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   32055篇
  免费   1411篇
  国内免费   34篇
电工技术   340篇
综合类   57篇
化学工业   6966篇
金属工艺   597篇
机械仪表   577篇
建筑科学   1885篇
矿业工程   77篇
能源动力   873篇
轻工业   2686篇
水利工程   295篇
石油天然气   165篇
武器工业   3篇
无线电   2288篇
一般工业技术   5924篇
冶金工业   5203篇
原子能技术   206篇
自动化技术   5358篇
  2023年   277篇
  2022年   447篇
  2021年   696篇
  2020年   507篇
  2019年   591篇
  2018年   721篇
  2017年   691篇
  2016年   908篇
  2015年   813篇
  2014年   1027篇
  2013年   1919篇
  2012年   1669篇
  2011年   2121篇
  2010年   1510篇
  2009年   1464篇
  2008年   1761篇
  2007年   1645篇
  2006年   1442篇
  2005年   1228篇
  2004年   1093篇
  2003年   945篇
  2002年   912篇
  2001年   542篇
  2000年   523篇
  1999年   532篇
  1998年   490篇
  1997年   446篇
  1996年   458篇
  1995年   438篇
  1994年   425篇
  1993年   429篇
  1992年   384篇
  1991年   229篇
  1990年   319篇
  1989年   321篇
  1988年   271篇
  1987年   296篇
  1986年   286篇
  1985年   306篇
  1984年   267篇
  1983年   257篇
  1982年   239篇
  1981年   209篇
  1980年   175篇
  1979年   182篇
  1978年   165篇
  1977年   135篇
  1976年   122篇
  1975年   134篇
  1974年   109篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
41.
42.
Hong Kong is known as a migrant city because its population was sourced from mainland China, and because there has always been outflows of people to overseas countries, especially from the mid-1980s to mid-1990s. Emigration to mainland China has become a significant recent trend. This article discusses this phenomenon in the theoretical contexts of migration and trans-border residential development. It contends that the trend will intensify more quickly than other cross-border movements because the two systems are separated by a political border within one country, and because there are common cultural ties and rapid economic integration.  相似文献   
43.
44.
A new approach to the combination of exergetic and economic analysis (exergoeconomic analysis) for the investigation of energy-conversion processes is presented. This approach allows the monetary evaluation of costs caused by irreversibilities (exergy losses), as well as comparisons between these costs and the investment and operating costs for each component of a plant. The present analysis permits identification and evaluation of inefficiencies in an energy-conversion plant and of opportunities for improvement.  相似文献   
45.
Abstract: This article combines the neighborhood effects and spatial mismatch frameworks into a single model explaining how geographic factors contribute to unemployment. Using National Longitudinal Survey of Youth (1979) data, I estimate a two‐step model that separately models the effects of segregation and spatial mismatch. The first model predicts educational attainment as a function of exposure to residential segregation as a youth. The second model predicts unemployment probability as an adult as a function of educational attainment and spatial mismatch. The empirical results show that segregation does have discernable effects on educational attainment for blacks, but not for whites. I also find that spatial mismatch affects unemployment probability for blacks, but such an effect is hardly present for whites. A partial equilibrium analysis using predictions from the models shows that large changes in either segregation levels or the central city/suburban distribution of the black population would yield only moderate decreases in unemployment probability for the black population overall. Yet despite small predicted effects, these results should be viewed with caution because the general equilibrium effects of a large scale movement of blacks and whites across metropolitan space are largely impossible to predict with current data.  相似文献   
46.
47.
All fields of engineering, whether chemical, civil, electrical, materials, mechanical, etc., encompass a common body of essential mathematics and science. In the freshman year of Drexels E4 program, this common mathematical and scientific foundation is cultivated in the Mathematical and Scientific Foundations of Engineering I, II and III (MSFE I, MSFE II, MSFE III). In an integrated fashion, MSFE I presents the essential calculus, physics and engineering mechanics vital to the freshman engineering student. In the first two quarters, MSFE II presents chemistry with clearly defined engineering applications and significance: in the third quarter, MSFE II presents living systems with the same thrust. Also in the third quarter, MSFE III presents basic circuits and circuit elements, and a brief introduction to electromagnetic theory.  相似文献   
48.
Water Resources Management - Sustained pumping of groundwater can lead to declining water levels in wellfields and concerns regarding the sustainability of groundwater resources. Aquifer Storage...  相似文献   
49.
The hydrodynamics of superfluids in confined geometries (capillaries, porous media, etc.) is investigated theoretically. Hydrodynamic equations are derived. The mode structure is calculated, i.e., explicit expressions for the dispersion relationsq=q() are given. Experimental applications for4He-II and superfluid3He are discussed.  相似文献   
50.
Distributed and Parallel Databases - Given two datasets of points (called Query and Training), the Group (K) Nearest-Neighbor (GKNN) query retrieves (K) points of the Training with the smallest sum...  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