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   264808篇
  免费   4457篇
  国内免费   1823篇
电工技术   5470篇
技术理论   5篇
综合类   1164篇
化学工业   43275篇
金属工艺   11149篇
机械仪表   7811篇
建筑科学   6682篇
矿业工程   1672篇
能源动力   5712篇
轻工业   26295篇
水利工程   2899篇
石油天然气   6006篇
武器工业   243篇
无线电   27865篇
一般工业技术   49760篇
冶金工业   48179篇
原子能技术   5634篇
自动化技术   21267篇
  2021年   2743篇
  2019年   2198篇
  2018年   3531篇
  2017年   3499篇
  2016年   3835篇
  2015年   2914篇
  2014年   4727篇
  2013年   11598篇
  2012年   7851篇
  2011年   10397篇
  2010年   8255篇
  2009年   8788篇
  2008年   9584篇
  2007年   9703篇
  2006年   8499篇
  2005年   7443篇
  2004年   6717篇
  2003年   6250篇
  2002年   6252篇
  2001年   6341篇
  2000年   5932篇
  1999年   5898篇
  1998年   13024篇
  1997年   9720篇
  1996年   7403篇
  1995年   5615篇
  1994年   5121篇
  1993年   5009篇
  1992年   3957篇
  1991年   3762篇
  1990年   3841篇
  1989年   3787篇
  1988年   3546篇
  1987年   3033篇
  1986年   3062篇
  1985年   3426篇
  1984年   3351篇
  1983年   3096篇
  1982年   2739篇
  1981年   2944篇
  1980年   2696篇
  1979年   2866篇
  1978年   2773篇
  1977年   2945篇
  1976年   3907篇
  1975年   2471篇
  1974年   2296篇
  1973年   2331篇
  1972年   1988篇
  1971年   1787篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
41.
Lenin Dnepropetrovsk Pipe Plant. Translated from Metallurg, No. 8, p. 39, August, 1989.  相似文献   
42.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed.  相似文献   
43.
44.
We consider three types of near-boundary elements: curvilinear quadrangles and families of arcs and points, and their application to a two-dimensional problem of the static theory of elasticity with boundary conditions in displacements. The comparison of the theoretical and numerical aspects of the obtained solutions is performed. It is shown that the accuracy of evaluation of the components of the vector of displacements increases in the following cases: in the case of complete quantization of the near-boundary region (but not in the case of its partial quantization or quantization with overlapping), in the case where the numbers of arcs and points increase, and in the case of simultaneous application of different types of near-boundary elements (specifically, quadrangles and families of arcs).  相似文献   
45.
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   
46.
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   
47.
48.
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   
49.
50.
Summary The effect of the addition of four commercial pectolytic preparations on the visual characteristics (colour and turbidity) of red wines has been evaluated. The effect of both clarifying and colour extracting enzymes and the effect of different doses used, were evaluated and compared. All the red wines treated enzymatically, independent of the type of enzyme and dose, present chromatic characteristics which can be considered better than those of the control wines. Also, those wines treated with enzymes had greater stability during 2 years storage in bottles, in particular the turbidity was better than untreated wines.  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