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   4415篇
  免费   287篇
  国内免费   15篇
财政金融   33篇
工业经济   242篇
计划管理   1384篇
经济学   618篇
综合类   300篇
运输经济   5篇
旅游经济   39篇
贸易经济   207篇
农业经济   1539篇
经济概况   350篇
  2024年   18篇
  2023年   66篇
  2022年   133篇
  2021年   98篇
  2020年   113篇
  2019年   113篇
  2018年   128篇
  2017年   112篇
  2016年   160篇
  2015年   210篇
  2014年   301篇
  2013年   241篇
  2012年   375篇
  2011年   452篇
  2010年   418篇
  2009年   236篇
  2008年   233篇
  2007年   248篇
  2006年   291篇
  2005年   225篇
  2004年   122篇
  2003年   95篇
  2002年   86篇
  2001年   83篇
  2000年   60篇
  1999年   26篇
  1998年   9篇
  1997年   15篇
  1996年   14篇
  1995年   9篇
  1994年   4篇
  1993年   10篇
  1992年   7篇
  1985年   2篇
  1984年   2篇
  1980年   1篇
  1979年   1篇
排序方式: 共有4717条查询结果,搜索用时 15 毫秒
71.
Water fluoridation is a controversial issue in public health. Despite the uncertainty regarding its efficacy and safety, health officials continue to communicate it as ‘unequivocally’ safe and effective. Our focus is on how health officials and policy-makers in Israel frame the issue of water fluoridation in terms of certainty while promoting a mandatory fluoridation policy. According to van Asselt and Vos, the uncertainty paradox describes situations in which uncertainty is acknowledged, but the role of science is framed as providing certainty. Our study is an analysis of documents and media articles emphasizing the paradoxical language used by official representatives on the controversial topic of fluoridation. A central contribution of this study is that we coin the term ‘uncertainty bias,’ in which policy-makers do exactly what they accuse laypeople of doing, framing uncertainty in biased terms. We found that in order to establish mandatory regulation, health ministry officials expressed information in an unbalanced format, promoting the topic of fluoridation by framing it in exclusively positive terms. This study does not focus on the practice of water fluoridation per se, and is not intended to decide for or against it, but rather, to explore how the debate regarding it is communicated. Understanding this particular case can shed light on how other controversial topics are transformed into health policy that is characterized in equivocal terms.  相似文献   
72.
73.
离子色谱是高效液相色谱法当中的一类,又被称之为现代离子色谱。作为一种高效科学的检测方法,离子色谱发展迅速,被广泛用于大气、土壤和水质检测中。本文主要综述了离子色谱法应用于生活饮用水检测的研究进展。  相似文献   
74.
Land exploitation, as an important strategy to mitigate farmland loss and stabilize grain production, has been adopted to compensate farmland loss due to rapid urbanization in China. Bounded by the limited capacity and obvious spatial variations of national farmland reserves, it is essential to arrange land exploitation activities timely and reasonably. In this study, we propose an indicator for the status of regional land exploitation, the Exploitation Degree, to facilitate an overview of land exploitation programs in China at both provincial and prefectural levels based on project data from 2006 to 2012. To further our understanding of the regional features of land exploitation activities, we employ the Lasso model to identify and quantitatively assess influencing factors on land exploitation. Our study shows that: (1) contemporary land exploitation practices in China are significantly inconsistent across exploitable farmland reserves. Some areas are greatly over-exploited and such irrational land exploitation has been persistent; (2) related national land plans designed to guide land exploitation efforts centered on resource-rich regions and critical areas do not function as intended. Therefore, we suggest that China⿿s land exploitation policy shall be improved by reconsidering the orientation of land exploitation policy, coordinating land exploitation activities with productivity improvements and eco-system protection, and enhancing the power and scope of the plans in controlling and guiding land resource management.  相似文献   
75.
At the beginning of the 21st century, the Netherlands and Flanders introduced a risk-based approach to flood risk management (FRM), labelled as multi-layer (water) safety. In contrast to a flood defence approach, risk-based management stresses the need to manage both the consequences and probability of a flood. The concept has developed differently in the two countries, as we conclude from a discursive-institutionalist research perspective. The Netherlands is characterised by a high institutionalization of the traditional flood defence discourse and a more closed policy arrangement, whereas in Flanders, the flood defence discourse is less institutionalized and the arrangement is more open. In both countries we see an opening of the arrangement preceding the establishment of multi-layer (water) safety, but at the same time, actors stress different aspects of the concept in order to increase its compatibility with the existing policy arrangement. In the Netherlands, the focus is on probability management, in Flanders on consequence management. In the Netherlands, multi-layer (water) safety as a concept could be established because it stabilises the system in the short-term by reinforcing the importance of flood defence, whereas in Flanders, policymakers were receptive to the concept because it supports a shift of responsibility towards actors outside traditional water management.  相似文献   
76.
Air and groundwater temperatures were measured in a rimstone pool in Postojna Cave, to advise evaluation of the impact of natural and anthropogenic influences related to heat being initially transmitted into cave air by visitors. Such heat can accumulate both in the rock mass and in water. Results show that attention must be paid to temperature changes of rimstone pool water rather than those of cave air, especially during the winter. Thanks to good ventilation deep inside the cave, short-term air temperature increases related to higher visitor numbers have not influenced flowstone precipitation or the cave fauna. However, this situation might change if winter visitor numbers increased greatly. This study does not support a suggested increase in winter visits (currently the tourism low-season) and reduction of summer visits (currently the tourism high-season).  相似文献   
77.
巷道快速掘进技术是一项系统工程。为了实现矿井高产高效,必须以巷道快速掘进技术为前提和保障。本文以贵州省为例,探讨了巷道快速掘进技术的研究现状及影响因素。针对贵州某矿突出综合检测指标经常超限、掘进速度慢等问题,采用了高压水射流割缝与瓦斯抽放边抽边掘相结合技术。研究表明:该项技术能有效削弱煤层突出危险性,大幅度提高瓦斯抽放量且巷道掘进速度提高了2~3倍。同时根据贵州省的本土情况,提出了针对性地建议和措施,能为巷道快速掘进技术的推广与应用提供一定的指导。  相似文献   
78.
矿井工作面瓦斯超限严重影响着矿井安全生产和生产效率,现用解决该问题的方法存在局限性,不能广泛适用于所有矿井。针对该问题,采用水及含添加剂水阻碍和延缓煤体内瓦斯解吸速度,以达到降低工作面瓦斯涌出量的目的。本文通过对其抑制原理相关研究的介绍,为同类工作面瓦斯超限治理提供基础理论依据。  相似文献   
79.
王平  王肖霞 《价值工程》2014,(29):70-71
文章分析了锅炉水位控制系统的基本原理及结构,针对传统PID控制器的不足之处设计了基于遗传算法的新型锅炉水位控制器,在此基础上搭建了锅炉水位控制系统。最后,通过仿真验证了该水位控制器在改善水位系统稳态误差及动态超调方面均具有较好的作用。  相似文献   
80.
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