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   6368篇
  免费   885篇
  国内免费   447篇
电工技术   322篇
技术理论   2篇
综合类   647篇
化学工业   143篇
金属工艺   11篇
机械仪表   35篇
建筑科学   947篇
矿业工程   151篇
能源动力   326篇
轻工业   58篇
水利工程   4374篇
石油天然气   305篇
武器工业   6篇
无线电   43篇
一般工业技术   78篇
冶金工业   44篇
原子能技术   11篇
自动化技术   197篇
  2024年   11篇
  2023年   93篇
  2022年   155篇
  2021年   201篇
  2020年   207篇
  2019年   227篇
  2018年   192篇
  2017年   250篇
  2016年   290篇
  2015年   305篇
  2014年   398篇
  2013年   367篇
  2012年   471篇
  2011年   484篇
  2010年   362篇
  2009年   352篇
  2008年   339篇
  2007年   437篇
  2006年   423篇
  2005年   372篇
  2004年   281篇
  2003年   232篇
  2002年   241篇
  2001年   195篇
  2000年   130篇
  1999年   134篇
  1998年   89篇
  1997年   77篇
  1996年   78篇
  1995年   53篇
  1994年   46篇
  1993年   38篇
  1992年   49篇
  1991年   24篇
  1990年   17篇
  1989年   27篇
  1988年   18篇
  1987年   11篇
  1986年   4篇
  1985年   11篇
  1984年   4篇
  1983年   2篇
  1982年   1篇
  1980年   1篇
  1979年   1篇
排序方式: 共有7700条查询结果,搜索用时 78 毫秒
1.
寒区河道凌汛灾害河势“弯道效应”的量化评估十分重要。基于分形理论提出河道横断面-纵剖面-平面多维度河势分形维数计算方法及其物理机制,并探讨黄河内蒙古段不同维度河势演变分形特征及其与凌汛灾害的关联关系。结果表明,黄河内蒙古段不同维度河势均具有多尺度自相似分形特征,且具有多年记忆周期的长程相关性;冰坝(严重性冰塞)发生频次与河道主槽弯曲分形维数呈正相关指数型函数关系,与河相系数、深泓点高程和河段平均底坡分形维数负相关,与水深-面积分形维数正相关,总体表明冰坝灾害更易发生于主槽偏移摆动大、蜿蜒曲折、河湾发育程度高的宽浅型弯曲河道,研究成果可为凌汛期冰塞冰坝灾害易发河段诊断及预测提供重要理论依据。  相似文献   
2.
3.
4.
下击暴流等极端风具有强烈的非平稳特性,给风场特性分析、结构响应计算带来挑战。根据经验将非平稳风分为时变平均风和零均值脉动风分别进行分析,是处理非平稳风速信号的有效方法。分析了几种常见时变均值提取方法的优缺点,在此基础上提出一种基于能量波谷寻找的经验小波变换方法,用于下击暴流时变平均风速提取,并将提取的时变平均风和脉动风用于分析某幢高层建筑顶部位移响应。对2组下击暴流的分析结果得出:与经验模态分解和离散小波变换方法相比,基于能量波谷寻找的经验小波变换方法模型提取的时变平均风更符合预期,对应的结构响应偏于安全。  相似文献   
5.
推进澜湄合作是构建周边命运共同体的具体实践,以“同饮一江水,命运紧相连”为主题的澜湄合作机制也为构建澜湄国家命运共同体提供了推进方向。环境问题是澜湄流域最为核心的问题之一,面向澜湄合作中的环境利益问题,文章结合共同体的理念,基于霍尔三维结构理论,总结出合作伙伴环境利益共同体模式、合作联盟环境利益共同体模式与一体化环境利益共同体模式的三种环境利益共同体模式,通过建立环境利益共同体模式的评价指标体系,利用网络层次分析法对澜湄环境利益共同体模式进行评价,选择适合澜沧江-湄公河的环境利益共同体模式。结果表明,在当前的澜湄现状下,以“澜湄六国通过开发流域资源发展本国经济而同时受到其他主体监督以保证不破坏澜沧江-湄公河的生态环境”为主要内容的合作联盟环境利益共同体模式更适合澜湄流域各国,这一模式可以有效解决流域各国经济与环境“两难重”的困境。  相似文献   
6.
7.
ABSTRACT

Recent grants of legal rights to rivers would seem to infuse traditional anthropocentric river governance with greater eco-centrism. Through a thought experiment, we scrutinize this proposition for the Rhine basin. We consider the governance implications of granting (procedural/material) rights to the river and elaborate on their implications for the three highly institutionalized regimes of the Rhine River of water quality, flooding and transport. Since we find that a shift to more eco-centrism has already occurred and since the right granted to the river would not be absolute, we deem radical transformations unlikely.  相似文献   
8.
Because lately the low bioindicative value of tolerant species from different taxonomic groups is often questioned, in this study, we hypothesized that tolerant diatoms may be used for effective temporal assessments of human pressure. We tested this on the lowland Bzura River in central Poland, on 156 diatom samples (DSs) from two study periods of 1972 with extremely severe point‐source water pollution and of 2002–2004, where the complex wastewater management in the river catchment improved water quality considerably. Out of the total 295 diatom species recorded in the samples, only 133 tolerant ones were included in the study. Patterns in their abundance were recognized with a Kohonen artificial neural network (self‐organizing map, SOM), whereas the species significantly associated with each SOM cluster of diatom samples were identified with the indicator value (IndVal) index and the Monte Carlo test. If the hypothesis tested was not supported, the assignation of DSs to the SOM clusters would be random. However, the separation of DSs from 1972 and 2002–2004 was almost perfect because the number of exceptions was as low as 4.5%. In addition, the relatively high number (64 out of 133) of tolerant species significantly associated with any SOM cluster (and respective environmental conditions at sites from which samples assigned to it come) supports the hypothesis tested. This means that almost half of the studied species are not evenly distributed in particular clusters as might be expected for highly tolerant species. The study proves that the abundances of many diatom species, currently classified as tolerant, carry quite precise information on the differences in the quality of the environment, and indicates those tolerant diatom species whose bioindicative potential may be highest. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
9.
The ‘project risk screening matrix’ derives from a broader effort to assist US government agency staff in reviewing proposed stream management and restoration projects more efficiently and effectively. The River Restoration Analysis Tool (RiverRAT) developed through this effort provides a thorough, comprehensive and auditable approach to review and evaluate proposed stream actions and projects ( www.restorationreview.com ). The matrix was initially developed as the first step in applying the RiverRAT, its purpose being to assist reviewers in assessing the risk to natural resources associated with a particular proposal and matching the intensity of their review to the severity of that risk. Hence, the primary application of the matrix to date has been to identify and screen out low risk projects that may be dealt with expeditiously, so freeing the time and technical resources needed to allow deep reviews of higher risk projects. A second form of screening emerged from this primary function because the matrix proved adept at identifying the minimum level of site and project characterization required to support initial risk assessment. On this basis, proposals lacking adequate information can also be screened out, being referred back to the proponent with a request for additional information. More recently, new and novel versions of the matrix, featuring modification and refinement of one or both of the original axes, have emerged to widen and refine its application to linear infrastructure (e.g. pipelines, roads, and electrical transmission lines), in‐stream structures (e.g. large wood placement and culvert removal), and pre‐application, regulatory, decision‐support tools. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   
10.
As suggested by the uncanny valley hypothesis, robots that resemble humans likely elicit feelings of eeriness. Based on the psychological model of meaning maintenance, we expected that the uncanny valley experience could be mitigated through a fictional story, due to the meaning-generating function of narratives. A field experiment was conducted, in which 75 participants interacted with the humanlike robot Telenoid. Prior to the interaction, they either read a short story, a non-narrative leaflet about the robot, or they received no preliminary information. Eeriness ratings were significantly lower in the science fiction condition than in both other conditions. This effect was mediated by higher perceived human-likeness of the robot. Our findings suggest that science fiction may provide meaning for otherwise unsettling future technologies.  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