.
Based on the primal mixed variational formulation, a stabilized nonconforming mixed finite element method is proposed for the linear elasticity on rectangular and cubic meshes. Two kinds of penalty terms are introduced in the stabilized mixed formulation, which are the jump penalty term for the displacement and the divergence penalty term for the stress. We use the classical nonconforming rectangular and cubic elements for the displacement and the discontinuous piecewise polynomial space for the stress, where the discrete space for stress are carefully chosen to guarantee the well-posedness of discrete formulation. The stabilized mixed method is locking-free. The optimal convergence order is derived in the $L^2$-norm for stress and in the broken $H^1$-norm and $L^2$-norm for displacement. A numerical test is carried out to verify the optimal convergence of the stabilized method. 相似文献
7.
Ram Manohar & Rajen Kumar Sinha 《计算数学(英文版)》2022,40(2):147-176
This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators. 相似文献
8.
针对大规模多输入多输出(multiple input multiple output, MIMO)系统信道估计中的导频设计问题,在压缩感知理论框架下,提出了一种基于信道重构错误率最小化的自适应自相关矩阵缩减参数导频优化算法.首先以信道重构错误率最小化为目标,推导了正交匹配追踪(orthogonal matching pursuit, OMP)算法下信道重构错误率与导频矩阵列相关性之间的关系,并得出优化导频矩阵的两点准则,即导频矩阵列相关性期望和方差最小化;然后研究了优化导频矩阵的方法,并提出相应的自适应自相关矩阵缩减参数导频矩阵优化算法,即在每次迭代过程中,以待优化矩阵平均列相关程度是否减小作为判断条件,调整自相关矩阵缩减参数值,使参数不断趋近于理论最优.仿真结果表明,与采用Gaussian矩阵、Elad方法、低幂平均列相关方法得到的导频矩阵相比,本文所提方法具有更好的列相关性,且具有更低的信道重构错误率. 相似文献
9.
In this paper we investigated the stability of fractional order fuzzy cellular neural networks with leakage delay and time varying delays. Based on Lyapunov theory and applying bounded techniques of fractional calculation, sufficient criterion are established to guarantee the stability. Hybrid feedback control is applied to derive the proposed results. Finally, numerical examples with simulation results are given to illustrate the effectiveness of the proposed method. 相似文献
10.
Liangliang Ma 《偏微分方程(英文版)》2021,34(2):144-169
This paper concerns about the regularity conditions of weak solutions to
the magnetic Bénard fluid system in $\mathbb{R}^3$. We show that a weak solution $(u,b,θ)(·,t)$ of
the 3D magnetic Bénard fluid system defined in $[0,T),$ which satisfies some regularity
requirement as $(u,b,θ),$ is regular in $\mathbb{R}^3×(0,T)$ and can be extended as a $C^∞$ solution
beyond $T$. 相似文献