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   542373篇
  免费   7363篇
  国内免费   1831篇
电工技术   10054篇
综合类   434篇
化学工业   82051篇
金属工艺   20029篇
机械仪表   15552篇
建筑科学   14880篇
矿业工程   1670篇
能源动力   14446篇
轻工业   54205篇
水利工程   4662篇
石油天然气   4748篇
武器工业   14篇
无线电   68564篇
一般工业技术   100312篇
冶金工业   101957篇
原子能技术   8929篇
自动化技术   49060篇
  2021年   3665篇
  2019年   3373篇
  2018年   5390篇
  2017年   5505篇
  2016年   5848篇
  2015年   4597篇
  2014年   7628篇
  2013年   24854篇
  2012年   13369篇
  2011年   19096篇
  2010年   14849篇
  2009年   17009篇
  2008年   17889篇
  2007年   18314篇
  2006年   16190篇
  2005年   15099篇
  2004年   14639篇
  2003年   14180篇
  2002年   13743篇
  2001年   13811篇
  2000年   12898篇
  1999年   13528篇
  1998年   31878篇
  1997年   23137篇
  1996年   18095篇
  1995年   14053篇
  1994年   12354篇
  1993年   12002篇
  1992年   8960篇
  1991年   8565篇
  1990年   8145篇
  1989年   7909篇
  1988年   7590篇
  1987年   6509篇
  1986年   6417篇
  1985年   7740篇
  1984年   7192篇
  1983年   6385篇
  1982年   5974篇
  1981年   5951篇
  1980年   5595篇
  1979年   5486篇
  1978年   5141篇
  1977年   6227篇
  1976年   8311篇
  1975年   4373篇
  1974年   4259篇
  1973年   4202篇
  1972年   3436篇
  1971年   3075篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
This study employed two perspectives to investigate media attention given women congressional candidates. The first perspective is that media attention may be explained by typical and normal media processes, such as focusing on incumbents. The second perspective considers a partisan explanation in which media attention is weighted more to Democratic candidates than Republican candidates. This study employs two established sources, Vanderbilt's Television News Index and Abstract and Information Access's National Newspaper Index , to examine the national media attention of Democratic and Republican women congressional candidates in 1990 and 1992. The investigation determined that media attention is related to whether the candidates are running for the Senate or House, incumbency, and state population. The results also reveal that party is a statistically significant factor associated with media attention. The investigation also determined that ethnic candidates tend to receive slightly less attention from the print media than nonethnic candidates.  相似文献   
62.
63.
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features  相似文献   
64.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications  相似文献   
65.
66.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency  相似文献   
67.
Canny  J. 《Computer Journal》1993,36(5):409-418
  相似文献   
68.
69.
Variations in lipid profile and incidence of vascular events were evaluated. Group 1 had a 29.3% reduction of total and a 38.3% reduction of LDL cholesterol as against reductions of 9% and 9.6% respectively in group 2. No significant difference was observed between the two groups as far as the vascular events considered were concerned. Pravastatin is an effective and safe drug. The lack of influence on the evolution of vascular disease would appear to be correlated to the small number of subjects studied and the short follow-up.  相似文献   
70.
Nutrient uptake by the hindlimb was investigated utilising the arteriovenous difference technique in 5 Thoroughbred horses fed to maintenance a diet of 100% roughage or 52% oat grain and 48% roughage. Arterial blood was obtained from a catheter inserted into the carotid artery while venous blood was simultaneously collected from a catheter placed into the iliac vein via the medial saphenous vein. The arteriovenous difference for glucose was significant and represented a mean extraction of 10 +/- 1% with no effect of diet. If fully oxidised, glucose uptake (corrected for lactate and pyruvate arteriovenous difference) was sufficient to account for 78 +/- 13% or 107 +/- 15% of the oxygen consumed by the hindlimb in horses fed a roughage or 52% oat grain diet respectively. Acetate was also a major metabolite of the hindlimb, showing a 39 +/- 5% extraction with no effect of diet. However, the 52% oat grain diet did induce a significant decline in the concentration of acetate in arterial blood. The potential contribution to oxidation in the hindlimb was significantly reduced from 32 +/- 4% in horses fed roughage to 21 +/- 3% when fed 52% oat grain. D-3-Hydroxybutyrate uptake could account for 9 +/- 1% of the oxidation by the hindlimb with no effect of diet. The technique for measuring nutrient uptake across the hindlimb using the arteriovenous difference is relatively simple and would be valuable in investigating fuel use by muscle during exercise.  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