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   2054篇
  免费   232篇
  国内免费   28篇
电工技术   22篇
综合类   36篇
化学工业   345篇
金属工艺   32篇
机械仪表   45篇
建筑科学   60篇
矿业工程   29篇
能源动力   157篇
轻工业   954篇
水利工程   28篇
石油天然气   116篇
无线电   66篇
一般工业技术   162篇
冶金工业   14篇
原子能技术   5篇
自动化技术   243篇
  2024年   17篇
  2023年   87篇
  2022年   99篇
  2021年   111篇
  2020年   126篇
  2019年   101篇
  2018年   93篇
  2017年   75篇
  2016年   135篇
  2015年   121篇
  2014年   149篇
  2013年   114篇
  2012年   130篇
  2011年   108篇
  2010年   107篇
  2009年   101篇
  2008年   58篇
  2007年   106篇
  2006年   112篇
  2005年   62篇
  2004年   28篇
  2003年   39篇
  2002年   45篇
  2001年   44篇
  2000年   25篇
  1999年   32篇
  1998年   21篇
  1997年   5篇
  1996年   20篇
  1995年   12篇
  1994年   5篇
  1993年   5篇
  1992年   1篇
  1991年   8篇
  1990年   7篇
  1989年   4篇
  1982年   1篇
排序方式: 共有2314条查询结果,搜索用时 31 毫秒
31.
为把用实数表示的指纹特征模板应用到密钥生成和密钥隐藏等密码学实践中,在详细分析已有量化算法的基础上,研究了指纹模板的量化问题,讨论了不同的量化思路,提出了两种非均衡特征向量量化方法和一种复合特征向量量化方法。通过计算原始模板和3种量化情况下特征向量几何距(汉明距)的分布及错误接受率的错误拒绝率的变化情况,比较了两种量化方法和复合量化方法的优劣。实验结果表明,量化方法二优于量化方法一,而复合量化方法优于这两种方法。  相似文献   
32.
In recent years, one of the most important and promising research fields has been metaheuristics to find optimal or near-optimal solutions for NP-hard combinatorial optimization problems. Improving the quality of the solution or the solution time is basic research area on metaheuristics. Modifications of the existing ones or creation of hybrid approaches are the focus of these efforts. Another area of improving the solution quality of metaheuristics is finding the optimal combination of algorithm control parameters. This is usually done by design of experiments or one-at-a-time approach in genetic algorithms, simulated annealing and similar metaheuristics. We observe that, in studies which use Ant Colonies Optimization (ACO) as an optimization technique; the levels of control parameters are determined by some non-systematic initial experiments and the interactions of the parameters are not studied yet.In this study, the parameters of Ant System have been investigated on different sized and randomly generated job-shop scheduling problems by using design of experiments. The effects and interactions of the parameters have been interpreted with the outputs of the experiments. Referring to the statistical analysis it is observed that none of the interactions between the Ant System parameters has a significant effect on makespan value. A specific fractional experimental design is suggested instead of the full factorial design. Depending on the findings from the benchmark problems it will be a reliable approach to use the suggested design for saving time and effort in experiments without sacrificing the solution quality.  相似文献   
33.
为面向学者的社交网络系统中的用户构建学术圈,对促进学者之间的交流具有重要的应用价值。根据学者之间的共同属性进行相似度计算,形成学术领域相似和研究课题相近的学术圈,能让学者们更加紧密和频繁地协同合作。提出了利用学者的学术信息提取代表个人特征的学术标签,并对不同类别标签的权重进行衡量,再通过相似度计算和聚类算法构建学术圈的方法。通过抓取学者社交网络平台SCHOLAT公开的学者信息进行实验,进而验证所提方法的可靠性和实用性。  相似文献   
34.
While simple crop and hydrological models are limited with respect to the number and accuracy of the processes they incorporate, complex models have high demand for data. Due to the limitations of both categories of models, there is a need for new agro-hydrological models that simulate both crop productivity and water availability in agricultural catchments, with low data and calibration requirements. This study aimed at developing a widely applicable parsimonious agro-hydrological model, AquaCrop-Hydro, which couples the AquaCrop crop water productivity model with a conceptual hydrological model. AquaCrop-Hydro, simulating crop productivity, the daily soil water balance and discharge at the catchment outlet, performed well for an agricultural catchment in Belgium. The model can be used to investigate the effect of agricultural management and environmental changes from field to catchment scale in support of sustainable water management in agricultural areas.  相似文献   
35.
廖彬  杜明辉  胡金龙 《计算机科学》2011,38(5):272-274,300
形变物体边界的准确定位是光流估计的难点之一,仅依靠改进光流算法收效甚微。提出了全自动生长分割,以准确提取形变运动物体,从而将视频分割结果与梯度彩色光流算法相结合来提高光流法对形变物体的检测准确法度  相似文献   
36.
This paper presents a multi-robot open architecture of an intelligent computer numerical control (CNC) system based on parameter-driven technology that has been developed for flexible and high-efficiency manipulation. An open architecture control system capable of distributed processing of decision-making and extraction of task information provides a premise for intelligent control and flexible operation. Intelligent detection with database feedback based on real-time assignment of tasks is proposed to achieve dynamic modification of the processing trajectory. In the context of flexible task control, a multi-robot architecture with collision-free path planning and a novel programming approach based on parameter-driven technology are developed. The proposed CNC system has been successfully implemented and demonstrated on an H-beam steel-cutting task that requires flexible and accurate machining.  相似文献   
37.
以酒精含量为指标,筛选发酵性能最好的混菌酵母组合.通过Plackett-Burman试验设计筛选出影响荔枝酒发酵工艺的3个主要因素.响应面优化确定了混菌发酵荔枝酒的最佳工艺参数:发酵温度17.86℃,pH3.47,接种量9.74%(V/V),酒精含量达12.53%(V/V).对比分析了混菌发酵与单菌发酵荔枝酒中主要风味成分的变化.结果表明:混菌发酵降低了有机酸总量,使酒体协调性增加,增加的氨基酸总量赋予了荔枝酒较高的营养价值;混菌发酵的荔枝酒感官评分高于单菌发酵.  相似文献   
38.
针对高校数字校园建设的需要,提出基于J2EE和工作流技术的办公自动化设计方案。介绍了OA系统的优点。讨论了系统的整体设计目标和在设计时要注意的问题,阐述了系统的整体结构和工作流平台系统的构成。  相似文献   
39.
In this study, the potential of organic acids (formic acid, acetic acid) in a catalytical and mechanocatalytic conversion of lignocellulosic barley straw to valuable sugars is explored using sulfuric acid as a reference. Acid-catalyzed hydrolysis has been carried out with acid-impregnated samples as well as unmodified barley straw. In the mechanocatalytical approach, pretreatment consists of impregnation with the acid catalyst and mechanical treatment by ball milling following chemical hydrolysis. Straw samples and residues were analyzed by Fourier transform infrared spectrometry (FT-IR) whereas hydrolysate analysis was based on total reducing sugar (TRS) determination following the DNS method and capillary electrophoresis (CE) analysis. The results indicated that acetic acid and formic acid are rather mild acids yielding low TRS levels compared to the reference acid. Mechanocatalytical pretreatment slightly increased TRS yields, but not significantly. Strikingly, sulfuric acid showed an efficient conversion efficiency yielding almost 45% of TRS. Furthermore, this study provided evidence for the acetylation of straw components when acetic acid was used as catalyst. Alkali hydrolysis induced the de-esterification, but revealed no significant increase of TRS yields.  相似文献   
40.
Enriched concentrations of metal contaminants have been reported in surficial sediments and tissues of aquatic organisms in Sydney estuary, New South Wales, Australia. Dietary ingestion of contaminated, suspended sediments is potentially a major route of metal exposure to the filter-feeder Saccostrea glomerata. A dynamically coupled biokinetic-equilibrium bioaccumulation model was developed to explore sediment-oyster-metal uptake interactions. The biokinetic component simulated the sediment dynamics and oyster uptake and loss kinetics while the ion equilibrium model accounted for the metal speciation reactions. Results of a laboratory-based mesocosm experiment as well as data from the literature were used to parameterise the model. The model demonstrated a good fit of the experimental data and indicated that dissolved and particulate organic matter were important determinants of metal bioavailability to this species. The model served also as a unique tool to formulate testable hypotheses and help to better explain the bioaccumulation patterns observed from the experiment.  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