全文获取类型
收费全文 | 7275篇 |
免费 | 1022篇 |
国内免费 | 634篇 |
专业分类
化学 | 1015篇 |
晶体学 | 91篇 |
力学 | 667篇 |
综合类 | 161篇 |
数学 | 5124篇 |
物理学 | 1873篇 |
出版年
2023年 | 66篇 |
2022年 | 94篇 |
2021年 | 130篇 |
2020年 | 184篇 |
2019年 | 218篇 |
2018年 | 193篇 |
2017年 | 243篇 |
2016年 | 285篇 |
2015年 | 208篇 |
2014年 | 371篇 |
2013年 | 628篇 |
2012年 | 369篇 |
2011年 | 456篇 |
2010年 | 400篇 |
2009年 | 447篇 |
2008年 | 497篇 |
2007年 | 505篇 |
2006年 | 424篇 |
2005年 | 386篇 |
2004年 | 332篇 |
2003年 | 284篇 |
2002年 | 329篇 |
2001年 | 271篇 |
2000年 | 261篇 |
1999年 | 231篇 |
1998年 | 191篇 |
1997年 | 183篇 |
1996年 | 129篇 |
1995年 | 84篇 |
1994年 | 69篇 |
1993年 | 51篇 |
1992年 | 42篇 |
1991年 | 47篇 |
1990年 | 27篇 |
1989年 | 32篇 |
1988年 | 30篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 17篇 |
1978年 | 13篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 4篇 |
排序方式: 共有8931条查询结果,搜索用时 265 毫秒
71.
讨论了微分方程组 dx/dt=-y(1 -ax2 n) +bx-cx2 n+ 1,dy/dt=x(1 -ax2 n) ,并且给出了其极限环存在唯一的条件 . 相似文献
72.
This paper proposes a floating-point genetic algorithm (FPGA) to solve the unit commitment problem (UCP). Based on the characteristics of typical load demand, a floating-point chromosome representation and an encoding–decoding scheme are designed to reduce the complexities in handling the minimum up/down time limits. Strategic parameters of the FPGA are characterized in detail, i.e., the evaluation function and its constraints, population size, operation styles of selection, crossover operation and probability, mutation operation and probability. A dynamic combination scheme of genetic operators is formulated to explore and exploit the FPGA in the non-convex solution space and multimodal objective function. Experiment results show that the FPGA is a more effective technique among the various styles of genetic algorithms, which can be applied to the practical scheduling tasks in utility power systems. 相似文献
73.
Rajesh Pereira 《Journal of Mathematical Analysis and Applications》2003,285(1):336-348
In 1959, Davis introduced the concept of a differentiator of an operator on a finite-dimensional Hilbert space. We prove that every such operator possesses a differentiator. We also use the theory of differentiators to solve several problems in the geometry of polynomials. For instance, we answer in the affirmative a twenty year old unsolved conjecture of Schoenberg, a related conjecture of Katsoprinakis and a fifty year old unsolved conjecture of De Bruijn and Springer. 相似文献
74.
仓库容量有限条件下的一类存贮管理模型 总被引:10,自引:1,他引:9
建立了一类仓库容量有限条件下存贮管理决策模型 ,给出最优存贮策略 . 相似文献
75.
In this paper, a successive supersymmetric rank‐1 decomposition of a real higher‐order supersymmetric tensor is considered. To obtain such a decomposition, we design a greedy method based on iteratively computing the best supersymmetric rank‐1 approximation of the residual tensors. We further show that a supersymmetric canonical decomposition could be obtained when the method is applied to an orthogonally diagonalizable supersymmetric tensor, and in particular, when the order is 2, this method generates the eigenvalue decomposition for symmetric matrices. Details of the algorithm designed and the numerical results are reported in this paper. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
76.
In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112-119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with the Hausdorff measure of noncompactness. 相似文献
77.
J. M. Kumpula J. Saramäki K. Kaski J. Kertész 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):41-45
According to Fortunato and Barthélemy, modularity-based community detection
algorithms have a resolution threshold such that small communities in a large
network are invisible. Here we generalize their work and show that the q-state
Potts community detection method introduced by Reichardt and Bornholdt
also has a resolution threshold. The model contains a parameter by which this threshold can be tuned, but no a priori principle
is known to select the proper value.
Single global optimization criteria do not seem capable for detecting all
communities if their size distribution is broad. 相似文献
78.
Jesús de la Cal Javier Cárcamo 《Journal of Mathematical Analysis and Applications》2007,334(2):1106-1115
As a consequence of Jensen's inequality, centered operators of probabilistic type (also called Bernstein-type operators) approximate convex functions from above. Starting from this fact, we consider several pairs of classical operators and determine, in each case, which one is better to approximate convex functions. In almost all the discussed examples, the conclusion follows from a simple argument concerning composition of operators. However, when comparing Szász-Mirakyan operators with Bernstein operators over the positive semi-axis, the result is derived from the convex ordering of the involved probability distributions. Analogous results for non-centered operators are also considered. 相似文献
79.
张国胜 《数学的实践与认识》2006,36(7):356-367
设W(1n)W2(n)…W(nn)是严平稳随即序列{Xn,n 1}的前几个变量的顺序统计量,Nn Mn是两正整值r.v,n 1.在较弱一些的混合条件下,本文给出了W(NMn)n标准化后的极限分布,从而使一些提法更趋一般化,主要结果推进了Rao(1984)和张国胜(1993)的工作.由于混合条件的减弱,使得对m-相关和正态平稳过程的具体应用讨论更加充分. 相似文献
80.
After more than 20 years of impressive development since the economic reforms in 1978, today western China is facing an increasing
development gap between its regions, particularly between urban and rural areas. Using the fuzzy comprehensive evaluation
model, this paper aims to demonstrate the evolution of the economic competitiveness levels base on two categories of geographical
unity in the province of Gansu located in Northwest China between 2000 and 2004. The results of fuzzy modeling are integrated
into GIS spatiotemporal analyses in order to identify the spatial variation of each significant change in terms of the regional
economic development. Our research effectively illustrates that there is a particular spatial dynamic of the economic development
from region to region. Although the cities have improved very well in their economic competitiveness, the rural areas and
minority regions still have a lot of progress to be achieved. 相似文献