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   277808篇
  免费   3326篇
  国内免费   1304篇
电工技术   4800篇
综合类   519篇
化学工业   40245篇
金属工艺   11123篇
机械仪表   8414篇
建筑科学   6393篇
矿业工程   1575篇
能源动力   6966篇
轻工业   22455篇
水利工程   3035篇
石油天然气   5781篇
武器工业   43篇
无线电   33487篇
一般工业技术   56432篇
冶金工业   50861篇
原子能技术   7489篇
自动化技术   22820篇
  2021年   2151篇
  2019年   2060篇
  2018年   3574篇
  2017年   3668篇
  2016年   3897篇
  2015年   2484篇
  2014年   4344篇
  2013年   11956篇
  2012年   7060篇
  2011年   9699篇
  2010年   7528篇
  2009年   8744篇
  2008年   9090篇
  2007年   9129篇
  2006年   7800篇
  2005年   7246篇
  2004年   7196篇
  2003年   6972篇
  2002年   6713篇
  2001年   6844篇
  2000年   6476篇
  1999年   6760篇
  1998年   16295篇
  1997年   11578篇
  1996年   8915篇
  1995年   6843篇
  1994年   6012篇
  1993年   6051篇
  1992年   4395篇
  1991年   4180篇
  1990年   4073篇
  1989年   4055篇
  1988年   3750篇
  1987年   3387篇
  1986年   3392篇
  1985年   3739篇
  1984年   3460篇
  1983年   3217篇
  1982年   3024篇
  1981年   3038篇
  1980年   3030篇
  1979年   2829篇
  1978年   2869篇
  1977年   3141篇
  1976年   4096篇
  1975年   2416篇
  1974年   2379篇
  1973年   2396篇
  1972年   2018篇
  1971年   1781篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
Replicated W. K. Kirchner and M. D. Dunnette's (see record 1955-03161-001) study on attitudes toward older workers with 71 male and 5 female hourly employees (aged 18–61 yrs) and 22 male supervisors (aged 27–63 yrs) of a nonunion manufacturing plant. Ss completed a questionnaire that was nearly identical to the one administered in the Kirchner and Dunnette study. Results are similar to those obtained in the earlier study: Hourly workers held more positive attitudes toward older employees than did supervisors, and attitude score correlated strongly with the age of hourly workers but not with the age of supervisors. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
974.
Self-powered wireless temperature sensors exploit RFID technology   总被引:3,自引:0,他引:3  
Emerging RFID technology lets us embed sensors into a very small chip, creating a wireless sensing device. So, we set out to develop such a single-chip versatile temperature sensor. We also wanted to be able to transfer our design to an implantable temperature sensor for an animal healthcare application with minimal structural modification. We discuss the implementation of temperature sensor. The fully integrated complementary metal-oxide semiconductor (CMOS) batteryless device measures temperature and performs calibration to compensate for the sensor's inherent imperfections. An RF link using passive RFID's backscattering technique wirelessly transmits the data to a reading device while extracting power from the same "airwave," letting the device operate anywhere and last almost forever. The entire microchip, including the temperature sensor, consumes less than a few microamperes over a half a second, so the scanning device can capture data from longer read distances.  相似文献   
975.
We describe a novel microfluidic perfusion system for high-resolution microscopes. Its modular design allows pre-coating of the coverslip surface with reagents, biomolecules, or cells. A poly(dimethylsiloxane) (PDMS) layer is cast in a special molding station, using masters made by photolithography and dry etching of silicon or by photoresist patterning on glass or silicon. This channel system can be reused while the coverslip is exchanged between experiments. As normal fluidic connectors are used, the link to external, computer-programmable syringe pumps is standardized and various fluidic channel networks can be used in the same setup. The system can house hydrogel microvalves and microelectrodes close to the imaging area to control the influx of reaction partners. We present a range of applications, including single-molecule analysis by fluorescence correlation spectroscopy (FCS), manipulation of single molecules for nanostructuring by hydrodynamic flow fields or the action of motor proteins, generation of concentration gradients, trapping and stretching of live cells using optical fibers precisely mounted in the PDMS layer, and the integration of microelectrodes for actuation and sensing.  相似文献   
976.
An attempt is made to study the Einstein relation for the diffusivity–mobility ratio (DMR) in quantum wells (QWs) and quantum well wires (QWWs) of tetragonal compounds on the basis of a newly formulated electron energy spectrum taking into account the combined influences of the anisotropies in effective electron mass, the spin–orbit splitting, and the presence of crystal field splitting, respectively. The results for quantum-confined III–V compounds form a special case of our generalized analysis. The DMR has also been studied for QWs and QWWs of II–VI and IV–VI materials. Taking QWs and QWWs of CdGeAs2, InAs, CdS and PbSe as examples, it was found that the DMR increases with increasing carrier statistics and decreasing film thickness respectively in various oscillatory manners emphasizing the influence of dimensional quantizations and the energy band constants in different cases. An experimental method of determining the DMR in nanostructures with arbitrary dispersion laws has also been suggested and the present simplified analysis is in agreement with the suggested relationship. The well-known results for nanostructures with parabolic energy bands have also been obtained as special cases from this generalized analysis under certain limiting conditions.  相似文献   
977.
A mathematical model to simulate the performance of anaerobic ponds was developed incorporating both settling of particulate components and the biological anaerobic digestion process. The biological activity includes solubilization of particulate organic matter; methanogenesis and the sulphate reduction process. The model considers that an anaerobic pond comprises a series of equal size columns. Each column has three compartments viz. liquid layer, active sediment layer and inert sediment layer. The existence of organic matter and sulphate removal mechanisms both in the bulk as well as sediment layer of the ponds and the exchange of the soluble components between the layers has been included in the model. The model was transferred to a computer program using VisSim Basic software. The model was verified by comparing simulated results with full-scale as well as with laboratory-scale anaerobic pond performance data. A good agreement between the simulated and the observed pond performance was achieved.  相似文献   
978.
Infiltration systems are frequently used as an option to manage urban storm drainage. By reducing flows and volumes in downstream sewers or in surface waters, they decrease the overflows and make it possible to recharge groundwater. They come in various forms with different uses; therefore, their performance is diverse and integrates multiple aspects. Consequently, a multicriteria approach was developed in order to quantify the performance of these systems and to help in decision making problems. For that purpose, a list of performance indicators integrating technical, economical, environmental and social aspects was developed. The performances were defined with the help of a working group composed of engineers from different technical or strategic departments from Greater Lyon and researchers from different fields. The paper presents the last version of the performance indicators tested according to a set of quality requirements: availability of data, relevance, fidelity, precision, sensitivity/robustness. This critical review of the set of indicators has led us to redefine a certain number of indicators, identify numerous biases and allow putting forward general instructions for criterion or indicator construction. The last phase is to propose multicriteria decision aid methods; a procedure using ELECTRE methods should be used.  相似文献   
979.
This article deals with directive 94/9/EC which applies to products that exist in an oil and gas company under the responsibility of the electrical, instrumentation engineers. Directive 1999/92/EC applies to users and defines the minimum requirements for improving the safety and health protection of workers, is under the responsibility of the safety division (HSE). These new ATEX directives are called the "new approach," which aims to ensure free movement of the products to which it applies by removing barriers to trade. It also aims to improve the safety of products and users. The main advantage of the new approach is that it is no longer necessary to make an adaptation to technical developments in order to keep up with technical developments  相似文献   
980.
The design principals of fast-operating electromagnetic drives with prescribed dynamic performances are examined. The represented procedure permits the command parameters to be to determined with the guaranteed prescribed parameters of the drive.  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