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   7170篇
  免费   464篇
  国内免费   488篇
电工技术   308篇
技术理论   8篇
综合类   770篇
化学工业   236篇
金属工艺   46篇
机械仪表   133篇
建筑科学   1335篇
矿业工程   214篇
能源动力   911篇
轻工业   229篇
水利工程   284篇
石油天然气   224篇
武器工业   16篇
无线电   543篇
一般工业技术   420篇
冶金工业   551篇
原子能技术   14篇
自动化技术   1880篇
  2024年   24篇
  2023年   74篇
  2022年   144篇
  2021年   137篇
  2020年   177篇
  2019年   152篇
  2018年   166篇
  2017年   181篇
  2016年   242篇
  2015年   252篇
  2014年   404篇
  2013年   606篇
  2012年   407篇
  2011年   554篇
  2010年   478篇
  2009年   484篇
  2008年   478篇
  2007年   546篇
  2006年   495篇
  2005年   412篇
  2004年   312篇
  2003年   287篇
  2002年   202篇
  2001年   174篇
  2000年   119篇
  1999年   108篇
  1998年   71篇
  1997年   59篇
  1996年   57篇
  1995年   39篇
  1994年   33篇
  1993年   22篇
  1992年   19篇
  1991年   16篇
  1990年   16篇
  1989年   15篇
  1988年   14篇
  1987年   8篇
  1986年   7篇
  1985年   23篇
  1984年   16篇
  1983年   9篇
  1982年   8篇
  1981年   9篇
  1979年   6篇
  1975年   6篇
  1972年   4篇
  1966年   6篇
  1956年   4篇
  1954年   3篇
排序方式: 共有8122条查询结果,搜索用时 125 毫秒
31.
On irrigation schemes with rotational irrigation systems in semiarid tropics, the existing rules for water allocation are based on applying a fixed depth of water with every irrigation irrespective of the crops, their growth stages, and soils on which these crops are grown. However, when water resources are scarce, it is necessary to allocate water optimally to different crops grown in the irrigation scheme taking account of different soils in the command area. Allocating water optimally may lead to applying less water to crops than is needed to obtain the maximum yield. In this paper, a three stage approach is proposed for allocating water from a reservoir optimally based on a deficit irrigation approach, using a simulation-optimization model. The allocation results with a deficit irrigation approach are compared for a single crop (wheat) in an irrigation scheme in India, first with full irrigation (irrigation to fill the root zone to field capacity) and second with the existing rule. The full irrigation with a small irrigation interval was equivalent to adequate irrigation (no stress to the crop). It is found that practicing deficit irrigation enables the irrigated area and the total crop production in the irrigation scheme used for the case study to be increased by about 30–45% and 20–40%, respectively, over the existing rule and by 50 and 45%, respectively, over the adequate irrigation. Allocation of resources also varied with soil types.  相似文献   
32.
Forensic psychology has made important gains in professional recognition and stature in the courts, resulting in increasing demands for mobility of expertise. Current regulations regarding the interjurisdictional temporary forensic practice of psychology, however, are characterized by variability of regulations, ambiguity and inaccessibility, and continuing total barriers. A uniform, well-reasoned policy is needed. A conceptual basis for such a policy is provided by a discussion of licensing rationales and the application of these to forensic practice. Uniformity, public and professional protection, and practicability are identified as fundamental regulatory criteria. A Model Rule Regarding the Temporary Forensic Practice of Psychology is proposed for adoption by state licensing boards on a nationwide basis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
33.
富县探区三叠系延长组长6段普遍见到不同级别的油气显示,但试油未能获得工业油流.据分析,该区白垩纪末的抬升和翘倾运动使油气发生了第三次运移成藏,油、气、水重新分布并受储层物性控制.正确勾画出有利沉积相带、针对油藏特征采取更有效的工艺技术,是实现该区勘探突破的关键.  相似文献   
34.
35.
油田开发经济运行质量研究与应用   总被引:1,自引:1,他引:0  
提出了油田开发经济运行质量的研究方法和技术思路。对胜利油区几种典型的油藏类型进行了经济运行质量评价。以老河口油田桩106块为例,提出了提高油田经济运行质量的三条基本途径,取得了较好的实际应用效果。  相似文献   
36.
李学农 《世界电信》1998,11(6):45-48,25
受中国电信委托、原邮电部经济技术发展研究中心在全国进行一次农村电信市场调查,以了解当前农村通信市场发展潜力,本文公布了此次调查的结果,从经济能力、资费和潜在市场等方面提出了发展农话的建议 。  相似文献   
37.
The use of computer models offers a general and flexible framework that can help to deal with some of the complexities and difficulties associated with the development of water management plans as prescribed by the Water Framework Directive. However, despite the advantages modelling presents, the integration of information derived from models into policy is far away from being trivial or the norm. Part of the difficulties of this integration is rooted in the lack of confidence policy makers have on the incorporation of modelling information into policy formulation. In this paper we examine the reasons for this apparent lack of confidence and explore how some tools, presently in use, address this problem. We conclude that public confidence in models is highly dependent on the way uncertainties are addressed and suggest possible directions of action to improve the current situation. Four real case studies illustrate how computer models have been used in The Netherlands for carrying out management plans at regional and national scale. We suggest that the solution to integrate modelling information into policy formulation lies on both the modelling and the policy-making communities.  相似文献   
38.
宋博通 《城市规划学刊》2002,(4):65-68,73
本文对美国低收入阶层住房政策的演化过程作了介绍 ,分析了其中三种典型住房政策的实施效果。在把握我国国情的基础上 ,借鉴美国住房政策演化过程的经验教训 ,为建立我国弱势人群住房政策提出了建议。  相似文献   
39.
For a case-study of a wafer scanner from the semiconductor industry it is shown how model checking techniques can be used to compute (1) a simple yet optimal deadlock avoidance policy, and (2) an infinite schedule that optimizes throughput. in the absence of errors. Deadlock avoidance is studied based on a simple finite state model using Smv, and for throughput analysis a more detailed timed automaton model has been constructed and analyzed using the Uppaal tool. The Smv and Uppaal models are formally related through the notion of a stuttering bisimulation. The results were obtained within 2 weeks, which confirms once more that model checking techniques may help to improve the design process of realistic, industrial systems. Methodologically, the case study is interesting since two models were used to obtain results that could not have been obtained using only a single model. Supported by the European Community Project IST-2001-35304 (Ametist), http://ametist.cs.utwente.nl/.  相似文献   
40.
Economic ideas and processes are becoming increasingly integrated with more traditional engineering and hydrologic models of water management problems. Combining economic management concepts and performance indicators with an engineering-level of understanding of a hydrologic system can provide results and insights more directly relevant for water management decisions and policies. When such models are developed and used with involvement of stakeholders, they can become a basis for shared understanding of water problems as a foundation for negotiated management and policy solutions. When implemented with optimization software, integrated hydro-economic models also can suggest promising innovative solutions for policy-makers to consider. Their applications to river basin management problems are reviewed. Economic and integrated economic-engineering-hydrologic modeling is then discussed in the context of the evolving European Water Framework Directive. Relevant items are cost recovery and water pricing, cost-effectiveness of water management measures, and public participation in decision processes.  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