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   6475篇
  免费   188篇
  国内免费   40篇
电工技术   133篇
综合类   44篇
化学工业   1281篇
金属工艺   124篇
机械仪表   189篇
建筑科学   250篇
矿业工程   45篇
能源动力   152篇
轻工业   591篇
水利工程   52篇
石油天然气   17篇
武器工业   2篇
无线电   489篇
一般工业技术   1009篇
冶金工业   1423篇
原子能技术   77篇
自动化技术   825篇
  2022年   69篇
  2021年   107篇
  2020年   52篇
  2019年   76篇
  2018年   117篇
  2017年   75篇
  2016年   110篇
  2015年   103篇
  2014年   132篇
  2013年   360篇
  2012年   235篇
  2011年   345篇
  2010年   294篇
  2009年   312篇
  2008年   358篇
  2007年   323篇
  2006年   247篇
  2005年   268篇
  2004年   172篇
  2003年   197篇
  2002年   183篇
  2001年   132篇
  2000年   137篇
  1999年   123篇
  1998年   277篇
  1997年   196篇
  1996年   159篇
  1995年   102篇
  1994年   105篇
  1993年   122篇
  1992年   66篇
  1991年   48篇
  1990年   75篇
  1989年   59篇
  1988年   53篇
  1987年   71篇
  1986年   47篇
  1985年   75篇
  1984年   72篇
  1983年   58篇
  1982年   41篇
  1981年   49篇
  1980年   49篇
  1979年   31篇
  1978年   42篇
  1977年   66篇
  1976年   77篇
  1975年   29篇
  1974年   25篇
  1973年   22篇
排序方式: 共有6703条查询结果,搜索用时 15 毫秒
1.
2.
3.
A program called GELYMAC takes data on the distances migrated by DNA fragments in a one-dimensional electrophoretic gel and, using a cubic-spline best-fit of marker fragment distance migrated versus molecular size, calculates the molecular sizes of the fragments. Written in the Rascal (Real-time Pascal) programming language, the program runs on the Macintosh family of microcomputers. Rapid entry of marker and experimental fragment migration data is afforded using a scroll bar system adjacent to a graphic representation of a gel. Output includes tabular listing of the data, graphic cartoons of the gel, and the fragment locations and molecular sizes for individual gel lanes, and the calibration curve used in data computations.  相似文献   
4.
5.
The numerical accuracy of the displacement potential approach for a three-dimensional water-impact problem is investigated. An examination of the elliptic paraboloid shows that the boundary-value problem for the displacement potential, as well as the velocity potential, can be solved accurately, even if the panel size of the numerical scheme is no small enough. The numerical accuracy of the position of the contact line is poor. However, the accuracy of the virtual mass is good because of the averaging effect along the contact line. A comparison with Scolan and Korobkin's designed body confirms the accuracy of the drop speed and the penetration displacement. The displacement potential approach is extended to the case of water impact with trapped air. The numerical accuracy of the calculated air pressure in the cavity is confirmed by comparison with an experimental result. With these results, the suitability of the displacement potential approach to the ship-slamming problem is demonstrated.  相似文献   
6.
7.
8.
9.
The breakdown processes of oil films under quasi-static loading have been investigated by using a newly developed steel-oil-mercury system. The relationship between the thickness and breakdown ratio of a hexadecane film is represented by a single master curve independently of the indentation speed, indentation load, and temperature. The master curve shows that the breakdown process of hexadecane includes two stages; one is the decrement of the thickness without breakdown and the other is the decrement of the thickness with a drastic progress of breakdown. By solving a small amount of fatty acid in hexadecane, the thickness increases and the breakdown ratio decreases noticeably; a multilayer residual film supporting normal load is formed between two metal surfaces. Experiments at different temperatures reveal a negative relationship between the temperature and thickness of residual film, which indicates that the residual film is organized by physical interaction rather than chemical interaction. At least under a lower concentration, the residual film appears to consist of not only fatty acid molecules but also hexadecane molecules.  相似文献   
10.
It is well recognized that performance changes over time. However, the effect of these changes on overall assessments of performance is largely unknown. In a laboratory experiment, we examined the influence of salient Gestalt characteristics of a dynamic performance profile on supervisory ratings. We manipulated performance trend (flat, linear-improving, linear-deteriorating, U-shaped, and ∩-shaped), performance variation (small, large), and performance mean (negative, zero, positive) within subjects and display format (graphic, tabular) between subjects. Participants received and evaluated information about the weekly performance of different employees over a simulated 26-week period. Results showed strong main effects on performance ratings of both performance mean and performance trend, as well as interactions with display format. Theoretical and practical implications of the results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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