全文获取类型
收费全文 | 6705篇 |
免费 | 272篇 |
国内免费 | 724篇 |
专业分类
系统科学 | 1071篇 |
丛书文集 | 188篇 |
教育与普及 | 21篇 |
理论与方法论 | 6篇 |
现状及发展 | 83篇 |
综合类 | 6332篇 |
出版年
2024年 | 39篇 |
2023年 | 64篇 |
2022年 | 87篇 |
2021年 | 92篇 |
2020年 | 118篇 |
2019年 | 81篇 |
2018年 | 78篇 |
2017年 | 125篇 |
2016年 | 131篇 |
2015年 | 205篇 |
2014年 | 303篇 |
2013年 | 275篇 |
2012年 | 422篇 |
2011年 | 445篇 |
2010年 | 346篇 |
2009年 | 436篇 |
2008年 | 460篇 |
2007年 | 526篇 |
2006年 | 440篇 |
2005年 | 407篇 |
2004年 | 340篇 |
2003年 | 288篇 |
2002年 | 245篇 |
2001年 | 238篇 |
2000年 | 221篇 |
1999年 | 219篇 |
1998年 | 197篇 |
1997年 | 174篇 |
1996年 | 169篇 |
1995年 | 141篇 |
1994年 | 94篇 |
1993年 | 70篇 |
1992年 | 61篇 |
1991年 | 38篇 |
1990年 | 42篇 |
1989年 | 37篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1955年 | 3篇 |
排序方式: 共有7701条查询结果,搜索用时 15 毫秒
21.
杨芳 《广西师范学院学报(自然科学版)》2008,(3):26-29
研究了具有第Ⅱ类功能性反应的三种群捕食-食饵离散系统,得到了保证该系统持久性的充分条件. 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.
袁邓彬 《上饶师范学院学报》2007,27(3):18-20,25
研究了板几何中一类具非对称散射裂变核的迁移算子的谱,证明了该算子在右半平面无复本征值和存在有限个具有限代数重数的实离散本征值。 相似文献
24.
Alexandra Sauer 《Systemic Practice and Action Research》2008,21(6):497-515
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
25.
26.
本文通过构造双参数量子群SUqs(1,1)生成元的qs-Boson实现,给出了SUqs(1,1)的正离散序列表示。 相似文献
27.
Samples Selection for Artificial Neural Network Training in Preliminary Structural Design 总被引:1,自引:0,他引:1
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
28.
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
29.
一种改进的实信号IFFT算法 总被引:1,自引:0,他引:1
由于重量轻、体积小、功耗低、功能强的小卫星工作在无人干预的低温 ,高辐射的空间环境中 ,因此星上计算机系统必须满足集成度高、寿命长、可靠性高、抗辐射能力强的要求。针对立体测绘小卫星的特点 ,我们设计了满足上述要求的集集中控制与分布控制优点于一身的星上计算机系统 ,对其可靠性进行了分析 ,并对提高其可靠性应采取的关键技术进行了简要的论述。 相似文献
30.
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