首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4918篇
  免费   210篇
  国内免费   578篇
系统科学   835篇
丛书文集   124篇
教育与普及   19篇
理论与方法论   10篇
现状及发展   73篇
综合类   4645篇
  2024年   29篇
  2023年   43篇
  2022年   67篇
  2021年   70篇
  2020年   82篇
  2019年   58篇
  2018年   61篇
  2017年   94篇
  2016年   96篇
  2015年   151篇
  2014年   230篇
  2013年   227篇
  2012年   325篇
  2011年   354篇
  2010年   279篇
  2009年   349篇
  2008年   350篇
  2007年   399篇
  2006年   334篇
  2005年   307篇
  2004年   244篇
  2003年   205篇
  2002年   173篇
  2001年   169篇
  2000年   146篇
  1999年   152篇
  1998年   143篇
  1997年   128篇
  1996年   130篇
  1995年   101篇
  1994年   63篇
  1993年   51篇
  1992年   30篇
  1991年   15篇
  1990年   19篇
  1989年   13篇
  1988年   7篇
  1987年   6篇
  1986年   2篇
  1981年   1篇
  1955年   3篇
排序方式: 共有5706条查询结果,搜索用时 578 毫秒
21.
代码传输是实现无线传感器网络应用重构的关键技术.首先研究传感器网络环境自适应应用重构(EAAR)模型的两种代码传输模式-拉模式和推模式,并结合两种模式的特点提出一种适用于分簇传感器网络的能量有效代码传输模式-基于簇的混合代码传输(Cluster-based Hybrid Code Transmission, CHCT).在该模式下,簇头节点采用拉方式从基站获取代码,簇内节点采用推方式进行代码传输.仿真实验验证了方法的有效性并讨论了影响CHCT性能的主要参数.  相似文献   
22.
Sensor networks consisted of low-cost, low-power, multifunctional miniature sensor devices have played an important role in our daily life. Light and humidity monitoring, seismic and animal activity detection, environment and habitat monitoring are the most common applications. However, due to the limited power supply, ordinary query methods and algorithms can not be applied on sensor networks. Queries over sensor networks should be power-aware to guarantee the maximum power savings. The minimal power consumption by avoiding the expensive communication of the redundant sensor nodes is concentrated on. A lot of work have been done to reduce the participated nodes, but none of them have considered the overlapping minimum bounded rectangle (MBR) of sensors which make them impossible to reach the optimization solution. The proposed OMSI-tree and OMR algorithm can efficiently solve this problem by executing a given query only on the sensors involved. Experiments show that there is an obvious improvement compared with TinyDB and other spatial index, adopting the proposed schema and algorithm.  相似文献   
23.
The participation of non-state actors in implementation processes is often understood as a means to increase compliance efficiency. But the implementation of spatial policies frequently focuses on pre-established goals, processes and instruments and thus renders difficult open discourse and shared decision-making. This paper introduces conflict pattern analysis (CPA) as a tool that supports the analysis of the actual actor constellation in order to define efficient approaches that avoid common problems of participatory processes. CPA is a semi-formalised method that helps to identify key-actors, their relations and interaction amongst each other as well as their core beliefs, interests and resources. It aggregates this information to interaction patterns that can be compared, classified and linked to different participatory methods on a theoretically informed basis. Particularly on the local and regional level, this could be the first step for successful (participatory) implementation strategies.  相似文献   
24.
信托制度最根本的特点是“所有权和利益相分离”。信托财产的独立性使商事信托成为其他法律制度如代理或合同所不能替代的法律制度。从效率的角度出发,证明信托制度的科学性和实用性及其法理价值,并对构建独持养老金制度和集合投资信托制度的商事设计进行探讨。  相似文献   
25.
An artificial neural network (ANN) is applied in the preliminary structural design of reticulated shells. Major efforts are made to enhance the generalization ability of networks through well-selected training samples. Number-theoretic methods (NTMs) are adopted to generate samples with low discrepancy, i.e.uniformly scattered in the domain, where discrepancy is a quantitative measurement of the uniformity. The discrepancy of the NTM-based sample set is 1/6-1/7 that of samples with equal spacing. In a case study,networks trained by NTM-based samples are compared with those trained by equal-spaced samples in generalizing performance. The results show that both the computational precision and stability of the former ANNs are more satisfactory than those of the latter. It is concluded that the flexibility of ANNs in generalizing can be effectively increased by use of uniformly distributed training samples rather than simply piling data.More reliable uniformity should be obtained, however, through NTMs instead of equal-spaced samples.  相似文献   
26.
应用三层ANN_BP网络解析苯和甲苯的吸收光谱 ,不经分离 ,用紫外分光光度法同时测定苯和甲苯 .使用改进的BP算法 ,避免了神经网络学习过程中可能产生的麻痹现象 ,提出了目标向量的简单变换方法及便于网络参数选择的收敛评价函数 .实验验证了方法的有效性 ,同时表明 ,苯在 0 - 72 0mg/L和甲苯在 0 - 84 0mg/L范围内服从比尔定律  相似文献   
27.
对前馈神经网络用于动态系统的辨识、自适应控制进行了分析和数学推导,给出了自适应神经网络控制器的设计方法.最后通过仿真实例进行了说明.  相似文献   
28.
设计了一套具有高性能的适合于移动数据网(超2.5G)和无线本地区域网(WLAN)组成的综合数据网的网络体系结构,提供基于预留端到端的QoS模型,使用带宽适应算法支持端到端的QOS,提高了系统资源的利用率,减少了呼叫拥塞概率和交接丢包概率,解决了2个系统QoS类不匹配等问题,平衡了2个系统的传输能力。  相似文献   
29.
可压缩流体网络的建模方法   总被引:3,自引:2,他引:1  
本文运用网络分析手段,首次提出了任意拓扑结构可压缩流体网络动态特性的建模方法.该方法突破了目前在流体网络分析中普遍采用的“小扰动”线性化处理方法的局限。  相似文献   
30.
The paper introduces the contributions to this special issue ofSystems Practice on Systems and Organizations: New Directions in terms ofdistal andproximal thinking. Distal thinking refers to ready-made concepts, to the finished effects and outcomes of thought and action; proximal thinking, to process and event, to the continuous and unfinished. The papers presented here deal with various aspects of the distal/proximal distinction in social systems and organizations, and especially draw out the implications of recent work in information technology, sociology of technology, accounting theory, and organization studies for a proximal conception of systems and organizations.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号