全文获取类型
收费全文 | 10225篇 |
免费 | 839篇 |
国内免费 | 858篇 |
专业分类
化学 | 804篇 |
晶体学 | 14篇 |
力学 | 624篇 |
综合类 | 252篇 |
数学 | 8762篇 |
物理学 | 1466篇 |
出版年
2024年 | 7篇 |
2023年 | 97篇 |
2022年 | 122篇 |
2021年 | 180篇 |
2020年 | 245篇 |
2019年 | 274篇 |
2018年 | 247篇 |
2017年 | 316篇 |
2016年 | 317篇 |
2015年 | 198篇 |
2014年 | 440篇 |
2013年 | 779篇 |
2012年 | 534篇 |
2011年 | 533篇 |
2010年 | 456篇 |
2009年 | 660篇 |
2008年 | 627篇 |
2007年 | 640篇 |
2006年 | 548篇 |
2005年 | 490篇 |
2004年 | 443篇 |
2003年 | 407篇 |
2002年 | 422篇 |
2001年 | 389篇 |
2000年 | 343篇 |
1999年 | 310篇 |
1998年 | 277篇 |
1997年 | 273篇 |
1996年 | 216篇 |
1995年 | 165篇 |
1994年 | 142篇 |
1993年 | 107篇 |
1992年 | 78篇 |
1991年 | 74篇 |
1990年 | 78篇 |
1989年 | 53篇 |
1988年 | 38篇 |
1987年 | 41篇 |
1986年 | 37篇 |
1985年 | 47篇 |
1984年 | 40篇 |
1983年 | 23篇 |
1982年 | 42篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 28篇 |
1978年 | 28篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
82.
The theory of monotone semiflows has been widely applied to functional differential equations (FDEs). The studies on the theory and applications of monotone semiflows for FDEs are very important and interesting. A brief des-cription of our recent works are as follows.By using general monotone semiflow theory, several results of positively invariant sets, monotone solutions and contracting rectangles of retarded functional differential equations(RFDEs) with infinite delay are gained under the assumption of quasimonotonicity; sufficient conditions for the existence, un-iqueness and global attractivity of periodic solutions are also established by combining the theory of monotone semiflows for neutral functional differential equations(NFDEs) and Krasnoselskii's fixed point theorem. 相似文献
83.
This paper presents a new generic Evolutionary Algorithm (EA) for retarding the unwanted effects of premature convergence. This is accomplished by a combination of interacting generic methods. These generalizations of a Genetic Algorithm (GA) are inspired by population genetics and take advantage of the interactions between genetic drift and migration. In this regard a new selection scheme is introduced, which is designed to directedly control genetic drift within the population by advantageous self-adaptive selection pressure steering. Additionally this new selection model enables a quite intuitive heuristics to detect premature convergence. Based upon this newly postulated basic principle the new selection mechanism is combined with the already proposed Segregative Genetic Algorithm (SEGA), an advanced Genetic Algorithm (GA) that introduces parallelism mainly to improve global solution quality. As a whole, a new generic evolutionary algorithm (SASEGASA) is introduced. The performance of the algorithm is evaluated on a set of characteristic benchmark problems. Computational results show that the new method is capable of producing highest quality solutions without any problem-specific additions. 相似文献
84.
设{Xni:1≤i≤n,n≥1}为行间独立的B值r.v.阵列,g(z)是指数为1/p的正则变化函数,r>0,{ani 1≤t≤n,n≥1}为实数阵列,本文得到了使(?)成立的条件,推广并改进了Stout及Sung等的著名结论. 相似文献
85.
将心磁信号从干扰噪声中加以提取并有效地消除噪声干扰是心磁信号处理中尤为重要的环节 .从改进算法的角度出发,提出互补型自适应滤波器结构以实现心磁信号的消噪处理.该滤波器针对心磁这类非平稳信号进行设计,有效地解决了常规自适应滤波器应用于心磁信号处理时收敛速度和稳态误差的矛盾.通过仿真实验和心磁实验结果表明,该算法能有效地消除心磁信号的背景噪声和工频干扰噪声.同时该算法也可用于其他非平稳信号的消噪处理.
关键词:
自适应滤波
心磁图
最小均方误差 相似文献
86.
Manuel Ritoré Cé sar Rosales 《Transactions of the American Mathematical Society》2004,356(11):4601-4622
We study the problem of existence of regions separating a given amount of volume with the least possible perimeter inside a Euclidean cone. Our main result shows that nonexistence for a given volume implies that the isoperimetric profile of the cone coincides with the one of the half-space. This allows us to give some criteria ensuring existence of isoperimetric regions: for instance, local convexity of the cone at some boundary point.
We also characterize which are the stable regions in a convex cone, i.e., second order minima of perimeter under a volume constraint. From this it follows that the isoperimetric regions in a convex cone are the euclidean balls centered at the vertex intersected with the cone.
87.
Summary Our purpose is to extend results due to P. Chandra and L. Leindler concerning the order of approximation by means of Fourier series for functions belonging to generalized Lipschitz-classes. 相似文献
88.
增长曲线模型中回归系数的广义根方估计 总被引:6,自引:0,他引:6
本文对增长曲线模型中的回归系数B提出了一种新的估计形式-广义根方估计的B(K),其中K=diag(k1,k2,…,kp)并证明了通过广义根方偏参数ki(i=1,2,…,p)的适当选取可使得该估计在均方误差矩阵的意义下优于已有的LS估计和根方估计,及广义根方估计是可容许估计,本文还给出了选取广义根方偏参数的两种方法,算法及一个应用实例。 相似文献
89.
加速牛顿迭代收敛的新方法 总被引:2,自引:0,他引:2
提出了加速牛顿迭代收敛的新思想,构造出一类加权牛顿迭代格式,通过选取最优加权因子,使得该格式具有高阶收敛性和较小的渐近误差常数。 相似文献
90.
This work is devoted to near-optimal controls of large-scale discrete-time nonlinear dynamic systems driven by Markov chains; the underlying problem is to minimize an expected cost function. Our main goal is to reduce the complexity of the underlying systems. To achieve this goal, discrete-time control models under singularly-perturbed Markov chains are introduced. Using a relaxed control representation, our effort is devoted to finding near-optimal controls. Lumping the states in each irreducible class into a single state gives rise to a limit system. Applying near-optimal controls of the limit system to the original system, near-optimal controls of the original system are derived. 相似文献