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   9341篇
  免费   160篇
  国内免费   9篇
电工技术   105篇
综合类   2篇
化学工业   1157篇
金属工艺   113篇
机械仪表   313篇
建筑科学   229篇
矿业工程   29篇
能源动力   144篇
轻工业   965篇
水利工程   118篇
石油天然气   17篇
无线电   921篇
一般工业技术   1154篇
冶金工业   3326篇
原子能技术   117篇
自动化技术   800篇
  2021年   99篇
  2020年   73篇
  2019年   86篇
  2018年   83篇
  2017年   110篇
  2016年   90篇
  2015年   61篇
  2014年   120篇
  2013年   341篇
  2012年   190篇
  2011年   285篇
  2010年   244篇
  2009年   261篇
  2008年   286篇
  2007年   267篇
  2006年   265篇
  2005年   234篇
  2004年   189篇
  2003年   213篇
  2002年   210篇
  2001年   173篇
  2000年   168篇
  1999年   204篇
  1998年   797篇
  1997年   500篇
  1996年   431篇
  1995年   317篇
  1994年   267篇
  1993年   260篇
  1992年   119篇
  1991年   133篇
  1990年   144篇
  1989年   136篇
  1988年   135篇
  1987年   139篇
  1986年   109篇
  1985年   137篇
  1984年   101篇
  1983年   105篇
  1982年   74篇
  1981年   94篇
  1980年   79篇
  1979年   83篇
  1978年   74篇
  1977年   120篇
  1976年   205篇
  1975年   73篇
  1974年   72篇
  1973年   68篇
  1972年   57篇
排序方式: 共有9510条查询结果,搜索用时 15 毫秒
11.
To meet the criteria of role accountability, nursing competence and ongoing staff development, an improved peer-evaluation system was designed to continuously monitor these new roles. This peer-evaluation process converts evaluation input into data, giving staff a visual picture of how their performance compares within their peer group. This peer-evaluation process was designed as a tool to assist in staff growth and development, not as a punitive system.  相似文献   
12.
13.
A real-time computer system is described which minimizes the total analysis time in gel permeation chromatography by automatically acquiring the data, performing the necessary calculations and displaying the molecular weight distribution and molecular weight averages as soon as the polymer peak has eluted. The calculation method described here is valid for linear homopolymers only, and does not include corrections for instrumental peak broadening. The experimental results show good reproducibility and precision. On-line changes of the constants and other parameters may be implemented by means of an auxiliary program which runs in parallel with the data analysis program. A system such as that described here is suitable for utilization as a measurement technique in process control applications. The programs are written in CORAL 66 for a Ferranti Argus 700 E computer.  相似文献   
14.
A complete solution in closed form to the elastic contact of a one-dimensional sinusoidal surface with a flat surface was presented by Westergaard in 1939. This paper is concerned with the elastic contact of a two-dimensional sinusoidal surface with a flat. In this case the stress distribution within the elastic solids is three-dimensional. As the load is increased the contact areas change in shape from being circular to square and finally leave a circular region of no contact when the waves are almost squashed flat. The problem is solved in general using a numerical method due to Kalker, but asymptotic solutions in closed form have been found for light loads and also for heavy loads at which contact is almost complete. The variation of the mean separation with load, which determines the volume of the space trapped between the two surfaces, is also found.  相似文献   
15.
16.
John Dahlgren served in the U.S. Navy for nearly 35 years, sometimes in a sea-keeping capacity but mostly developing large naval artillery. To-day, his name, when recognised by students of naval ordnance, is associated with teh Dahlgren or ‘soda bottle shaped’ gun of 9 to 11 inch calibre. He designed, developed and lived to see his guns installed aboard warships and used to considerable effect, especially in the American Civil War. However, a nearly indistinguishable external design of gun was developed for the Army by T. J. Rodman, an officer now even less known than Dahlgren and whose researches and contributions are virtually forgotten. This paper and that in Ref. [1] attempt to appreciate (along with other technical questions of the period) the different ways pursued by these men towards the final development of the ‘soda bottle shaped’ gun, though it is a matter still not entirely understood.

Both names are totally omitted from several ‘classic’ books on artillery and this is a grave misfortune. Besides trying to throw factual light on the Dahlgren-Rodman controversy and the priority issue (though not one pursued with acrimony by the men themselves at the time), the paper describes Admiral Dahlgren's general career, the books he wrote, the technical problems he attacked and the problematic ordnance discussions of his day, to which he gave his life.

The work of Dahlgren and Rodman, in particular, saw the elevation of American gun design from the level of mere copying (of early Columbiads in the first decades of the century) to that which compelled attention from, and study by, the super-powers of the day, Great Britain, France and Russia.  相似文献   

17.
Graduates of clinical training programs were surveyed to determine the degree to which they have found various graduate school experiences useful in their professional work. Samples of academic clinical psychologists and practicing clinical psychologists reported time allocation and preference for various professional activities, perceived usefulness of various theoretical orientations, and the influence on their current professional work of 19 different graduate training topics. Results suggest that where differences exist, academic clinical psychologists are generally more satisfied with Boulder-model-inspired scientific training than are clinical practitioners. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
18.
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies.  相似文献   
19.
20.
Three applications of sampling-based sensitivity analysis in conjunction with evidence theory representations for epistemic uncertainty in model inputs are described: (i) an initial exploratory analysis to assess model behavior and provide insights for additional analysis; (ii) a stepwise analysis showing the incremental effects of uncertain variables on complementary cumulative belief functions and complementary cumulative plausibility functions; and (iii) a summary analysis showing a spectrum of variance-based sensitivity analysis results that derive from probability spaces that are consistent with the evidence space under consideration.  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