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   378578篇
  免费   7002篇
  国内免费   2254篇
电工技术   6427篇
技术理论   5篇
综合类   3478篇
化学工业   59482篇
金属工艺   16272篇
机械仪表   11445篇
建筑科学   9908篇
矿业工程   2273篇
能源动力   7431篇
轻工业   33791篇
水利工程   4410篇
石油天然气   6477篇
武器工业   247篇
无线电   39208篇
一般工业技术   70976篇
冶金工业   59836篇
原子能技术   6055篇
自动化技术   50113篇
  2021年   3285篇
  2020年   2346篇
  2019年   2762篇
  2018年   18464篇
  2017年   17357篇
  2016年   14522篇
  2015年   4351篇
  2014年   6065篇
  2013年   14081篇
  2012年   12736篇
  2011年   20940篇
  2010年   17418篇
  2009年   15238篇
  2008年   17444篇
  2007年   18286篇
  2006年   9651篇
  2005年   9441篇
  2004年   8636篇
  2003年   8128篇
  2002年   7428篇
  2001年   6872篇
  2000年   6541篇
  1999年   6542篇
  1998年   16043篇
  1997年   11445篇
  1996年   8549篇
  1995年   6294篇
  1994年   5772篇
  1993年   5624篇
  1992年   4213篇
  1991年   4030篇
  1990年   4086篇
  1989年   4012篇
  1988年   3763篇
  1987年   3228篇
  1986年   3268篇
  1985年   3657篇
  1984年   3532篇
  1983年   3236篇
  1982年   2896篇
  1981年   3102篇
  1980年   2826篇
  1979年   3003篇
  1978年   2878篇
  1977年   3069篇
  1976年   4181篇
  1975年   2574篇
  1974年   2391篇
  1973年   2419篇
  1972年   2034篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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   
52.
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   
53.
54.
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   
55.
56.
57.
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General Motors Corporation is reviewed.  相似文献   
58.
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated by using the proposed procedure.  相似文献   
59.
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   
60.
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