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   12041篇
  免费   638篇
  国内免费   304篇
电工技术   3376篇
技术理论   2篇
综合类   1392篇
化学工业   2342篇
金属工艺   166篇
机械仪表   134篇
建筑科学   1269篇
矿业工程   323篇
能源动力   608篇
轻工业   757篇
水利工程   295篇
石油天然气   397篇
武器工业   7篇
无线电   381篇
一般工业技术   356篇
冶金工业   555篇
原子能技术   7篇
自动化技术   616篇
  2024年   17篇
  2023年   99篇
  2022年   162篇
  2021年   244篇
  2020年   270篇
  2019年   199篇
  2018年   155篇
  2017年   162篇
  2016年   224篇
  2015年   203篇
  2014年   492篇
  2013年   382篇
  2012年   525篇
  2011年   638篇
  2010年   603篇
  2009年   722篇
  2008年   656篇
  2007年   1028篇
  2006年   970篇
  2005年   887篇
  2004年   884篇
  2003年   880篇
  2002年   663篇
  2001年   550篇
  2000年   438篇
  1999年   266篇
  1998年   190篇
  1997年   140篇
  1996年   86篇
  1995年   85篇
  1994年   71篇
  1993年   37篇
  1992年   14篇
  1991年   10篇
  1990年   6篇
  1989年   1篇
  1988年   3篇
  1986年   1篇
  1985年   6篇
  1984年   2篇
  1983年   1篇
  1982年   1篇
  1979年   1篇
  1974年   1篇
  1972年   1篇
  1971年   2篇
  1970年   2篇
  1964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 62 毫秒
1.
童长征 《橡胶科技》2020,18(2):0069-0076
2019年天然橡胶期货市场起起落落,沪胶价格继续低位震荡。2020年天然橡胶供大于求的局面仍不会发生根本性改变,由极端天气引发的天然橡胶市场行情变动可能会减小,汽车行业可能会在政策支持下再次振兴,尤其重型卡车市场会成为亮点,轮胎企业继续寻求扩大出口。2020年上半年,天然橡胶期货市场可能还会受到2019年异常天气和病害等的余波作用,胶价会达到一个相对的高点,价格底部抬升,但很难出现持续性上涨的市场行情。2020年下半年,随着天然橡胶产量的季节性增长,胶价可能会再次回落。  相似文献   
2.
This article presents a metaheuristic approach, the binary whale optimization algorithm (BWOA), to solve complex, constrained, non-convex, binary-nature profit-based unit commitment (PBUC) optimization problems of a price-taking generation company (GenCo) in the electricity market. To simulate the binary-nature PBUC problem, the continuous, real-value whale position/location is mapped into binary search space through various transfer functions. This article introduces three variants of BWOA using tangential hyperbolic, inverse tangent (arctan) and sigmoidal transfer functions. The effectiveness of the BWOA approaches is examined in test systems with different market mechanisms, i.e. an energy-only market, and energy and reserve market participation with different reserve payment methods. The simulation results are presented, discussed and compared with other existing approaches. The convergence characteristics, solution quality and consistency of the results across different BWOA variants are discussed. The superiority and statistical significance of the proposed approaches with respect to existing approaches is also presented.  相似文献   
3.
We propose a general framework to study the relationship between the price of a painting and its color‐related attributes. To this end we focus on four key aspects: dominant colors, features of the color palette, color harmony, and color emotions. We demonstrate the usefulness of this approach with an example based on Mark Rothko's post‐1950 paintings (the “rectangular” series), and auction data from the 1994 to 2018 period. We identify two distinct price‐color regimes in Rothko's market: (a) [1994‐2005], a period in which prices are explained mainly by the growing popularity of the artist regardless of the color attributes of the paintings sold; and (b) [2006‐2018], a period in which color‐related attributes explain most of the prices. Furthermore, we find that in this second period, the dominant colors and the diversity of the color palette, are by far the most relevant attributes that influence the price; color harmony and color emotions hold almost no explanatory power during this period. Finally, we propose a new metric based on the Herfindahl Index to describe color diversity; this metric seems to be promising at characterizing the effect of the color palette on the price of a painting.  相似文献   
4.
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   
5.
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   
6.
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   
7.
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   
8.
The analysis of a supervision environment is the first step for a company to enter the new electricity market. Transmission and distribution assets are the main investment targets of a company. The overseas power market belongs to the regulated industry; whether it is a stock M&A project or a green land bidding project, the regulatory environment determines the assets. The level of return and investment risk that guides the operation strategy of existing overseas assets, has a significant impact on the investment and operations of international companies. A comprehensive and rapid assessment of the regulatory environment can help the project teams of international companies understand the macroenvironment of the target electricity market within a short period, quickly identify investment risks, qualitatively analyze the return level of the underlying assets, shorten the decision time, capture investment opportunities, and enhance the team. Efficiency and quality of work are factors of great importance.  相似文献   
9.
为研究多时间尺度电力交易下配电网的最大供电能力,首先从中长期+现货交易模式入手,将多时间尺度下的交易转变为单时间尺度交易;其次,建立考虑多时间尺度电力交易市场下的配电网最大供电能力双层模型,并运用原始对偶内点法和改进的重复潮流算法求解;最后通过算例,对中长期+现货交易模式下的配电网最大供电能力进行计算分析。结果表明,考虑多尺度电力交易下的配电网最大供电能力得到了提升,且随着现货交易的深入,提升得越明显。研究成果可为电力市场环境下提升配电网最大供电能力提供参考。  相似文献   
10.
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   
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