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   4748篇
  免费   684篇
  国内免费   255篇
电工技术   327篇
综合类   367篇
化学工业   785篇
金属工艺   317篇
机械仪表   246篇
建筑科学   383篇
矿业工程   188篇
能源动力   135篇
轻工业   234篇
水利工程   89篇
石油天然气   312篇
武器工业   50篇
无线电   606篇
一般工业技术   683篇
冶金工业   277篇
原子能技术   42篇
自动化技术   646篇
  2024年   50篇
  2023年   141篇
  2022年   244篇
  2021年   338篇
  2020年   259篇
  2019年   186篇
  2018年   188篇
  2017年   206篇
  2016年   205篇
  2015年   262篇
  2014年   286篇
  2013年   257篇
  2012年   305篇
  2011年   349篇
  2010年   273篇
  2009年   249篇
  2008年   234篇
  2007年   182篇
  2006年   228篇
  2005年   197篇
  2004年   111篇
  2003年   117篇
  2002年   98篇
  2001年   85篇
  2000年   94篇
  1999年   80篇
  1998年   70篇
  1997年   80篇
  1996年   72篇
  1995年   45篇
  1994年   39篇
  1993年   35篇
  1992年   27篇
  1991年   19篇
  1990年   20篇
  1989年   16篇
  1988年   13篇
  1987年   3篇
  1986年   4篇
  1985年   5篇
  1984年   2篇
  1983年   1篇
  1982年   2篇
  1981年   3篇
  1980年   2篇
  1979年   1篇
  1968年   1篇
  1965年   1篇
  1959年   1篇
  1956年   1篇
排序方式: 共有5687条查询结果,搜索用时 17 毫秒
11.
提出寻迹与搬运机器人的一种智能控制系统设计;该系统主要由单片机、传感器和执行舵机组成;通过分析直行、弯道与取物等工作模式,建立相应的舵机驱动控制;传感器将检测到的路线和工件信号传送给单片机进行处理;按照不同的优先级别,由单片机发出脉冲信号,控制舵机的速度与方向,完成抓取、转运工件的任务;实验结果表明:多路传感器的信息融合能有效识别寻迹路径,确定优先级别的控制;舵机的驱动控制能满足寻迹与搬运的要求;系统设计简单,实用可靠,具有良好的开放性与扩展性.  相似文献   
12.
Customs and quarantine departments are applying information systems to automate their inspection processes and improve their inspection efficiency and accuracy. The product codes from the Harmonized System (HS codes) are the essential elements of the system's integration, automation and intelligence. The identified HS codes are well-accepted and precise product references used by customs authorities, to match applicable policies to the products being inspected and taxed. Domain ontology for importing and exporting industry can be used to acquire HS codes for given products, and is a prerequisite for an integrated and intelligent automated inspection system. The authors have proposed and implemented an importing and exporting domain ontology. The ontology is composed of an integrated and comprehensive knowledge base derived from static dictionaries and the HS specification, and dynamic processing data. Based on this ontology, a reasoning engine is developed to generate HS codes intelligently for the given product names. Information systems can use the engine to get HS codes for submitted products and find applicable policies automatically. The ontology and the engine have been implemented in a Java-based platform and published as a HS Web service. In this paper, knowledge structure, reasoning mechanism and implementation details for the domain ontology and reasoning engine are presented. A test bed in the application environment has been conducted and experimental results have been obtained. The ontology and the service have the potential to be widely used by authorities and international traders of importing and exporting industry around the world.  相似文献   
13.
提出一种将USB接口和短距离无线通信相结合的无线USB高速数据传输系统的设计方案,阐述该系统的软硬件设计方案和工作原理。该方案采用Cypress公司的片上可编程芯片CYWUSB6935进行无线收发,使用NI—VISA驱动USB接口,利用图形化编程语言LabVIEW开发应用程序。实验证明,该系统在短距离无线通信时具有较高的数据传输速率,在工业控制中有较高的应用价值。  相似文献   
14.
15.
根据电测井曲线可以了解地层构造.为了找出含水砂层,基于人工分层的原理,利用小波变换过零点理论对电测井曲线进行计算机自动分层,将地下土层分为含水层和隔水层.介绍小波变换原理,给出用Matlab软件实现测井曲线计算机自动分层的方法.实验结果表明,用该方法研究实测井信号,结果与人工方法基本一敛,证明了小波变换用于测井信号分析与处理的有效性.论文工作对合理利用地下水资源有非常重要的意义.  相似文献   
16.
Due to the complicated blasting load, the diversified medium models and various constitutive relations of the rock mass, and a huge job for simulating blasting of multiple holes, it is very difficult and costly to simulate the blasting vibration accurately in numerical computation. This paper presents an equivalent simulation method so as to transform this complex dynamic problem into an approximate initial-boundary problem. The equivalent elastic boundary applied by the blasting load was developed for multiple holes according to the spatial distribution of rock damage around each blasthole. The equivalent mechanics process of the complex blasting load was performed through analysis of the expansion of the borehole volume, the growth of cracks, the movement of stemming and the outburst of detonation gases. In combination with the blasting excavation of the tailrace tunnel in the Pubugou Hydropower Station, particle vibration velocities in the surrounding rock at different distances from the explosion source were simulated by applying this equivalent method based on the dynamic finite element method. The comparison with field monitoring data indicates that this equivalent simulation method is applicable to predicting the far-field dynamic response of the ground subjected to blasting load, and the selection of rock mass properties near the equivalent elastic boundary has a significant impact on simulation results.  相似文献   
17.
This paper presents an unsupervised structural damage pattern recognition approach based on the fuzzy clustering and the artificial immune pattern recognition (AIPR). The fuzzy clustering technique is used to initialize the pattern representative (memory cell) for each data pattern and cluster training data into a specified number of patterns. To improve the quality of memory cells, the artificial immune pattern recognition method based on immune learning mechanisms is employed to evolve memory cells. The presented hybrid immune model (combined with fuzzy clustering and the artificial immune pattern recognition) has been tested using a benchmark structure proposed by the IASC–ASCE (International Association for Structural Control–American Society of Civil Engineers) Structural Health Monitoring Task Group. The test results show the feasibility of using the hybrid AIPR (HAIPR) method for the unsupervised structural damage pattern recognition.  相似文献   
18.
19.
Dimension reduction methods are often applied in machine learning and data mining problems. Linear subspace methods are the commonly used ones, such as principal component analysis (PCA), Fisher's linear discriminant analysis (FDA), common spatial pattern (CSP), et al. In this paper, we describe a novel feature extraction method for binary classification problems. Instead of finding linear subspaces, our method finds lower-dimensional affine subspaces satisfying a generalization of the Fukunaga–Koontz transformation (FKT). The proposed method has a closed-form solution and thus can be solved very efficiently. Under normality assumption, our method can be seen as finding an optimal truncated spectrum of the Kullback–Leibler divergence. Also we show that FDA and CSP are special cases of our proposed method under normality assumption. Experiments on simulated data show that our method performs better than PCA and FDA on data that is distributed on two cylinders, even one within the other. We also show that, on several real data sets, our method provides statistically significant improvement on test set accuracy over FDA, CSP and FKT. Therefore the proposed method can be used as another preliminary data-exploring tool to help solve machine learning and data mining problems.  相似文献   
20.
This study proposed a method for developing high spatial resolution Gaofen-1 satellite (GF-1) Wide Field Imager (WFI)-based total suspended matter concentration (CTSM) retrieval model with the assistance of Moderate Resolution Imaging Spectroradiometer (MODIS) data, using the Deep Bay in China as a case. Based on long-term calibrated CTSM measurements of optical backscatter (OBS) 3A turbidity and temperature monitoring system of two stationary stations from January 2007 through November 2008, 33 match-ups were selected to build an exponential retrieval model for MODIS atmospherically corrected remote-sensing reflectance (Rrs) ratio (Rrs,645/Rrs,555). Validation of the MODIS model showed well agreement with the seven in situ CTSM measurements with a root mean squared error (RMSE) of 5.06 mg l?1 and a coefficient of determination R2 of 0.80. Aided with six MODIS retrieved CTSM products, different band combinations (single band (Rrc,660), band subtraction (Rrc,660Rrc,560), band ratio (Rrc,660/Rrc,560), and total suspended matter index at 660 nm band (TSMI660) were evaluated for simultaneous GF-1 WFI Rayleigh-corrected reflectance (Rrc). The results showed that the exponential model based on the Rayleigh-corrected reflectance ratio (Rrc,660/Rrc,560) could achieve acceptable accuracy, with RMSE of 14.80 mg l?1 and R2 of 0.62. The proposed method would be helpful for dynamic monitoring in the Deep Bay, and more important could also provide an alternative approach for studies when in situ measurements are unreachable.  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