全文获取类型
收费全文 | 131113篇 |
免费 | 21609篇 |
国内免费 | 14072篇 |
专业分类
电工技术 | 14617篇 |
技术理论 | 3篇 |
综合类 | 14589篇 |
化学工业 | 10198篇 |
金属工艺 | 4439篇 |
机械仪表 | 10984篇 |
建筑科学 | 4506篇 |
矿业工程 | 3589篇 |
能源动力 | 4660篇 |
轻工业 | 5087篇 |
水利工程 | 2856篇 |
石油天然气 | 3708篇 |
武器工业 | 2066篇 |
无线电 | 16837篇 |
一般工业技术 | 10986篇 |
冶金工业 | 3005篇 |
原子能技术 | 936篇 |
自动化技术 | 53728篇 |
出版年
2024年 | 1057篇 |
2023年 | 2704篇 |
2022年 | 4820篇 |
2021年 | 5259篇 |
2020年 | 5881篇 |
2019年 | 4934篇 |
2018年 | 4763篇 |
2017年 | 5665篇 |
2016年 | 6333篇 |
2015年 | 7153篇 |
2014年 | 9645篇 |
2013年 | 9576篇 |
2012年 | 11104篇 |
2011年 | 11451篇 |
2010年 | 8612篇 |
2009年 | 8924篇 |
2008年 | 8665篇 |
2007年 | 9563篇 |
2006年 | 7766篇 |
2005年 | 6408篇 |
2004年 | 5195篇 |
2003年 | 4164篇 |
2002年 | 3255篇 |
2001年 | 2654篇 |
2000年 | 2250篇 |
1999年 | 1737篇 |
1998年 | 1448篇 |
1997年 | 1173篇 |
1996年 | 942篇 |
1995年 | 746篇 |
1994年 | 613篇 |
1993年 | 473篇 |
1992年 | 426篇 |
1991年 | 263篇 |
1990年 | 282篇 |
1989年 | 215篇 |
1988年 | 139篇 |
1987年 | 65篇 |
1986年 | 62篇 |
1985年 | 58篇 |
1984年 | 48篇 |
1983年 | 48篇 |
1982年 | 51篇 |
1981年 | 22篇 |
1980年 | 38篇 |
1979年 | 35篇 |
1978年 | 15篇 |
1975年 | 15篇 |
1959年 | 20篇 |
1951年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
目前,基于因素空间理论的背景基提取算法计算过程复杂,初始化必须依赖各因素极值,基点数量提取冗余等原因,未能在应用中取得很好效果。为此,结合内点判别法和知识可继承、可扩展的思想,提出一种计算简单、初始化独立、基点数量小的改进的背景基提取算法。然后,利用改进的背景基提取算法构造出一种全新的数据分类算法-基点分类算法,基点分类算法以提取每一类样本的背景基为预测模型,再通过新定义的λ-背景基,优化预测模型。数值实验表明:基点分类算法原理简单、构造难度小、分类模型泛化能力强,预测能力准确率高,同时严格的模型限定区域又能为识别新类别提供新方法。 相似文献
72.
73.
以方竹笋中提取的膳食纤维为研究对象,采用动态高压微射流(dynamic high-pressure micro-fluidization, DHPM)在不同压力条件(0,50,100,150,200 MPa)下进行处理,探究其对竹笋膳食纤维(bamboo shoots dietary fiber, BSDF)理化和结构特性的影响。结果表明,随着处理压力的增大,BSDF粒径先增大后减小,当处理压力为150 MPa时,粒径最小,为(370±11) nm,此条件下BSDF的持水力、持油力和膨胀力达到最大,较对照组分别提高了47.74%,50.54%,61.27%,且差异显著(P<0.05)。红外光谱分析表明DHPM处理不会改变BSDF的官能团,但会使BSDF内部的部分氢键断裂和半纤维素、木质素等发生降解;X射线衍射和热重分析表明DHPM处理不会引起BSDF的晶体结构改变,但晶体有序度会下降,进而导致其热稳定性降低;微观结构分析显示DHPM处理会使BSDF颗粒尺寸减小、表面粗糙、组织松散,且当处理压力为200 MPa时,颗粒发生团聚。综上,DHPM可以有效改善BSDF的理化性质,在膳食纤维改性方面具有一定的应用价值。 相似文献
74.
75.
马钢二烧结配料计算机控制系统 总被引:1,自引:0,他引:1
阐明了马钢二烧结配科计算机控制系统的目的、控制形式、控制原理;根据烧结配料控制对象的特点对信号采样和控制算法进行了探讨;提供了系统的主要硬件结构,软件功能和程序框图。 相似文献
76.
Namyong Kim 《ETRI Journal》2006,28(2):155-161
In this paper, we introduce an escalator (ESC) algorithm based on the least squares (LS) criterion. The proposed algorithm is relatively insensitive to the eigenvalue spread ratio (ESR) of an input signal and has a faster convergence speed than the conventional ESC algorithms. This algorithm exploits the fast adaptation ability of least squares methods and the orthogonalization property of the ESC structure. From the simulation results, the proposed algorithm shows superior convergence performance. 相似文献
77.
78.
基于进化算法的常减压装置模拟 总被引:1,自引:0,他引:1
提出了基于优选优生进化算法(Select—best and prepotency evolution algorithm,SPEA)的常减压装置模拟方法。以各塔的温度分布为目标,基于生产过程和分析数据,采用SPEA确定各塔板Murphree效率,从而精确描述各塔板平衡偏离程度。在实际应用中,获得具有良好精度的常减压装置模型。系统分析了SPEA算法的关键参数——优选领域大小与计算复杂性及寻优性能之间的关系,结果显示其取值为群体规模的10%最为合适。 相似文献
79.
80.
Depending on whether bidirectional links or unidirectional links are used for communications, the network topology under a
given range assignment is either an undirected graph referred to as the bidirectional topology, or a directed graph referred
to as the unidirectional topology. The Min-Power Bidirectional (resp., Unidirectional) k-Node Connectivity problem seeks a range assignment of minimum total power subject to the constraint that the produced bidirectional
(resp. unidirectional) topology is k-vertex connected. Similarly, the Min-Power Bidirectional (resp., Unidirectional) k-Edge Connectivity problem seeks a range assignment of minimum total power subject to the constraint the produced bidirectional
(resp., unidirectional) topology is k-edge connected.
The Min-Power Bidirectional Biconnectivity problem and the Min-Power Bidirectional Edge-Biconnectivity problem have been studied
by Lloyd et al. [23]. They show that range assignment based the approximation algorithm of Khuller and Raghavachari [18],
which we refer to as Algorithm KR, has an approximation ratio of at most 2(2 – 2/n)(2 + 1/n) for Min-Power Bidirectional Biconnectivity, and range assignment based on the approximation algorithm of Khuller and Vishkin [19],
which we refer to as Algorithm KV, has an approximation ratio of at most 8(1 – 1/n) for Min-Power Bidirectional Edge-Biconnectivity.
In this paper, we first establish the NP-hardness of Min-Power Bidirectional (Edge-) Biconnectivity. Then we show that Algorithm KR has an approximation ratio of at most 4 for both Min-Power Bidirectional Biconnectivity and Min-Power Unidirectional Biconnectivity,
and Algorithm KV has an approximation ratio of at most 2k for both Min-Power Bidirectional k-Edge Connectivity and Min-Power Unidirectional k-Edge Connectivity. We also propose a new simple constant-approximation algorithm for both Min-Power Bidirectional Biconnectivity
and Min-Power Unidirectional Biconnectivity. This new algorithm applies only to Euclidean instances, but is best suited for
distributed implementation.
A preliminary version of this work appeared in the proceedings of the 2nd International Conference on AD-HOC Network and Wireless
(Adhoc-Now 2003).
Research performed in part while visiting the Max-Plank-Institut fur Informatik.
Gruia Calinescu is an Assistant Professor of Computer Science at the Illinois Institute of Technology since 2000. He held postdoc or visiting
researcher positions at DIMACS, University of Waterloo, and Max-Plank Institut fur Informatik. Gruia has a Diploma from University
of Bucharest and a Ph.D. from Georgia Insitute of Technology. His research interests are in the area of algorithms.
Peng-Jun Wan has joined the Computer Science Department at Illinois Institute of Technology in 1997 and has been an Associate Professor
since 2004. He received his Ph.D. in Computer Science from University of Minnesota in 1997, M.S. in Operations Research and
Control Theory from Chinese Academy of Science in 1993, and B.S. in Applied Mathematics from Tsinghua University in 1990.
His research interests include optical networks and wireless networks. 相似文献