首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   82980篇
  免费   6667篇
  国内免费   5033篇
化学   23660篇
晶体学   1769篇
力学   3608篇
综合类   439篇
数学   21988篇
物理学   43216篇
  2023年   260篇
  2022年   294篇
  2021年   394篇
  2020年   824篇
  2019年   1145篇
  2018年   1074篇
  2017年   770篇
  2016年   474篇
  2015年   411篇
  2014年   1090篇
  2013年   1937篇
  2012年   1181篇
  2011年   1865篇
  2010年   2517篇
  2009年   7122篇
  2008年   8213篇
  2007年   6591篇
  2006年   6058篇
  2005年   4137篇
  2004年   3862篇
  2003年   4125篇
  2002年   4853篇
  2001年   3782篇
  2000年   3563篇
  1999年   3388篇
  1998年   2812篇
  1997年   1965篇
  1996年   1744篇
  1995年   2231篇
  1994年   2170篇
  1993年   1618篇
  1992年   1125篇
  1991年   846篇
  1990年   688篇
  1989年   617篇
  1988年   573篇
  1987年   408篇
  1985年   958篇
  1984年   628篇
  1983年   489篇
  1982年   650篇
  1981年   796篇
  1980年   721篇
  1979年   559篇
  1978年   581篇
  1977年   539篇
  1976年   541篇
  1975年   320篇
  1974年   356篇
  1973年   463篇
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
1.
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.
4.
《Discrete Mathematics》2022,345(12):113083
Let G be a graph, ν(G) the order of G, κ(G) the connectivity of G and k a positive integer such that k(ν(G)?2)/2. Then G is said to be k-extendable if it has a matching of size k and every matching of size k extends to a perfect matching of G. A Hamiltonian path of a graph G is a spanning path of G. A bipartite graph G with vertex sets V1 and V2 is defined to be Hamiltonian-laceable if such that |V1|=|V2| and for every pair of vertices pV1 and qV2, there exists a Hamiltonian path in G with endpoints p and q, or |V1|=|V2|+1 and for every pair of vertices p,qV1,pq, there exists a Hamiltonian path in G with endpoints p and q. Let G be a bipartite graph with bipartition (X,Y). Define bn(G) to be a maximum integer such that 0bn(G)<min{|X|,|Y|} and (1) for each non-empty subset S of X, if |S||X|?bn(G), then |N(S)||S|+bn(G), and if |X|?bn(G)<|S||X|, then N(S)=Y; and (2) for each non-empty subset S of Y, if |S||Y|?bn(G), then |N(S)||S|+bn(G), and if |Y|?bn(G)<|S||Y|, then N(S)=X; and (3) bn(G)=0 if there is no non-negative integer satisfying (1) and (2).Let G be a bipartite graph with bipartition (X,Y) such that |X|=|Y| and bn(G)>0. In this paper, we show that if ν(G)2κ(G)+4bn(G)?4, then G is Hamiltonian-laceable; or if ν(G)>6bn(G)?2, then for every pair of vertices xX and yY, there is an (x,y)-path P in G with |V(P)|6bn(G)?2. We show some of its corollaries in k-extendable, bipartite graphs and a conjecture in k-extendable graphs.  相似文献   
5.
6.
7.
8.
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   
9.
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   
10.
针对二维球坐标系下中子输运方程的SN算法, 提出基于(单元, 方向)二元组的有向图模型, 在已有的基于有向图的并行流水线算法基础上, 设计粒度可控多级并行SN算法。其中, 采用区域分解和并行流水线相结合的方式挖掘空间-角度方向的并行度, 提出能群流水并行方法, 并通过设置合适的流水线粒度来平衡有向图调度、通信和空闲等待开销。实验结果表明: 该算法可以有效地求解二维球坐标系下的中子输运方程。在某国产并行机1920核上, 对于96万网格、60个方向、24能群、数十亿自由度的典型中子输运问题, 获得了71%的并行效率。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号