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   252630篇
  免费   3030篇
  国内免费   867篇
电工技术   4807篇
综合类   193篇
化学工业   36120篇
金属工艺   9506篇
机械仪表   7545篇
建筑科学   6072篇
矿业工程   880篇
能源动力   7227篇
轻工业   21093篇
水利工程   2202篇
石油天然气   3230篇
武器工业   15篇
无线电   34285篇
一般工业技术   49975篇
冶金工业   48546篇
原子能技术   5077篇
自动化技术   19754篇
  2021年   2169篇
  2020年   1561篇
  2019年   1915篇
  2018年   3272篇
  2017年   3308篇
  2016年   3401篇
  2015年   2217篇
  2014年   3955篇
  2013年   11477篇
  2012年   6234篇
  2011年   8574篇
  2010年   6904篇
  2009年   7884篇
  2008年   8403篇
  2007年   8298篇
  2006年   7363篇
  2005年   6497篇
  2004年   6283篇
  2003年   6555篇
  2002年   6036篇
  2001年   6514篇
  2000年   5975篇
  1999年   6392篇
  1998年   16484篇
  1997年   11410篇
  1996年   8796篇
  1995年   6606篇
  1994年   5901篇
  1993年   5842篇
  1992年   4131篇
  1991年   4020篇
  1990年   3857篇
  1989年   3648篇
  1988年   3560篇
  1987年   3018篇
  1986年   2942篇
  1985年   3206篇
  1984年   2926篇
  1983年   2828篇
  1982年   2636篇
  1981年   2542篇
  1980年   2461篇
  1979年   2305篇
  1978年   2107篇
  1977年   2604篇
  1976年   3562篇
  1975年   1764篇
  1974年   1729篇
  1973年   1665篇
  1972年   1465篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
281.
Increasing attention at oil refineries is being focused on solving environmental problems caused by stiffening of the requirements for emissions of harmful substances into air and water. Advanced technologies that reduce the effect of industrial enterprises on the environment to the minimum are becoming increasingly in demand. Treatment of process wastewaters to remove hydrogen sulfide and ammonia is one such problem of the modern refinery with cat crackers. __________ Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 3, pp. 52–55, May–June, 2006.  相似文献   
282.
Several coats, such as gray cast iron, cast iron alloyed with nickel and copper, nickel-aluminum, Nichrome (nickel-chromium alloy), bronze, etc., have been investigated. Corrosion resistance of coats in a medium based on drilling mud and sodium chloride and sulfate solutions has been checked. Alloyed cast iron admixed with tin-based compounds showed the best results. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 3, pp. 43–44, March, 2006.  相似文献   
283.
In this paper, we propose low-power designs for the synchronizer and channel estimator units of the Inner Receiver in wireless local area network systems. The objective of the work is the optimization, with respect to power, area, and latency, of both the signal processing algorithms themselves and their implementation. Novel circuit design strategies have been employed to realize optimal hardware and power efficient architectures for the fast Fourier transform, arc tangent computation unit, numerically controlled oscillator, and the decimation filters. The use of multiple clock domains and clock gating reduces the power consumption further. These blocks have been integrated into an experimental digital baseband processor for the IEEE 802.11a standard implemented in the 0.25mum- 5-metal layer BiCMOS technology from Institute for High Performance Microelectronics.  相似文献   
284.
Network performance engineering can verify the design and dimensioning of large-scale control networks like CSMA-based building automation networks. It combines performance analysis with diagnosis methods to evaluate the network utilization and to detect design errors before installation and can therewith save the expenses of overdimensioning and redesign. This paper will develop a diagnosis model based on fault trees that is able to use the huge amount of performance analysis results to identify design errors and analyze their coherences. This enables not only a fast tracing back of fault causes and the derivation of solutions; it can also visualize the fault coherence to the user and help him to understand his design. Additional consulting tools implement best practice strategies, to support the user in parameterization.  相似文献   
285.
A 0.9 V 92 dB Double-Sampled Switched-RC Delta-Sigma Audio ADC   总被引:1,自引:0,他引:1  
A 0.9 V third-order double-sampled delta-sigma audio ADC is presented. A new method using a combination of a switched-RC technique and a floating switched-capacitor double-sampling configuration enabled low-voltage operation without clock boosting or bootstrapping. A three-level quantizer with simple dynamic element matching was used to improve linearity. The prototype IC implemented in a 0.13 CMOS process achieves 92 dB DR, 91 dB SNR and 89 dB SNDR in a 24 kHz audio signal bandwidth, while consuming 1.5 mW from a 0.9 V supply. The prototype operates from 0.65 V to 1.5 V supply with minimal performance degradation.  相似文献   
286.
Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability.  相似文献   
287.
This paper deals with accurate recipe implementation for abnormal condition management in a batch process using a case‐based reasoning (CBR) approach. A set of new problems can be solved by reusing proven process solutions. The proposed system integrates quantitative and qualitative parameters for adaptation of cases. A novel methodology to generate accurate recipes and to adapt to the processes is introduced during normal and abnormal conditions. In particular, the differences between current conditions and the references (recipes) should be managed to prevent any hazardous conditions arising. The processes are evaluated using their similarity to the past cases. This intelligent approach distinguishes plausible cases, generates accurate recipes, and adapts to new situations. The aim is to use the offline historical process data and safety related information in order to propose changes and adjustments in the processes.  相似文献   
288.
A new supported liquid membrane (SLM) system was prepared for the selective transport of bismuth ions from the aqueous feed into the aqueous permeate phase. The support of the SLM was a thin porous polypropylene or polyvinylidene fluoride membrane impregnated with diisooctyldithiophosphinic acid (Cyanex 301) as mobile carrier in 4‐chloroacetophenon as organic solvent. Cyanex 301 acts as a highly selective carrier for the uphill transport of bismuth ions through the SLM. In the presence of HNO3 as a metal ion acceptor in the strip solution, the transport of bismuth ions into the strip side reached 70 % of the initial feed concentration after 3.5 hours. The selectivity and efficiency of bismuth transport from aqueous solutions containing different mixtures of cations were investigated. In the presence of P2O72– ions as suitable masking agent in the feed solution, the interfering effects of other cations were completely eliminated. The selective transport of bismuth through SLM is superior to liquid‐liquid extraction or through bulk liquid membranes. This is due to the high efficiency. The SLM reduces the solvent requirements, combines extraction and stripping operations in a single process and allows the use of highly selective extractants. The system may be applied to samples containing very low bismuth concentrations.  相似文献   
289.
290.
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