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   20277篇
  免费   991篇
  国内免费   138篇
电工技术   335篇
综合类   33篇
化学工业   4492篇
金属工艺   609篇
机械仪表   692篇
建筑科学   401篇
矿业工程   49篇
能源动力   1430篇
轻工业   1220篇
水利工程   222篇
石油天然气   85篇
武器工业   1篇
无线电   2523篇
一般工业技术   4584篇
冶金工业   1590篇
原子能技术   185篇
自动化技术   2955篇
  2024年   79篇
  2023年   430篇
  2022年   980篇
  2021年   1184篇
  2020年   942篇
  2019年   974篇
  2018年   1253篇
  2017年   1003篇
  2016年   962篇
  2015年   634篇
  2014年   876篇
  2013年   1660篇
  2012年   942篇
  2011年   1139篇
  2010年   925篇
  2009年   858篇
  2008年   763篇
  2007年   618篇
  2006年   515篇
  2005年   395篇
  2004年   293篇
  2003年   263篇
  2002年   204篇
  2001年   187篇
  2000年   191篇
  1999年   195篇
  1998年   319篇
  1997年   271篇
  1996年   245篇
  1995年   190篇
  1994年   187篇
  1993年   178篇
  1992年   124篇
  1991年   157篇
  1990年   112篇
  1989年   115篇
  1988年   97篇
  1987年   107篇
  1986年   89篇
  1985年   110篇
  1984年   98篇
  1983年   83篇
  1982年   69篇
  1981年   79篇
  1980年   58篇
  1979年   37篇
  1978年   36篇
  1977年   33篇
  1976年   43篇
  1975年   18篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
71.
Clean Technologies and Environmental Policy - Manufacturing organizations are under continuous pressure to implement sustainability in their activities. There is a need to identify the...  相似文献   
72.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer. But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that, the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic whereas chloride doped polyaniline films were found to be highly hygroscopic.  相似文献   
73.
Attribute Allocation and Retrieval Scheme for Large-Scale Sensor Networks   总被引:1,自引:0,他引:1  
Wireless sensor network is an emerging technology that enables remote monitoring of large geographical regions. In this paper, we address the problem of distributing attributes over such a large-scale sensor network so that the cost of data retrieval is minimized. The proposed scheme is a data-centric storage scheme where the attributes are distributed over the network depending on the correlations between them. The problem addressed here is similar to the Allocation Problem of distributed databases. In this paper, we have defined the Allocation Problem in the context of sensor networks and have proposed a scheme for finding a good distribution of attributes to the sensor network. We also propose an architecture for query processing given such a distribution of attributes. We analytically determine the conditions under which the proposed architecture is beneficial and present simulation results to demonstrate the same. To the best of our knowledge, this is the first attempt to determine an allocation of attributes over a sensor network based on the correlations between attributes.  相似文献   
74.
75.
The paper is a comprehensive review of the Spanish National Hydrological Plan, which proposes to transfer water from the lower part of the Ebro River up to the Levante basins, around 912 km away. The National Hydrological Plan is a conventional, static plan, which focuses primarily on supply management. The plan is based on the explicit assumption that the world will change only incrementally during its entire economic life of 100-200 years. The analysis indicates that much of the increased water demands forecasted are unlikely to materialize due to increasing emphasis on demand management practices, major structural changes in the agricultural sector that will occur by 2020 and the requirements of the Water Directive of the European Union, which must be fulfilled by 2010. Even now, the cost per cubic metre of water delivered at the end of the transfer is nearly twice the cost of desalinated water. The National Hydrological Plan in its present form cannot be justified for economic, environmental and social reasons. In addition, the plan will not be necessary if demand management practices are implemented.  相似文献   
76.
77.
Mobile wireless sensor networks (MWSNs) will enable information systems to gather detailed information about the environment on an unprecedented scale. These self‐organizing, distributed networks of sensors, processors, and actuators that are capable of movement have a broad range of potential applications, including military reconnaissance, surveillance, planetary exploration, and geophysical mapping. In many of the foreseen applications, the MWSN will need to form a geometric pattern without assistance from the user. In military reconnaissance, for example, the nodes will be dropped onto the battlefield from a plane and land at random positions. The nodes will be expected to arrange themselves into a predetermined formation in order to perform a specific task. Thus, we present algorithms for forming a line, circle, and regular polygon from a given set of random positions. The algorithms are distributed and use no communication between the nodes to minimize energy consumption. Unlike past studies of geometric problems where algorithms are either tested in simulations where each node has global knowledge of all the other nodes or implemented on a small number of robots, the robustness of our algorithms has been studied with simulations that model the sensor system in detail. The simulations demonstrate that the algorithms are robust against random errors in the sensors and actuators. © 2004 Wiley Periodicals, Inc.  相似文献   
78.
The supply voltage to threshold voltage ratio is reduced with each new technology generation. The gate overdrive variation with temperature plays an increasingly important role in determining the speed characteristics of CMOS integrated circuits. The temperature-dependent propagation delay characteristics, as shown in this brief, will experience a complete reversal in the near future. Contrary to the older technology generations, the speed of circuits in a 45-nm CMOS technology is enhanced when the temperature is increased at the nominal supply voltage. Operating an integrated circuit at the prescribed nominal supply voltage is not preferable for reliable operation under temperature fluctuations. A design methodology based on optimizing the supply voltage for temperature-variation-insensitive circuit performance is proposed in this brief. The optimum supply voltage is 45% to 53% lower than the nominal supply voltage in a 180-nm CMOS technology. Alternatively, the optimum supply voltage is 15% to 35% higher than the nominal supply voltage in a 45-nm CMOS technology. The speed and energy tradeoffs in the supply voltage optimization technique are also presented  相似文献   
79.
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication.  相似文献   
80.
A mismatch between demand and supply for bandwidth is common in transport carrier networks. This mismatch is generally a result of the disparity between a carrier's capacity buildout and its anticipated customer demand. A carrier with temporary bandwidth deficit or lack of presence in a geographical region and a carrier with surplus capacity in the right locations can be brought together by the emerging bandwidth exchange technology. Bandwidth exchange offers a win-win solution, in which the carrier with a deficit avoids losing revenue by buying capacity from the carrier with surplus, and the latter makes additional revenue by retail sale of its excess capacity. While the concept of real-time purchase and exchange of bandwidth has attracted a lot of attention, many technical challenges stand in the way of making it a reality. The purpose of this article is to provide an engineering framework for enabling real-time bandwidth exchange with committed quality of service and service level agreement among transport carriers. Special emphasis is given to identifying the architectural requirements and the enabling infrastructure necessary for building a viable bandwidth exchange that can be used for creating revenue out of surplus stranded capacity. Indepth analysis of cross-carrier service level agreement specification, capacity publication, route design, and service provisioning are also provided in the article.  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