全文获取类型
收费全文 | 5454篇 |
免费 | 627篇 |
国内免费 | 431篇 |
专业分类
化学 | 378篇 |
晶体学 | 3篇 |
力学 | 494篇 |
综合类 | 234篇 |
数学 | 4424篇 |
物理学 | 979篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 94篇 |
2021年 | 141篇 |
2020年 | 112篇 |
2019年 | 87篇 |
2018年 | 93篇 |
2017年 | 172篇 |
2016年 | 242篇 |
2015年 | 139篇 |
2014年 | 300篇 |
2013年 | 338篇 |
2012年 | 308篇 |
2011年 | 342篇 |
2010年 | 306篇 |
2009年 | 378篇 |
2008年 | 348篇 |
2007年 | 387篇 |
2006年 | 352篇 |
2005年 | 317篇 |
2004年 | 250篇 |
2003年 | 265篇 |
2002年 | 206篇 |
2001年 | 169篇 |
2000年 | 150篇 |
1999年 | 132篇 |
1998年 | 160篇 |
1997年 | 109篇 |
1996年 | 91篇 |
1995年 | 64篇 |
1994年 | 54篇 |
1993年 | 48篇 |
1992年 | 55篇 |
1991年 | 31篇 |
1990年 | 18篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 7篇 |
1986年 | 16篇 |
1985年 | 38篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有6512条查询结果,搜索用时 15 毫秒
51.
52.
对数似然比与整值随机变量序列的一类强律 总被引:2,自引:0,他引:2
本文引进对数似然比作为整值随机变量序列相对于服从几何分布的独立随机变量序列的偏差的一种度量,并通过限制对数似然比给出了样本空间的一个子集.在此子集上得到了一类用不等式表示的强律,其中包含整值随机变量序列与相对熵密度及几何分布的熵函数有关的若干极限性质. 相似文献
53.
本文针对单件小批量生产系统 ,建立了模糊优化的动态随机投入产出模型 ,同时给出了该模型的递推解法 ,并用此模型对某单件小批企业在生产计划期的商品量进行了规划 相似文献
54.
Electric fields of the anions, cations and neutral forms of 2-aminopurine and 6-thioguanine have been mapped. Certain important
features of the maps are similar to those found earlier in the neutral and ionic forms of adenine and guanine. The computed
electric field patterns satisfactorily explain reactive sites and biological activity of the molecules. 相似文献
55.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献
56.
Gisella Facchinetti 《Fuzzy Optimization and Decision Making》2002,1(3):313-327
In this paper we present two definitions of possibilistic weighted average of fuzzy numbers, and by them we introduce two different rankings on the set of real fuzzy numbers. The two methods are dependent on several parameters. In the first case, the parameter is constant and the results generalize what Carlsson and Fuller have obtained in (2001). In the second case, the parameter is a function, not fixed a priori by the decision maker, but it depends on the position of the interval on the real axe. In all the two cases we call the parameter degree of risk, which takes into account of a risk-tendency or aversion of the decision maker. 相似文献
57.
Optimization theory provides a framework for determining the best decisions or actions with respect to some mathematical model of a process. This paper focuses on learning to act in a near-optimal manner through reinforcement learning for problems that either have no model or the model is too complex. One approach to solving this class of problems is via approximate dynamic programming. The application of these methods are established primarily for the case of discrete state and action spaces. In this paper we develop efficient methods of learning which act in complex systems with continuous state and action spaces. Monte-Carlo approaches are employed to estimate function values in an iterative, incremental procedure. Derivative-free line search methods are used to obtain a near-optimal action in the continuous action space for a discrete subset of the state space. This near-optimal control policy is then extended to the entire continuous state space via a fuzzy additive model. To compensate for approximation errors, a modified procedure for perturbing the generated control policy is developed. Convergence results under moderate assumptions and stopping criteria are established. 相似文献
58.
提出并使用如下广义复合隐迭代格式逼近非扩张映像族{Ti}Ni=1公共不动点:{xn=αnxn-1 (1-αn)Tnyn,yn=rnxn snxn-1 tnTnxn wnTnxn-1,rn sn tn wn=1,{αn},{rn},{sn},{tn},{wn}∈[0,1],这里Tn=TnmodN.该文提出的广义复合隐迭代格式包含了目前多种迭代格式,因此,所得强弱收敛定理推广及发展了Mann,Ishikawa,XuandOri,等许多作者的结果. 相似文献
59.
Attapol Kaewkhao 《Journal of Mathematical Analysis and Applications》2007,333(2):950-958
We give some sufficient conditions for the Domínguez-Lorenzo condition in terms of the James constant, the Jordan-von Neumann constant, and the coefficient of weak orthogonality. As a consequence, we obtain fixed point theorems for multivalued nonexpansive mappings. 相似文献
60.