全文获取类型
收费全文 | 13647篇 |
免费 | 1689篇 |
国内免费 | 394篇 |
专业分类
化学 | 1477篇 |
晶体学 | 30篇 |
力学 | 1646篇 |
综合类 | 191篇 |
数学 | 8972篇 |
物理学 | 3414篇 |
出版年
2024年 | 20篇 |
2023年 | 126篇 |
2022年 | 309篇 |
2021年 | 413篇 |
2020年 | 263篇 |
2019年 | 263篇 |
2018年 | 284篇 |
2017年 | 390篇 |
2016年 | 396篇 |
2015年 | 297篇 |
2014年 | 602篇 |
2013年 | 770篇 |
2012年 | 817篇 |
2011年 | 683篇 |
2010年 | 685篇 |
2009年 | 832篇 |
2008年 | 892篇 |
2007年 | 952篇 |
2006年 | 804篇 |
2005年 | 680篇 |
2004年 | 512篇 |
2003年 | 528篇 |
2002年 | 479篇 |
2001年 | 454篇 |
2000年 | 403篇 |
1999年 | 322篇 |
1998年 | 345篇 |
1997年 | 309篇 |
1996年 | 221篇 |
1995年 | 232篇 |
1994年 | 196篇 |
1993年 | 172篇 |
1992年 | 156篇 |
1991年 | 127篇 |
1990年 | 106篇 |
1989年 | 85篇 |
1988年 | 74篇 |
1987年 | 63篇 |
1986年 | 62篇 |
1985年 | 78篇 |
1984年 | 64篇 |
1983年 | 22篇 |
1982年 | 36篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 37篇 |
1978年 | 28篇 |
1977年 | 34篇 |
1976年 | 22篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
利用密度泛函理论研究了Al12N和Al12B团簇的原子结构和电子性质,通过各种异构体的比较,发现两种掺杂团簇的最低能量结构都是完好的二十面体(Ih)结构,N(B)原子占据在二十面体的中心.高对称性团簇形成稀疏离散的电子态密度和大的电子能隙.在Al-N之间发生较大的电荷转移.因此我们建议把Al12N团簇看作是碱金属超原子,Al12B团簇看作是卤素超原子,用来构造团簇组装固体. 相似文献
182.
“Optimization of aircraft maintenance/support infrastructure using genetic algorithms—level of repair analysis” 总被引:4,自引:0,他引:4
Level of repair analysis (LORA) is an approach used during the design stage of complex equipment for analysis of the cost
effectiveness of competing maintenance strategies. LORA is carried as a part of the life cycle cost and cost of ownership
analysis and plays a significant role in minimizing the life cycle cost and cost of ownership of the capital equipment. Since
many purchasing decisions of complex equipment are based on cost of ownership, it has become essential to carry out LORA to
compete in the market. In this paper, we develop a mathematical model for LORA and propose a solution methodology based on
genetic algorithms. The concept is illustrated using a hypothetical aircraft engine. 相似文献
183.
Some effective methods for unconstrained optimization based on the solution of systems of ordinary differential equations 总被引:5,自引:0,他引:5
A. A. Brown M. C. Bartholomew-Biggs 《Journal of Optimization Theory and Applications》1989,62(2):211-224
In this paper, we review briefly some methods for minimizing a functionF(x), which proceed by follwoing the solution curve of a system of ordinary differential equations. Such methods have often been thought to be unacceptably expensive; but we show, by means of extensive numerical tests, using a variety of algorithms, that the ODE approach can in fact be implemented in such a way as to be more than competitive with currently available conventional techniques.This work was supported by a SERC research studentship for the first author. Both authors are indebted to Dr. J. J. McKeown and Dr. K. D. Patel of SCICON Ltd, the collaborating establishment, for their advice and encouragement. 相似文献
184.
给出了大规模界约束优化的一个子空间截断牛顿法。利用截断牛顿法修正非有效约束所对应的变量,用投影梯度法修正有效约束所对应的变量,文中证明了方法的整体收敛性,并对方法进行了数值试验,且与子空间有限内存拟牛顿法进行了数值比较。 相似文献
185.
We introduce an interesting hierarchy of rational order chaotic maps that possess an invariant measure. In contrast to the
previously introduced hierarchy of chaotic maps [1–5], with merely entropy production, the rational order chaotic maps can
simultaneously produce and consume entropy. We compute the Kolmogorov-Sinai entropy of these maps analytically and also their
Lyapunov exponent numerically, where the obtained numerical results support the analytical calculations. 相似文献
186.
在本文中,我们提出了双凹规划问题和更一般的广义凹规划问题。我们给出了双凹规划问题的整体最优性条件,并构造了一个有限终止外逼近算法。 相似文献
187.
We study infinite-dimensional systems of ordinary differential equations having applications in some popular and important physical problems. The appearance of infinite-dimensional space–time chaos is considered, namely, the bifurcations and critical phenomena that occur in the phase space of the systems and explain some physical problems are described. 相似文献
188.
In a recent paper [17] we proposed a stochastic algorithm which generates optimal probabilities for the decompression of
an image represented by the fixed point of an IFS system (SAOP). We show here that such an algorithm is in fact a non trivial
example of Generalized Random System with Complete Connections. We also exhibit a generalization which could represent the
solution to the inverse problem for an image with grey levels, if a fixed set of contraction maps is available.
Received: 1 July 2002 相似文献
189.
箱覆盖问题是NP困难问题中的经典问题,得到了广泛地研究,九十年代以来,半定松驰策略被用来求解组合优化问题,取得了很好的结果[13],本文首次给箱覆盖问题的半定松驰算法,算法的理论分析结果表明它适合于求解大规模的箱覆盖问题。 相似文献
190.