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   523925篇
  免费   7433篇
  国内免费   2421篇
电工技术   10707篇
技术理论   5篇
综合类   1714篇
化学工业   81608篇
金属工艺   19877篇
机械仪表   15157篇
建筑科学   13493篇
矿业工程   2438篇
能源动力   13050篇
轻工业   50030篇
水利工程   5015篇
石油天然气   9051篇
武器工业   250篇
无线电   61117篇
一般工业技术   98648篇
冶金工业   96970篇
原子能技术   9968篇
自动化技术   44681篇
  2021年   4387篇
  2019年   3902篇
  2018年   6433篇
  2017年   6233篇
  2016年   6681篇
  2015年   4988篇
  2014年   8289篇
  2013年   23798篇
  2012年   13827篇
  2011年   18711篇
  2010年   14808篇
  2009年   16392篇
  2008年   17516篇
  2007年   17534篇
  2006年   15520篇
  2005年   13961篇
  2004年   13092篇
  2003年   12583篇
  2002年   12362篇
  2001年   12590篇
  2000年   11881篇
  1999年   12246篇
  1998年   28095篇
  1997年   20583篇
  1996年   16043篇
  1995年   12277篇
  1994年   11287篇
  1993年   10864篇
  1992年   8404篇
  1991年   7987篇
  1990年   7986篇
  1989年   7791篇
  1988年   7492篇
  1987年   6313篇
  1986年   6510篇
  1985年   7391篇
  1984年   6949篇
  1983年   6490篇
  1982年   5797篇
  1981年   6124篇
  1980年   5630篇
  1979年   5752篇
  1978年   5471篇
  1977年   6153篇
  1976年   7994篇
  1975年   4803篇
  1974年   4535篇
  1973年   4630篇
  1972年   3887篇
  1971年   3453篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Poiseuille, known for his law of fluid flow, which is the analog of Ohm's law, introduced the units (mmHg) by which we measure blood pressure by using the mercury manometer, which he described in his medical school thesis in 1828. For 50 years, mean blood pressure was all that could be measured because of the long response time of the mercury manometer. It is true that the height of the mercury column displayed pulsatile oscillations, but their amplitude was much less than that of pulse pressure. It is interesting to note that the slowly responding mercury manometer was made to display first systolic then diastolic pressure by means of an ingenious device that contained two oppositely directed check valves. It took from 1828 to 1903 for high-fidelity graphic recordings of blood pressure to appear in which systolic and diastolic pressures were believable. However, systolic and diastolic pressures were measurable since 1878 when Golz and Gaule created their ingenious valved device that permitted use of the slowly responding mercury manometer to display these pressures accurately  相似文献   
112.
It is essential in the simulation of power electronics applications to model magnetic components accurately. In addition to modeling the nonlinear hysteresis behavior, eddy currents and winding losses must be included to provide a realistic model. In practice the losses in magnetic components give rise to significant temperature increases which can lead to major changes in the component behavior. In this paper a model of magnetic components is presented which integrates a nonlinear model of hysteresis, electro-magnetic windings and thermal behavior in a single model for use in circuit simulation of power electronics systems. Measurements and simulations are presented which demonstrate the accuracy of the approach for the electrical, magnetic and thermal domains across a variety of operating conditions, including static thermal conditions and dynamic self heating  相似文献   
113.
Front Cover     
In this paper, the authors present the results of experiments which clearly demonstrate a technical basis confirming that the carrier frequency harmonics data can be used for diagnostics relative to motor stator insulation degradation.  相似文献   
114.
巴西的一个重要电力公司COPEL最近开发了一个水电站高级控制系统,这是在电力部门经受重大变革时期,提高水电竞争力的里程碑。  相似文献   
115.
116.
The kinetics of changes in the bound water content in dietetic sucrose-free sponge cakes (DC) during storage was investigated. The effect of edible films of polymyxan, pectin, xanthan, and carboxymethylcellulose upon this kinetics was also investigated. The quantitative changes in both states of water (slightly bound water and strongly bound water) were registered by combined dynamic analysis (thermogravimetry analysis, TGA, and differential thermal analysis, DTA). The moisture changes in DC crumb were analyzed by drying out to constant mass. The rate constants were determined according the equation q = qoe-kt. The values of rate constants 'k', in day-1, concerning the different edible films were as follows: for crumb moisture is (8.00 ≤ k ≤ 12.47) × 10-3, for bound water is (3.07 ≤ kw ≤ 6.26) × 10-2, for slightly bound water is (4.22 ≤ k1 ≤ 8.49) × 10-2 and for strongly bound water is (2.02 ≤ k2 ≤ 5.62) × 10-2 as compared to 18.53 × 10-3, 7.16 × 10-2, 9.04 × 10-2, and 5.36 × 10-2 in the uncovered DC, respectively. The best water-retaining effect in respect to crumb moisture during storage was ascertained in the use of polymyxan and xanthan films. The lowest rate constant values for bound water and its two states were measured for DC covered with pectin. The relation between the kinetics of both bound water states during storage and ageing of the crumb of DC covered with different edible films and the crumb microstructure was represented. By means of scanning electron microscope was read the smallest change in crumb microstructure of pectin-covered DC on the sixth day of storage.  相似文献   
117.
118.
It is established that the capillary rise of a liquid has an oscillatory character, in contrast to the commonly accepted opinion that a vertical capillary is filled at a monotonically varying velocity. The value of the tangential shear stress arising in an ascending liquid is evaluated for ethyl alcohol and distilled water.  相似文献   
119.
A method for assessing health care technology that models the demand on the clinician's attention exerted by patients' data (diagnostic and therapeutic) can provide a means for simultaneously reducing the cost and improving the quality of health care. The attentional demand exerted by patients' data can be measured by the amount of uncertainty in the data. Uncertainty can be expressed mathematically by the concept of entropy in information theory.  相似文献   
120.
In temperate seas such as the North Sea harmful (toxic) algal blooms will probably increase as a result of climate change. This conclusion was reached after investigating the projected effect of climate change for the year 2100 in Dutch coastal waters (4 degrees C temperature rise and increased water column stratification) on the growth rates of six harmful and two non-harmful phytoplankton species. Micro algae form the basis of the marine food chain. However, toxin-producing species may seriously disrupt the food web and lead to fish kills and human intoxication. Two species with estimated doubled growth rates in 2100, F. japonica and C. antiqua, entered Europe via ship's ballast water or shellfish imports. This stresses the need to legally regulate such invasion routes in order to prevent the import of novel species. Future toxic phytoplankton blooms may further devaluate ecosystem deliverables such as fish production or recreational use. This devaluation can be estimated by monetary value assessments that are needed in cost-benefit analyses for policy guidance. The lack of understanding of future climate, ecosystem functioning and its response to climate change calls for a scientific effort to improve our knowledge on present day coastal ecosystem functioning and its resilience.  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