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   16692篇
  免费   1460篇
  国内免费   981篇
电工技术   3758篇
技术理论   2篇
综合类   2305篇
化学工业   2557篇
金属工艺   192篇
机械仪表   393篇
建筑科学   1650篇
矿业工程   403篇
能源动力   750篇
轻工业   910篇
水利工程   419篇
石油天然气   488篇
武器工业   64篇
无线电   868篇
一般工业技术   799篇
冶金工业   672篇
原子能技术   37篇
自动化技术   2866篇
  2024年   29篇
  2023年   170篇
  2022年   328篇
  2021年   388篇
  2020年   445篇
  2019年   382篇
  2018年   335篇
  2017年   385篇
  2016年   435篇
  2015年   435篇
  2014年   778篇
  2013年   808篇
  2012年   938篇
  2011年   1076篇
  2010年   917篇
  2009年   1013篇
  2008年   950篇
  2007年   1369篇
  2006年   1269篇
  2005年   1134篇
  2004年   1111篇
  2003年   1039篇
  2002年   815篇
  2001年   688篇
  2000年   540篇
  1999年   336篇
  1998年   263篇
  1997年   203篇
  1996年   131篇
  1995年   124篇
  1994年   103篇
  1993年   64篇
  1992年   31篇
  1991年   27篇
  1990年   14篇
  1989年   8篇
  1988年   9篇
  1987年   2篇
  1986年   7篇
  1985年   9篇
  1984年   6篇
  1983年   3篇
  1972年   1篇
  1971年   2篇
  1970年   2篇
  1964年   1篇
  1963年   2篇
  1959年   1篇
  1955年   1篇
  1954年   1篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
Designing wholesale electricity spot markets even after three decades of experience in dozens of countries continues to be a challenging task. The challenges arise from a myriad of options that exist without adequate level of unbiased guidance, and experiences in real-life markets where successes and failures are also open to the interpretation of experts. This is particularly a critical issue in the developing world where wholesale spot markets are yet to be established in 80 % of the countries and the experience in the remaining 20 % countries with an operational market, is mixed. There are certain trends in selection of market design that leave significant room for improvement including fallacies that should be avoided. Implementation of markets have also been problematic in most cases including unrealistic timetable and inadequate consideration of transition mechanism that have also hampered market development. In this article, we present our views on how policy makers, stakeholders and development institutions should think about the choices around market design and some of the common pitfalls around its implementation.  相似文献   
12.
Pu、Am、Np是3种重要的超铀核素,环境中的这些核素主要来源于人类的核活动,包括大气层核武器试验、核设施排放和核事故释放等。这些超铀核素不仅具有放射性,还兼具化学毒性。我国地域辽阔,环境土壤类型丰富,在当前核电事业蓬勃发展的背景下,建立和扩大我国环境土壤中这些重要超铀核素的“准本底”数据库是辐射环境安全评价的重要组成部分,也是公众关心的热点问题。近30多年来,研究人员对我国不同环境土壤中这几种超铀核素从不同科学角度开展了调查测量研究。本文对此进行整理和分析,对我国环境土壤中这些重要超铀核素(主要是Pu核素,还包括241Am和237Np)的来源、浓度水平和分布特征进行讨论和综述,为辐射环境安全评价奠定基础。  相似文献   
13.
Existing adaptive control algorithms at best guarantee that the tracking error is a l 2 sequence. This paper presents globally stable adaptive control algorithms for linear discrete-time systems providing l 1 tracking performance. Two algorithms with different degree of complexity are proposed, one for the case of known control directions, and a separate algorithm for the case of unknown control directions. It is demonstrated that in both cases the tracking error is l 1 sequence, while the input and output signals are uniformly bounded.  相似文献   
14.
Motivated by previous studies documenting significant return and volatility effects of economic policy uncertainty (EPU) on the stock market, this study examines whether EPU has an effect on the dynamic conditional correlations between stock and commodity returns. Our findings point to a positive and significant effect of EPU on stock-commodity correlations with particularly stronger effects in the case of energy and industrial metals. The EPU effect is stronger during weak economic conditions, while VIX as a proxy of market uncertainty is generally found to be insignificant. Finally, we show that the EPU effect on correlations has investment implications as well, implied by a significant effect on optimal hedge ratios in commodities in order to mitigate stock market risks. Our results underscore the importance of selective hedging strategies in which risk managers base the timing and size of their hedging programs on future price expectations, conditional on the level of policy uncertainty state and prevalent economic conditions.  相似文献   
15.
ABSTRACT

This paper explores intensified water crisis in Bangalore (or Bengaluru) in India by using the analytic of three hydrosocial regimes: the catchment-based regime, the hydraulic regime and the speculative urban regime. It uses a wide range of qualitative interviews, scientific reports and secondary sources to analyze shifting urban trajectories, agrarian relations and their interlinkages with water. Historical ruptures (in the realm of governance, urban growth and changing urban–rural dynamics) allow one to highlight the complex role of speculative logics that shape urban expansion and water scarcity.  相似文献   
16.
Consumption of functional foods suggests a strategy to reduce the incidence of chronic health disorders. This message has resonated with consumers and driven market growth. Functional food research has significantly increased over the last decade but few studies have addressed the bioavailability of active ingredients for clinical efficacy. Baked goods such as bread, biscuits and cake are popular categories for innovation due to their widespread consumption. These new developments have often impacted on organoleptic properties of the finished products and thus consumer acceptance. Blending of bioactive ingredients may overcome this deficit. However, an understanding of the role of the microbiome in health has indicated that the efficacy of functional foods is unlikely to be uniform within the population. Further growth in the functional foods market, is likely to require greater evidence of the bioavailability of active ingredients, clinical effect and support for health claims by regulators especially in the EU.  相似文献   
17.
针对传统规划方法难以体现水资源配置过程中多种复杂因素的问题,基于博弈理论建立宏观调控和市场经济相结合的水资源配置动态博弈模型,求解其子博弈精炼纳什均衡下各博弈参与人的策略,并运用改进量子遗传算法求解该博弈模型。对A河流域水资源配置结果表明,在保证流域公共生态用水2.0×10~8 m~3的基础上,各用水子区自发约束自身的取水量,达到均衡时,社会总收益为11.27亿元,相比自由取水模型,社会总收益增加了0.95亿元,增幅为9.2%。  相似文献   
18.
With the growing role of distributed energy resources, the electricity network is challenged by numerous technical problems, such as capacity congestion and over- or under-voltage. An often-discussed response, especially in the European zonal electricity system, is to implement regional flexibility markets. We contribute to this discussion by providing a comprehensive classification framework for the design of flexibility products by combining technical requirements with classical auction theory. The framework structures 23 product parameters in four stages of abstraction. By applying the framework to five market approaches used in current German research projects, we demonstrate its usefulness for consistent comparison of flexibility products at a high level of detail. This framework can empower national and international policymakers and practitioners in assessing flexibility markets holistically, thereby facilitating the implementation of sound solutions.  相似文献   
19.
Blockchain possesses the potential of transforming global supply chain management. Gartner predicts that blockchain could be able to track $2?T of goods and services in their movement across the globe by 2023, and blockchain will be a more than $3 trillion business by 2030. Nowadays, a growing number of blockchain initiatives are disrupting traditional business models in each sector. In this paper, we provide a timely and holistic overview of the state-of-the-art, challenges, gaps and opportunities in global supply chain and trade operations for both the private sector and governmental agencies, by synthesising a wide range of resources from business leaders, global international organisations, leading supply chain consulting firms, research articles, trade magazines and conferences. We then identify collaborative schema and future research directions for industry, government, and academia to jointly work together in ensuring that the full potential of blockchain is unleashed amidst the socioeconomic, geopolitical and technological disruptions that global supply chains and trade are facing.  相似文献   
20.
Location plays a major role in the building of artistic, technological or scientific movements that emerge in specific locations before achieving a worldwide reach. However, a deeper understanding is needed about the interplay of local/global knowledge dynamics in the epistemic construction of a movement. Based on an in-depth longitudinal study of a critical case, this article sheds light on these issues by analysing the case of ‘techno-emotional cuisine’, a global gastronomic movement initiated and led by chef Ferran Adrià and his team at the restaurant elBulli in Catalonia (in Northern Spain). The results suggest that the dynamics of formation of a new epistemic movement depend on the form and nature of the interactions between the local buzz and global pipelines, and on the capacity of the originating community to develop and diffuse the new rules and ‘episteme’ on a global scale while consolidating them locally.  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