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   15544篇
  免费   1264篇
  国内免费   572篇
电工技术   831篇
技术理论   1篇
综合类   1074篇
化学工业   2710篇
金属工艺   1037篇
机械仪表   1021篇
建筑科学   1214篇
矿业工程   569篇
能源动力   427篇
轻工业   874篇
水利工程   243篇
石油天然气   1136篇
武器工业   128篇
无线电   1422篇
一般工业技术   1855篇
冶金工业   887篇
原子能技术   150篇
自动化技术   1801篇
  2024年   80篇
  2023年   316篇
  2022年   464篇
  2021年   686篇
  2020年   523篇
  2019年   389篇
  2018年   498篇
  2017年   530篇
  2016年   454篇
  2015年   600篇
  2014年   719篇
  2013年   870篇
  2012年   935篇
  2011年   1044篇
  2010年   882篇
  2009年   824篇
  2008年   815篇
  2007年   777篇
  2006年   809篇
  2005年   722篇
  2004年   483篇
  2003年   478篇
  2002年   504篇
  2001年   441篇
  2000年   369篇
  1999年   412篇
  1998年   329篇
  1997年   262篇
  1996年   243篇
  1995年   220篇
  1994年   161篇
  1993年   103篇
  1992年   99篇
  1991年   67篇
  1990年   61篇
  1989年   53篇
  1988年   43篇
  1987年   24篇
  1986年   12篇
  1985年   16篇
  1984年   20篇
  1983年   2篇
  1982年   17篇
  1981年   7篇
  1980年   8篇
  1979年   4篇
  1977年   2篇
  1976年   1篇
  1975年   1篇
  1973年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
This paper presents a new robust optimization method for supply chain network design problem by employing variable possibility distributions. Due to the variability of market conditions and demands, there exist some impreciseness and ambiguousness in developing procurement and distribution plans. The proposed optimization method incorporates the uncertainties encountered in the manufacturing industry. The main motivation for building this optimization model is to make tools available for producers to develop robust supply chain network design. The modeling approach selected is a fuzzy value-at-risk (VaR) optimization model, in which the uncertain demands and transportation costs are characterized by variable possibility distributions. The variable possibility distributions are obtained by using the method of possibility critical value reduction to the secondary possibility distributions of uncertain demands and costs. We also discuss the equivalent parametric representation of credibility constraints and VaR objective function. Furthermore, we take the advantage of structural characteristics of the equivalent optimization model to design a parameter-based domain decomposition method. Using the proposed method, the original optimization problem is decomposed to two equivalent mixed-integer parametric programming sub-models so that we can solve the original optimization problem indirectly by solving its sub-models. Finally, we present an application example about a food processing company with four suppliers, five plants, five distribution centers and five customer zones. We formulate our application example as parametric optimization models and conduct our numerical experiments in the cases when the input data (demands and costs) are deterministic, have fixed possibility distributions and have variable possibility distributions. Experimental results show that our parametric optimization method can provide an effective and flexible way for decision makers to design a supply chain network.  相似文献   
112.
Fire detection is an important task in many applications. Smoke and flame are two essential symbols of fire in images. In this paper, we propose an algorithm to detect smoke and flame simultaneously for color dynamic video sequences obtained from a stationary camera in open space. Motion is a common feature of smoke and flame and usually has been used at the beginning for extraction from a current frame of candidate areas. The adaptive background subtraction has been utilized at a stage of moving detection. In addition, the optical flow-based movement estimation has been applied to identify a chaotic motion. With the spatial and temporal wavelet analysis, Weber contrast analysis and color segmentation, we achieved moving blobs classification. Real video surveillance sequences from publicly available datasets have been used for smoke detection with the utilization of our algorithm. We also have conducted a set of experiments. Experiments results have shown that our algorithm can achieve higher detection rate of 87% for smoke and 92% for flame.  相似文献   
113.
we present a novel polarimetric synthetic aperture radar (PolSAR) image compression scheme. PolSAR data contains lots of similar redundancies in single-channel and massively correlation between polarimetric channels. So these features make it difficult to represent PolSAR data efficiently. In this paper, discrete cosine transform (DCT) is adopted to remove redundancies between polarimetric channels, simple but quite efficient in improving compressibility. Sparse K-singular value decomposition (K-SVD) dictionary learning algorithm is utilized to remove redundancies within each channel image. Double sparsity scheme will be able to achieve fast convergence and low representation error by using a small number of sparsity dictionary elements, which is beneficial for the task of PolSAR image compression. Experimental results demonstrate that both numerical evaluation indicators and visual effect of reconstructed images outperform other methods, such as SPIHT, JPEG2000, and offline method.  相似文献   
114.
The global skyline, as an important variant of the skyline, has been widely applied in multi-criteria decision making, business planning and data mining. In this paper, we extend our early work and propose the maintenance methods to process the subspace global skyline (SGS) queries in dynamic databases. In the previous work, we proposed the index structure RB-tree, which can effectively manage the data to accelerate the subspace global skyline calculation. Also, the basic single SGS algorithm based on RB-tree (SSRB) and the optimized single SGS algorithm (OSSRB) were proposed to process a single SGS query. In addition, the multiple SGS algorithm (MSRB) was proposed to calculate multiple SGS queries by sharing the scan spaces of different queries. In this paper, we design some data structures and propose the maintenance approaches of SSRB, OSSRB and MSRB to cope with updates that happen to data sets. Thus our extended algorithms can be adopted for dynamic data sets. Finally, the experimental results show that the proposed algorithms OSSRB and MSRB have good performance to process SGS queries and they can be easily maintained with dynamic datasets.  相似文献   
115.
A considerable part of the literature on fuzzy sets is devoted to the field of fuzzy control system. In this paper, an alternative control system is introduced to describe a dynamic system with fuzzy white noise. In order to find optimal ways to control such a system, fuzzy optimal control theory is further developed. Specifically, a linear quadratic model is formulated and solved as a fuzzy optimal control problem. The formulation and solution of this model provide an economic interpretation of a production planning model both in the finite horizon and in the infinite horizon.  相似文献   
116.
Many decision-makers in industry, government and academia routinely make decisions whose outcome depends on the evolution of software technology trends. Even though the stakes of these decisions are usually very high, decision makers routinely depend on expert opinions and qualitative assessments to model the evolution of software technology; both of these sources of decision-making information are subjective, are based on opinions rather than facts, and are prone to error. In this paper, we report on our ongoing work to build quantitative models of the evolution of software technology trends. In particular, we discuss how we took specific evolutionary models and merged them into a single (general-purpose) model. The original specific models are derived empirically using statistical methods on trend data we had collected over several years, and have been validated individually; in this paper we further validate the generic (general-purpose) model.  相似文献   
117.
基于卟啉阵列传感器和毒气接触发生化学反应导致其色谱变化的“指纹”特性原理,提出了一种以嵌入式ARM9 S3C2440A为核心、以Linux为操作系统、QT/Embedded为开发工具并利用卟啉化学传感器的痕量毒气检测装置.阐述了系统总体设计,实现了卟啉传感阵列光谱信号采集、信号处理、反应环境监控等主要功能模块及控制软件...  相似文献   
118.
描述了一种基于DSP、CPLD及计算机串口通信,针对薄带传输过程中出现的跑偏问题的电磁纠偏数字控制系统,并在理论分析基础上通过实验验证了该系统运行可靠、纠偏控制精度高。为电磁纠偏辊的进一步发展奠定基础。  相似文献   
119.
3种不同产地生地黄近红外图谱的判别分析   总被引:2,自引:0,他引:2  
目的:采用近红外漫反射光谱技术对3种不同产地的生地黄进行近红外漫反射指纹图谱判别分析,建立基于近红外漫反射图谱的快速、简便的鉴别方法.方法:用Nico1et6700型傅里叶变换近红外光谱仪采集光谱,在OPUS5.5分析软件上用二阶导数+矢量归一化法进行产地聚类.结果:3种不同产地的生地黄距离在0.6以上时被分开,15批验证集的样品中2份判断错误,预测集正确率为86.67%.结论:此方法简便可行,可为地黄产地鉴别方法提供1种新技术.  相似文献   
120.
对于分布式多媒体系统,创建合适的结构模型是其重要的研究课题之一。文章在基于模式转换的思想基础上,提出了一种分布式多媒体系统的结构模型,该模型可有效地支持多媒体对象的表现和通信。  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