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   5056篇
  免费   70篇
  国内免费   3篇
电工技术   54篇
综合类   3篇
化学工业   494篇
金属工艺   41篇
机械仪表   62篇
建筑科学   102篇
矿业工程   2篇
能源动力   48篇
轻工业   316篇
水利工程   19篇
石油天然气   14篇
无线电   409篇
一般工业技术   570篇
冶金工业   2725篇
原子能技术   20篇
自动化技术   250篇
  2021年   35篇
  2020年   14篇
  2019年   25篇
  2018年   32篇
  2017年   36篇
  2016年   29篇
  2015年   31篇
  2014年   42篇
  2013年   147篇
  2012年   76篇
  2011年   115篇
  2010年   80篇
  2009年   77篇
  2008年   89篇
  2007年   99篇
  2006年   98篇
  2005年   89篇
  2004年   84篇
  2003年   89篇
  2002年   83篇
  2001年   77篇
  2000年   88篇
  1999年   118篇
  1998年   846篇
  1997年   495篇
  1996年   315篇
  1995年   215篇
  1994年   171篇
  1993年   202篇
  1992年   57篇
  1991年   68篇
  1990年   75篇
  1989年   91篇
  1988年   89篇
  1987年   69篇
  1986年   63篇
  1985年   63篇
  1984年   29篇
  1983年   39篇
  1982年   42篇
  1981年   46篇
  1980年   45篇
  1979年   30篇
  1978年   30篇
  1977年   82篇
  1976年   137篇
  1975年   26篇
  1974年   20篇
  1973年   18篇
  1972年   18篇
排序方式: 共有5129条查询结果,搜索用时 31 毫秒
1.
2.
3.
Crosstalk between microstrip transmission lines   总被引:1,自引:0,他引:1  
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk  相似文献   
4.
Lead content of rice collected from various areas in the world   总被引:1,自引:0,他引:1  
Rice samples consumed by local populations were collected between 1990 and 1995 in 17 areas in the world, mostly from Asia (10 areas), but also from 7 areas outside of Asia. In total, 1528 samples were obtained (about one half from Japan) and were analyzed for lead (Pb) by electrothermal atomic absorption spectrometry. When the Pb contents in rice samples were classified into 10 areas in Asia, the highest and the lowest geometric means (GMs) were for Indonesia (38 ng/g) and Australia (2 ng/g), respectively. Among 7 regions outside Asia, the GM was highest for Spain (58 ng/g) and the lowest for the USA. (3 ng/g). Moreover, inter-regional differences were significant, when more than 100 samples from one area were divided into 3-9 regions and GMs for regions were compared. There was a marked difference in Pb contents in rice by areas and regions in the world. Nevertheless, comparison by area of the present results with those reported in literature show that there has been no substantial reduction in Pb in rice in the past decade either in Japan or elsewhere in the world.  相似文献   
5.
We determined apolipoprotein E (ApoE) genotypes in 122 autopsied demented patients. The frequency of the ApoE epsilon 4 allele was 39.6% in Alzheimer's disease (AD), 29.0% in the Lewy body variant of AD (LBV), and 6.25% in diffuse Lewy body disease. For AD and LBV patients, the epsilon 4 frequency was significantly higher than that reported in nondemented controls (10 to 15%). Therefore, LBV and AD share ApoE epsilon 4 as a genetic risk factor, providing further evidence that these conditions overlap.  相似文献   
6.
7.
8.
A device that harnesses the mechanical energy of skeletal muscle contracting in a linear configuration has been implanted in goats. This energy convertor transforms muscle work to hydraulic energy that could drive a variety of cardiac assist devices. The device is mounted with a rib clamp and plate affixed to the sternum by cortical bone screws. A transcutaneous hydraulic line carries a silicon based working fluid to an external system that controls the muscle load. In 60 to 70 kg goats, the latissimus dorsi insertion was reattached to the energy convertor. A Telectronics myostimulator with intramuscular electrodes stimulated the latissimus dorsi. In acute implants, hydraulic pressures in excess of 150 psi were obtained. Chronic implantation of the device allowed system evaluation in the conscious unanesthetized animal. Two weeks after implant, hydraulic pressures in excess of 200 psi were obtained and energy transferred to the external loading system exceeded 1 J per contraction. Six weeks after implant, the device continued to cycle freely. These initial results are very promising and suggest an implantable energy convertor is feasible. Development of an energy convertor is an important step toward tether-free skeletal muscle powered cardiac assist devices.  相似文献   
9.
Pre-transplant nephrectomy was done in a 25-year-old man for calculous pyelonephritis using a retroperitoneal laparoscopic approach with a newly devised ligature applicator-dissector- kidney retractor.  相似文献   
10.
PURPOSE: To select ideal radiologic projections for mapping and ablation of tachycardias of right ventricular outflow tract (RVOT). METHODS: Ten hearts from human corpses were studied utilizing radiopaque material to identify the pulmonary valve and three distinct sites on this valve: septal anterior (A), septal posterior (P) and free-wall (L). Next, the hearts were filmed in the frontal plane and in oblique projections with 15 degrees increments to the right and to the left. The projections in which the sites were lateralized on the valve, eased radiologic interpretation and were considered ideal for mapping and ablation. Depending on the proximity of the sites to the lateral extremes of the pulmonary valve, the projections were considered ideal ( ), intermediary (++) and inadequate (+). RESULTS: Projections [table: see text] CONCLUSION: The A site of RVOT was best indicated in the 60 and 45 degrees left anterior oblique projections; the 0 degree postero anterior projection was best for mapping the P site; the L region was best explored in the 60 degrees right anterior oblique projection.  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