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   2451篇
  免费   59篇
  国内免费   6篇
电工技术   16篇
综合类   1篇
化学工业   448篇
金属工艺   49篇
机械仪表   51篇
建筑科学   117篇
矿业工程   7篇
能源动力   48篇
轻工业   208篇
水利工程   35篇
石油天然气   1篇
无线电   264篇
一般工业技术   381篇
冶金工业   580篇
原子能技术   17篇
自动化技术   293篇
  2021年   23篇
  2020年   19篇
  2019年   27篇
  2018年   32篇
  2017年   26篇
  2016年   51篇
  2015年   26篇
  2014年   49篇
  2013年   116篇
  2012年   78篇
  2011年   139篇
  2010年   80篇
  2009年   81篇
  2008年   105篇
  2007年   108篇
  2006年   104篇
  2005年   110篇
  2004年   78篇
  2003年   66篇
  2002年   70篇
  2001年   58篇
  2000年   50篇
  1999年   55篇
  1998年   106篇
  1997年   69篇
  1996年   73篇
  1995年   44篇
  1994年   46篇
  1993年   31篇
  1992年   34篇
  1991年   22篇
  1990年   34篇
  1989年   37篇
  1988年   34篇
  1987年   27篇
  1986年   32篇
  1985年   43篇
  1984年   34篇
  1983年   36篇
  1982年   27篇
  1981年   21篇
  1980年   18篇
  1979年   17篇
  1978年   23篇
  1977年   19篇
  1976年   22篇
  1975年   23篇
  1974年   20篇
  1973年   15篇
  1971年   11篇
排序方式: 共有2516条查询结果,搜索用时 15 毫秒
21.
A few years ago, Sun Microsystems CEO Scott McNealy created uproar by declaring: ‘You have zero privacy. Get over it.’ ( Sprenger, 1999 ) The question, at least for Americans, is did the 11 September terrorist attacks – and the response to them – prove him right? Is privacy really dead?  相似文献   
22.
Three methods approved by the National Committee for Clinical Laboratory Standards for testing the susceptibility of anaerobic bacteria were used to evaluate the fluoroquinolone, trovafloxacin. The methods gave essentially comparable results with 126 anaerobes and with three quality control strains. A collaborative study defined the quality control range for trovafloxacin MICs. Trovafloxacin had good in vitro activity against the more common anaerobes (MIC 90 < = or 2.0 micrograms/ml).  相似文献   
23.
The intensity and frequency chirp of picosecond pulses from a self-seeded gain-switched Fabry-Perot laser diode have been directly measured using the technique of frequency-resolved optical gating. Measurements over an output sidemode suppression ratio (SMSR) range of 15-35 dB show that higher SMSR's are associated with an increasingly linear frequency chirp across the output pulses. This complete pulse characterization allows the conditions for optimum pulse compression to be determined accurately, and indicates that transform-limited, pedestal free pulses can be obtained at an SMSR of 35 dB  相似文献   
24.
The morphology of surfaces of several ceramic materials has been examined using transmission electron microscopy. The approach used was to prepare a sample for examination in the microscope, carefully clean it, and then heat-treat it. In the case of the oxides studied (alumina and spinel) the samples were heated in air; the non-oxides (α-SiC and β -SiC) were annealed under vacuum. The morphology in all but one case was such that the surface faceted parallel to the nearest low-index plane to give well-defined terraces; these were separated by ledges which also tended to facet parallel to the traces of low-index planes. The exception was the {1100} alumina surface, which appears to be unstable in air at temperatures close to 1400°C. A computer program using a multislice approach was used to estimate the height of the steps on the (0001) surface; the step heights appear to be multiples of the c lattice parameter. A reconstruction of this surface as a result of this heat treatment is also proposed.  相似文献   
25.
Corrosion-related failures in electric power plants often stimulate research aimed at understanding the cause of the failures and at developing cost-effective corrosion control options. This paper describes some of the success stories. Over the last few years, EPRI has helped solve several aqueous corrosion problems using the following approaches: materials selection, coatings, water chemistry control, residual stress modification and corrosion monitoring. These approaches were applied successfully to flue gas desulfurization systems, low pressure steam turbines and boiling water reactor piping. A measure of the success of these corrosion control options is the cost savings of over $570 million documented by only seven of EPRI's over 700 utility members after applying these techniques.  相似文献   
26.
27.
28.
Barry  R.A. 《Electronics letters》1993,29(14):1252-1254
All-optical networks without switches are considered where the signals are routed based on wavelength only. 2 square root (M log/sub 2/( square root (2)M)) wavelengths are shown to be sufficient to build an M*M nonblocking connector without switches and without wavelength changers.<>  相似文献   
29.
The prospects for rapid near-term development of a synfuel industry in the USA have decreased, due to depressed world oil prices, synfuel project cost overruns, and the lukewarm support of the Reagan administration. Nonetheless, socioeconomic and environmental impact analysis studies can provide valuable information for determining the regional welfare effects of proposed projects. The author discusses the results of a regional econometric analysis of the synfuel projects planned for Western Kentucky, which focuses on environmental impacts, and reveals the inevitable trade-offs that would accompany synfuel development. Some policy issues are briefly reviewed, especially that of efficient energy pricing.  相似文献   
30.
Growth and voluntary feed intake (VFI) in grazing temperate farmed deer species are influenced by the feeding value of the forage and the stage of the deer's seasonal cycle. Liveweight gain (LWG) of growing red deer was greater when perennial ryegrass (0.80)/white clover (0.20) pasture was grazed at 10 cm than 5 cm surface height, but venison production by one year of age was still low. Chicory and red clover were of superior feeding value for deer than perennial ryegrass-based pastures, increasing LWG of young red and hybrid (0.25 elk; 0.75 red deer) deer during summer and autumn, due to higher VFI and to higher organic matter digestibility. Relative to perennial ryegrass, chicory disintegrated faster in the rumen, with very low rumination time and faster rumen outflow rates of liquid and particulate matter. Inputs of red clover and chicory substantially increased venison carcass weights at one year of age from grazing red and hybrid stags. In indoor pen feeding studies, red deer were shown to have a seasonal cycle of digestive function, with greater rumen mean retention time (MRT) and greater rates of rumen ammonia production in summer than in winter. It was deduced that the purpose of the digestive cycle was to maintain apparent digestibility constant as VFI increased during summer. Tropical sambar deer were also shown to have seasonal cycles in growth and VFI that were of reduced amplitude compared with red deer. Peak VFI and growth occurred in autumn and minimum VFI and growth occurred in spring. Feed conversion (kg DM eaten/kg LWG) was more efficient for sambar than for red deer, due to lower VFI and lower heat production, but there was no difference between species in digestive efficiency.  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