全文获取类型
收费全文 | 19535篇 |
免费 | 2754篇 |
国内免费 | 2002篇 |
专业分类
电工技术 | 3759篇 |
技术理论 | 1篇 |
综合类 | 2633篇 |
化学工业 | 737篇 |
金属工艺 | 221篇 |
机械仪表 | 1284篇 |
建筑科学 | 1015篇 |
矿业工程 | 387篇 |
能源动力 | 773篇 |
轻工业 | 302篇 |
水利工程 | 1385篇 |
石油天然气 | 343篇 |
武器工业 | 303篇 |
无线电 | 2776篇 |
一般工业技术 | 1373篇 |
冶金工业 | 313篇 |
原子能技术 | 42篇 |
自动化技术 | 6644篇 |
出版年
2024年 | 175篇 |
2023年 | 380篇 |
2022年 | 578篇 |
2021年 | 713篇 |
2020年 | 817篇 |
2019年 | 712篇 |
2018年 | 667篇 |
2017年 | 876篇 |
2016年 | 898篇 |
2015年 | 971篇 |
2014年 | 1348篇 |
2013年 | 1416篇 |
2012年 | 1525篇 |
2011年 | 1499篇 |
2010年 | 1066篇 |
2009年 | 1150篇 |
2008年 | 1179篇 |
2007年 | 1365篇 |
2006年 | 1085篇 |
2005年 | 889篇 |
2004年 | 774篇 |
2003年 | 677篇 |
2002年 | 501篇 |
2001年 | 440篇 |
2000年 | 409篇 |
1999年 | 324篇 |
1998年 | 247篇 |
1997年 | 243篇 |
1996年 | 214篇 |
1995年 | 172篇 |
1994年 | 157篇 |
1993年 | 118篇 |
1992年 | 114篇 |
1991年 | 95篇 |
1990年 | 90篇 |
1989年 | 80篇 |
1988年 | 62篇 |
1987年 | 28篇 |
1986年 | 15篇 |
1985年 | 20篇 |
1984年 | 27篇 |
1983年 | 20篇 |
1982年 | 26篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 28篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1976年 | 5篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 5 毫秒
1.
Redundancy allocation problem (RAP) is one of the best-developed problems in reliability engineering studies. This problem follows to optimize the reliability of a system containing s sub-systems under different constraints, including cost, weight, and volume restrictions using redundant components for each sub-system. Various solving methodologies have been used to optimize this problem, including exact, heuristic, and meta-heuristic algorithms. In this paper, an efficient multi-objective meta-heuristic algorithm based on simulated annealing (SA) is developed to solve multi-objective RAP (MORAP). This algorithm is knowledge-based archive multi-objective simulated annealing (KBAMOSA). KBAMOSA applies a memory matrix to reinforce the neighborhood structure to achieve better quality solutions. The results analysis and comparisons demonstrate the performance of the proposed algorithm for solving MORAP. 相似文献
2.
Load testing of applications is an important and costly activity for software provider companies. Classical solutions are very difficult to set up statically, and their cost is prohibitive in terms of both human and hardware resources. Virtualized cloud computing platforms provide new opportunities for stressing an application's scalability, by providing a large range of flexible and less expensive (pay‐per‐use model) computation units. On the basis of these advantages, load testing solutions could be provided on demand in the cloud. This paper describes a Benchmark‐as‐a‐Service solution that automatically scales the load injection platform and facilitates its setup according to load profiles. Our approach is based on: (i) virtualization of the benchmarking platform to create self‐scaling injectors; (ii) online calibration to characterize the injector's capacity and impact on the benched application; and (iii) a provisioning solution to appropriately scale the load injection platform ahead of time. We also report experiments on a benchmark illustrating the benefits of this system in terms of cost and resource reductions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
3.
Greg A. Breed Paul M. Severns Andrew M. Edwards 《Journal of the Royal Society Interface》2015,12(103)
Lévy flights have gained prominence for analysis of animal movement. In a Lévy flight, step-lengths are drawn from a heavy-tailed distribution such as a power law (PL), and a large number of empirical demonstrations have been published. Others, however, have suggested that animal movement is ill fit by PL distributions or contend a state-switching process better explains apparent Lévy flight movement patterns. We used a mix of direct behavioural observations and GPS tracking to understand step-length patterns in females of two related butterflies. We initially found movement in one species (Euphydryas editha taylori) was best fit by a bounded PL, evidence of a Lévy flight, while the other (Euphydryas phaeton) was best fit by an exponential distribution. Subsequent analyses introduced additional candidate models and used behavioural observations to sort steps based on intraspecific interactions (interactions were rare in E. phaeton but common in E. e. taylori). These analyses showed a mixed-exponential is favoured over the bounded PL for E. e. taylori and that when step-lengths were sorted into states based on the influence of harassing conspecific males, both states were best fit by simple exponential distributions. The direct behavioural observations allowed us to infer the underlying behavioural mechanism is a state-switching process driven by intraspecific interactions rather than a Lévy flight. 相似文献
4.
A double optimal projection method that involves projections for intra-cluster and inter-cluster dimensionality reduction are proposed for video fingerprinting. The video is initially set as a graph with frames as its vertices in a high-dimensional space. A similarity measure that can compute the weights of the edges is then proposed. Subsequently, the video frames are partitioned into different clusters based on the graph model. Double optimal projection is used to explore the optimal mapping points in a low-dimensional space to reduce the video dimensions. The statistics and geometrical fingerprints are generated to determine whether a query video is copied from one of the videos in the database. During matching, the video can be roughly matched by utilizing the statistics fingerprint. Further matching is thereafter performed in the corresponding group using geometrical fingerprints. Experimental results show the good performance of the proposed video fingerprinting method in robustness and discrimination. 相似文献
5.
流域泥沙灾害与泥沙资源性的研究 总被引:5,自引:0,他引:5
泥沙灾害与泥沙资源性是流域泥沙的重要属性,二者在一定条件下可以相互转化。本文论述了泥沙淤积、泥沙冲刷、岸滩崩塌、山地崩塌与泥石流、粗沙淤积的土地沙化等泥沙灾害,指出泥沙灾害具有时空分布的不均匀性、渐变性或突发性、群发性、转化性及危害严重性等;流域泥沙资源化的主要途径包括填海造陆及造地、引洪淤灌、堤防淤临淤背、建筑材料、湿地形成(河流、湖泊与河口海岸)等,指出流域泥沙资源化及其优化配置既要解决思想观念、基本理论、目标效益等方面的问题,还要考虑与水资源联合配置问题。 相似文献
6.
讨论了在VMI管理思想下对具有随机需求特性的多客户库存分配问题 ,重点论述了有效近似算法的设计过程 ,最后基于一组模拟数据给出了一个算例。 相似文献
7.
微制造平台微振动的最优控制 总被引:6,自引:0,他引:6
采用混合隔振技术建立了微制造平台隔振系统。该系统以空气弹簧和橡胶层作为被动隔振元件、超磁致伸缩致动器作为主动隔振元件,并采用最优控制理论设计其主动控制器。研究了在不同的性能指标加权阵的情况下,该主动振动控制系统对基础干扰和由微制造设备产生的直接干扰所引起的微制造平台振动的控制效果。研究表明性能指标加权阵对振动控制效果影响非常大。通过大量的仿真实验确定了一组性能指标加权阵,使所设计的主动控制系统能在较宽的频率范围对基础干扰和直接干扰所引起的微制造平台振动进行有效的控制。 相似文献
8.
ZhaoYahong ZhangZhongpei WuWeiling 《电子科学学刊(英文版)》2003,20(3):177-182
Adaptive modulation and power allocation is introduced into the multicarrier DSCDMA system to improve the system performance and bandwidth efficiency.First,the system design appropriate for adaptive modulation and power allocation is given,then the algorithm of adaptive modulation and power allocation is applied.Simulation results demonstrate great performance improvement compared with the fixed modulated one. 相似文献
9.
10.
本文提出一种关于DMT系统传输纯数据流业务的最佳的功率分配算法,该算法使用了一种有效的表格查手工艺工和拉格朗日乘法器对分搜索办法,能够较快的收敛到最佳的功率点。同时,易于用硬件和软件实现。 相似文献