全文获取类型
收费全文 | 5541篇 |
免费 | 780篇 |
国内免费 | 565篇 |
专业分类
电工技术 | 614篇 |
综合类 | 479篇 |
化学工业 | 801篇 |
金属工艺 | 384篇 |
机械仪表 | 410篇 |
建筑科学 | 361篇 |
矿业工程 | 185篇 |
能源动力 | 275篇 |
轻工业 | 493篇 |
水利工程 | 206篇 |
石油天然气 | 156篇 |
武器工业 | 57篇 |
无线电 | 545篇 |
一般工业技术 | 525篇 |
冶金工业 | 330篇 |
原子能技术 | 169篇 |
自动化技术 | 896篇 |
出版年
2024年 | 43篇 |
2023年 | 113篇 |
2022年 | 255篇 |
2021年 | 305篇 |
2020年 | 200篇 |
2019年 | 131篇 |
2018年 | 187篇 |
2017年 | 167篇 |
2016年 | 181篇 |
2015年 | 272篇 |
2014年 | 266篇 |
2013年 | 365篇 |
2012年 | 427篇 |
2011年 | 479篇 |
2010年 | 432篇 |
2009年 | 457篇 |
2008年 | 466篇 |
2007年 | 388篇 |
2006年 | 415篇 |
2005年 | 349篇 |
2004年 | 276篇 |
2003年 | 158篇 |
2002年 | 141篇 |
2001年 | 123篇 |
2000年 | 110篇 |
1999年 | 56篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 7篇 |
1994年 | 16篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1959年 | 3篇 |
1957年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有6886条查询结果,搜索用时 31 毫秒
101.
武汉轨道交通2号线岩溶地段隧道工法研究 总被引:1,自引:0,他引:1
武汉地铁2号线虎泉站-光谷广场站区间隧道沿线灰岩分布广泛,岩溶发育,采取钻探、物探等综合勘探技术,查明了岩溶分布特性。在区间隧道施工前,进行了溶洞注浆加固处理;并在此基础上,对区间隧道矿山法、盾构法以及明挖法等工法进行了综合比较,提出了适应本地层条件下的矿山法施工方案,达到了预期的效果,可为类似工程的设计和施工提供借鉴。 相似文献
102.
Xianguang Gu Guangyong Sun Guangyao Li Lichen Mao Qing Li 《Structural and Multidisciplinary Optimization》2013,48(3):669-684
Design optimization without considering uncertainties of system variables and parameters can be problematic in real life. In order to take into account the effect of uncertainties, reliable and robust design schemes have proven effective, but limited studies have been reported to compare their difference in a multiobjective framework. This paper takes a typical vehicle structure subject to offset frontal crashing scenario as an example to compare reliable and robust designs with their deterministic counterpart. The thicknesses of some key components of vehicle frontal structures were selected as design variables, the vehicle weight and energy absorption as the objectives, deceleration and firewall intrusion as the constraints. The deterministic multiobjective optimization problem was first solved by adopting Design of Experimental (DOE), metamodels and Non-dominated Sorting Genetic Algorithm II (NSGA-II). Take into account the uncertainties, a Monte Carlo Simulation (MCS) is adopted to generate random distributions of the objective and constraint functions for each design. For the reliability-based optimization the desired reliabilities of 90 %, 95 % and 99 % are considered, respectively. For the robustness-based optimization, two different formulation strategies are adopted. The optimization showed that the reliable and robust Pareto fronts are shifted away from their deterministic counterpart due to uncertainties. The different Pareto fronts yielded from the deterministic, reliable and robust designs are compared to provide some quantitative insights into how to apply these different design schemes for resolving uncertainty problems. It is shown that, compared with the baseline design, the optimizations enhance the crashworthiness of vehicle, though more conservative solutions could have been generated from the reliable and robust optimizations. 相似文献
103.
Long Tang Hu Wang Guangyao Li Fengxiang Xu 《Structural and Multidisciplinary Optimization》2013,48(4):821-836
Although metamodel technique has been successfully used to enhance the efficiency of the multi-objective optimization (MOO) with black-box objective functions, the metamodel could become less accurate or even unavailable when the design variables are discrete. In order to overcome the bottleneck, this work proposes a novel random search algorithm for discrete variables based multi-objective optimization with black-box functions, named as k-mean cluster based heuristic sampling with Utopia-Pareto directing adaptive strategy (KCHS-UPDA). This method constructs a few adaptive sampling sets in the solution space and draws samples according to a heuristic probability model. Several benchmark problems are supplied to test the performance of KCHS-UPDA including closeness, diversity, efficiency and robustness. It is verified that KCHS-UPDA can generally converge to the Pareto frontier with a small quantity of number of function evaluations. Finally, a vehicle frontal member crashworthiness optimization is successfully solved by KCHS-UPDA. 相似文献
104.
The popular dynamic reanalysis methods, such as combined approximation (CA) mainly focus on frequency domain. Compared with time domain analysis, the main challenge for reanalysis methods is to calculate the responses in each iteration. Due to this difficulty, popular reanalysis methods are not available for time domain analysis, such as Newmark- $\beta $ and central different method (CDF). Therefore, a novel adaptive time-based global reanalysis (ATGR) algorithm for Newmark- $\beta $ method is suggested. If basis vectors are generated for predicting the response in each time step, computational cost of reanalysis should be significantly increased. To improve the efficiency, an adaptive reanalysis algorithm is suggested. Moreover, in order to enhance the accuracy of the popular combined algorithm (CA) reanalysis, a global strategy is suggested to construct basis vectors. Numerical examples show that accurate approximations are achieved efficiently for time domain problems. 相似文献
105.
提出了一种新的基于区域互信息和局部频率信息结合的双向图像配准测度。首先,以原参考图像为参考,计算出正向变换下图像的区域互信息和Gabor滤波后的得到局部频率
信息;同时,以输入图像为参考图像,计算出逆变换下的逆向互信息和局部频率信息。将正向与逆向变换下的互信息和局部频率信息各自相乘后求和,减去两幅图像对应的配准残
量,得到双向图像配准度量,用于对输入图像进行配准。仿真实验结果在验证分析结果的同时也表明,方法对图像噪声、分辨率等具有较高的鲁棒性,可有效提高配准的精度。 相似文献
106.
107.
108.
P2P系统中基于副本链的一致性维护算法 总被引:3,自引:1,他引:2
提出一种无结构纯P2P的副本一致性维护算法。利用副本节点发起的第一次更新消息在P2P网络中的广播,由其他收到消息的副本节点给出响应,构建副本链。副本链建立后,更新消息在副本节点间进行传播,不再在网络中洪泛。副本链的维护通过记录首次发起更新的副本节点IP地址完成。仿真试验证明该算法是简单有效的。 相似文献
109.
110.
非结构化P2P中搜索算法的性能分析 总被引:1,自引:0,他引:1
欧阳柏成 《计算机工程与科学》2009,31(6)
资源搜索是P2P应用所面临的最核心问题之一,相关的非结构化P2P系统主要采用了查询消息泛洪和信息索引机制.本文分析了非结构化P2P中几种典型的搜索算法,阐述了其搜索原理和搜索性能 .与其他研究不同,本文通过大量的模拟实验来验证搜索算法的性能;在不同网络规模中,通过对每一种搜索算法的查询成功率、搜索产生消息数和成功查询所用平均跳数进行比较分析,给出了相关结论. 相似文献