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   569042篇
  免费   6347篇
  国内免费   1005篇
电工技术   10533篇
综合类   467篇
化学工业   90628篇
金属工艺   23376篇
机械仪表   18551篇
建筑科学   12598篇
矿业工程   4314篇
能源动力   14523篇
轻工业   45913篇
水利工程   6949篇
石油天然气   14965篇
武器工业   39篇
无线电   60527篇
一般工业技术   116675篇
冶金工业   95659篇
原子能技术   14692篇
自动化技术   45985篇
  2021年   5542篇
  2020年   4066篇
  2019年   5320篇
  2018年   9265篇
  2017年   9463篇
  2016年   9918篇
  2015年   6085篇
  2014年   10338篇
  2013年   26269篇
  2012年   15945篇
  2011年   21298篇
  2010年   17135篇
  2009年   18957篇
  2008年   19208篇
  2007年   18911篇
  2006年   16387篇
  2005年   14825篇
  2004年   14071篇
  2003年   13740篇
  2002年   13294篇
  2001年   12894篇
  2000年   12361篇
  1999年   12048篇
  1998年   27694篇
  1997年   20069篇
  1996年   15646篇
  1995年   12019篇
  1994年   10871篇
  1993年   10627篇
  1992年   8351篇
  1991年   8112篇
  1990年   7998篇
  1989年   7768篇
  1988年   7482篇
  1987年   6756篇
  1986年   6538篇
  1985年   7392篇
  1984年   6703篇
  1983年   6441篇
  1982年   5779篇
  1981年   5896篇
  1980年   5630篇
  1979年   5734篇
  1978年   5665篇
  1977年   6181篇
  1976年   7688篇
  1975年   5109篇
  1974年   4903篇
  1973年   4980篇
  1972年   4279篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
123.
Contents     
This article explains the basic issues that are facing the global community regarding the emission of carbon dioxide (CO/sub 2/) gas that is degrading our environment and, most significantly, the environment of generations to come. This article deals with the current state of a potential international agreement to curtail greenhouse gases and the subsequent underlying issues. A theory suggests that apparent reluctance to agree to an international treaty by the United States is directly tied to the process of electric utility reforms. The proposed Kyoto Treaty is explained as well as the consequences of its implementation. The current facts surrounding electric utility generation and CO/sub 2/ gas emissions are explained, as are some mitigation efforts.  相似文献   
124.
High-performance Y-branch digital optical switches realized in Ti:LiNbO3 are presented. Their switching response functions have been optimized in terms of switch voltage and crosstalk ratio. The optimization is based on analyzing different types of waveguide shaping and switching arrangements using coupled mode theory and computer simulations. Excellent switching characteristics are achieved with devices exploiting a specially shaped waveguide branch in a dilated switch arrangement. Demonstrated performances include switching voltage as low as 9 V with crosstalk suppression better than 45 dB and fiber-to-fiber losses as low as 4 dB. Polarization independence with crosstalk suppression better than 40 dB over a 1520- to 1570-nm wavelength range is achieved for any applied switch voltage greater than 18 V. These optimized digital optical switches have further demonstrated the capability to reshape electrical input signals at switching rates of several hundred megahertz  相似文献   
125.
126.
A mixed K-value model allows existing computer programs for the simulation of vapor-liquid equilibrium stages to be used for three-phase vapor-liquid-liquid systems. The mixed K-value model has been implemented with a minimum effort into the Badger General Material Balance flow-sheeting program. Good convergence has been obtained with the mixed K-value model for a number of systems. A comparison is made with published literature [1, 2], showing excellent results with this generally applicable and easy-to-use method.  相似文献   
127.
A short recipe for seashell synthesis   总被引:2,自引:0,他引:2  
Several artistic examples of seashell-like forms produced on a graphics supercomputer are provided. The shapes were created using a simple graphics primitive and rendered using lighting and shading facilities of 3-D extensions to X Windows or the PHIGS+ proposed standard. It is expected that the techniques, equations, and systems will provide useful tools and stimulate future studies in the graphics characterization of morphologically rich spiral shapes produced by relatively simple generating formulas  相似文献   
128.
Tomijima  A.U. 《Software, IEEE》1987,4(1):17-21
Japan rejected a proposal to adopt a special software protection law and instead modified its copyright law to include software. This change may affect US firms doing business there.  相似文献   
129.
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   
130.
Incremental transmission loss analysis has been used for decades, but recent interest in its application to loss allocation calls for new in-depth results. This paper demonstrates that, for incremental methods to be applied correctly in loss allocation, it is first necessary to specify the load distribution and loss supply strategies. Incremental loss allocation among bus power injections is shown to be arbitrary and, therefore, open to challenge as discriminatory. Loss allocation is possible among incremental loads and/or generators, but the proportion of the total losses assigned to either one is arbitrary. Unique, nonarbitrary incremental loss allocations are however possible among the "equivalent" incremental bilateral exchanges between generators and loads. From these basic components it is possible then to calculate the allocation among generators or loads in any specified proportion. The main results, although developed initially for small increments, are extended to large variations. Finally, a general incremental loss allocation algorithm is developed and tested  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