全文获取类型
收费全文 | 739篇 |
免费 | 45篇 |
国内免费 | 52篇 |
专业分类
化学 | 228篇 |
力学 | 4篇 |
综合类 | 2篇 |
数学 | 71篇 |
物理学 | 77篇 |
综合类 | 454篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 42篇 |
2021年 | 65篇 |
2020年 | 21篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 22篇 |
2016年 | 19篇 |
2015年 | 28篇 |
2014年 | 57篇 |
2013年 | 41篇 |
2012年 | 42篇 |
2011年 | 30篇 |
2010年 | 32篇 |
2009年 | 34篇 |
2008年 | 34篇 |
2007年 | 37篇 |
2006年 | 35篇 |
2005年 | 30篇 |
2004年 | 26篇 |
2003年 | 38篇 |
2002年 | 25篇 |
2001年 | 12篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 10篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有836条查询结果,搜索用时 375 毫秒
751.
张林静 《山西师范大学学报:自然科学版》1998,12(2):68-70
以绥李三号、绫棱红、吉林六号为试材,对影响裂果的生理指标进行了测试,结果表明,果实硬度不均匀性促进果实开裂,水分影响裂果,而可溶性固性物含量与裂果无明显相关。在防止措施上,喷施硼砂溶液可减轻裂果比率。 相似文献
752.
杨宪泽 《西南民族学院学报(自然科学版)》1995,21(4):384-390
提出了一类问题的映射排序算法,其特点是附加一定的存储开销,在内排序中关键字与数组下标作映射或链接处理,不实施反复比较与交换关键字的操作,时间复杂性达到O(N),在外排序中,文件输入/输出次数减少,提高了效率,这类算法适宜今后的大规模信息处理中广泛采用。 相似文献
753.
将齿轮图的每个齿的顶端点与m个孤立点相连后所得的图称为n顶边星图,文[3]猜想,所有的n顶边星图都是优美图,本文证明了这一猜想是正确的. 相似文献
754.
755.
孙丽 《南阳理工学院学报》2009,1(2):16-19
吴为是张洁长篇小说《无字》中的女主角,在爱的追寻中迷失了方向,最终自杀。文章认为,导致吴为悲剧的原因集中于两点:一是男权意识在当代社会的延续和冥顽不化,二是女性对男权的认同和内化。真爱的追寻要有男人的自觉,更要有女人的自省。 相似文献
756.
Steven Orla Kimbrough Gary J. Koehler Ming Lu David Harlan Wood 《European Journal of Operational Research》2008
We explore data-driven methods for gaining insight into the dynamics of a two-population genetic algorithm (GA), which has been effective in tests on constrained optimization problems. We track and compare one population of feasible solutions and another population of infeasible solutions. Feasible solutions are selected and bred to improve their objective function values. Infeasible solutions are selected and bred to reduce their constraint violations. Interbreeding between populations is completely indirect, that is, only through their offspring that happen to migrate to the other population. We introduce an empirical measure of distance, and apply it between individuals and between population centroids to monitor the progress of evolution. We find that the centroids of the two populations approach each other and stabilize. This is a valuable characterization of convergence. We find the infeasible population influences, and sometimes dominates, the genetic material of the optimum solution. Since the infeasible population is not evaluated by the objective function, it is free to explore boundary regions, where the optimum is likely to be found. Roughly speaking, the No Free Lunch theorems for optimization show that all blackbox algorithms (such as Genetic Algorithms) have the same average performance over the set of all problems. As such, our algorithm would, on average, be no better than random search or any other blackbox search method. However, we provide two general theorems that give conditions that render null the No Free Lunch results for the constrained optimization problem class we study. The approach taken here thereby escapes the No Free Lunch implications, per se. 相似文献
757.
在总结回顾国内外地铁信号技术发展及技术特点的基础上,分析了我国地铁信号系统发展中存在的关键问题,提出了解决问题的方案与实施方法. 相似文献
758.
759.
760.
We propose and study the collective behavior of a model of networked signaling objects that incorporates several ingredients of real-life systems. These ingredients include spatial inhomogeneity with grouping of signaling objects, signal attenuation with distance, and delayed and impulsive coupling between non-identical signaling objects. Depending on the coupling strength and/or time-delay effect, the model exhibits completely, partially, and locally collective signaling behavior. In particular, a correlated signaling (CS) behavior is observed in which there exist time durations when nearly a constant fraction of oscillators in the system are in the signaling state. These time durations are much longer than the duration of a spike when a single oscillator signals, and they are separated by regular intervals in which nearly all oscillators are silent. Such CS behavior is similar to that observed in biological systems such as fireflies, cicadas, crickets, and frogs. The robustness of the CS behavior against noise is also studied. It is found that properly adjusting the coupling strength and noise level could enhance the correlated behavior. 相似文献