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   552篇
  免费   13篇
  2024年   1篇
  2023年   5篇
  2022年   10篇
  2021年   5篇
  2020年   10篇
  2019年   15篇
  2018年   15篇
  2017年   16篇
  2016年   18篇
  2015年   13篇
  2014年   18篇
  2013年   40篇
  2012年   43篇
  2011年   31篇
  2010年   33篇
  2009年   27篇
  2008年   33篇
  2007年   31篇
  2006年   20篇
  2005年   35篇
  2004年   25篇
  2003年   18篇
  2002年   21篇
  2001年   22篇
  2000年   18篇
  1999年   8篇
  1998年   8篇
  1997年   5篇
  1996年   3篇
  1995年   6篇
  1994年   3篇
  1993年   2篇
  1992年   4篇
  1991年   1篇
  1990年   1篇
  1982年   1篇
排序方式: 共有565条查询结果,搜索用时 15 毫秒
11.
Is urbanization good for the environment? This paper establishes a simple core–periphery model with monocentric cities, which comprises key forces that shape the structure and interrelation of cities to study the impact of the urban evolution on the environment. We focus on global warming and the potential of unfettered market forces to economize on emissions. The model parameters are chosen to match the dichotomy between average “large” and “small” cities in the urban geography of the United States, and the sectoral greenhouse gas emissions recorded for the United States. Based on numerical analyzes we find that a forced switch to a system with equally sized cities reduces total emissions. Second, any city driver which pronounces the asymmetry between the core and the periphery drives up emissions in the total city system, too, and the endogenous adjustment of the urban system accounts for the bulk of the change in emissions. Third, none of the city drivers gives rise to an urban environmental Kuznets curve according to our numerical simulations. Finally, the welfare‐maximizing allocation tends to involve dispersion of cities and the more so the higher is the marginal damage from pollution.  相似文献   
12.
文化消费的比重较大是小康型消费结构的一个重要标志,20世纪90年代北京城市居民的生活水平率先实现了小康,在居民文化消费支出不断增加的基础上,文化消费的内容日渐丰富,其中最为突出的是教育消费比重增长迅速、书报杂志消费异军突起、文娱消费浪潮不断高涨、旅游消费持续升温、休闲消费成为时尚。随着人们的视野开阔和思想解放,文化消费的领域仍在扩展之中。与乡村居民和其他城市居民相比较,北京城市居民的文化消费水平处于一个较高的位置。  相似文献   
13.
清末民初的农会组织大体经历了酝酿、兴起、发展、隐退四个阶段.其基本结构表现为组成了一个层层连接的直属组织系统;建立了较为完备的领导体制;实行了严格的民主选举制度、议事办事原则以及定期的会议制度等.呈现出组织制度的近代民主性、一定程度的自治性、成员构成的复杂性、机构权限的官督性等基本特点.所从事的活动内容相当广泛,主要表现为编辑农报,翻译农书;创办农业学堂;开办农业试验场;举行农产品评会,设立陈列所;开展调查研究;向主管官署建议农业改良进行事宜,等等.这对推动近代中国农业发展具有重要的影响与作用.  相似文献   
14.
袁书琪  刘丽 《旅游科学》2007,21(4):8-11
海峡西岸旅游产业在全国和亚太地区占有重要地位,旅游产业结构布局的调整有重大意义.当前海峡西岸旅游产业偏重观光游览,旅游投入偏少;偏重自然景观,旅游文化发掘不够;偏重旅行消费,旅游六要素不完备;偏重旅游旺季,时间上经营不平衡;偏重低级竞争,市场无序现象还比较严重.旅游产业布局存在旅游集散地与目的地错位、星散布局缺乏整合、重复布局分散客流、单体布局缺乏联系等问题.海峡西岸旅游产业结构布局调整应集中精力抓准重点,延长产业链,设计旅游精品,调整布局构建多级布局体系.  相似文献   
15.
本文以中国、日本、韩国电力体制改革实践为比较对象,从改革的起点、目标的选择、引入竞争的方式、电力监管、电力民营化、改革的成效几个角度进行了分析,力求得到一些对深化中国电力市场化改革有意义的启示。  相似文献   
16.
阿勒泰地区位于新疆的最北端,与欧亚草原之间存在丰富的文化交流,而冶金技术的发展与人类文明紧密相关,为探究新疆阿勒泰地区的冶金发展情况,选取9件草原游牧文化的代表性器物——铜鍑和马具,使用金相显微镜、扫描电子显微镜和X射线能谱仪及双通道电感耦合等离子体发射光谱仪,对16个样品进行金相组织分析和成分分析,并探讨其制作技术特征。研究发现阿勒泰地区的早期铁器时代铜器普遍采用范铸工艺,其成分主要为红铜、砷铜、铅砷青铜。该分析结果为研究新疆阿勒泰地区的冶金发展提供了重要参考。  相似文献   
17.
This paper is the outcome of a lecture held at the Institute of Archaeology, University College London. It provides a summary in English of the archaeozoological research work which has been carried out in Central Europe during the last 30 years, with special reference to material from medieval times. It is shown that a thorough zoological analysis of bones from excavations provides much information for historical interpretation. Not only was the ratio of wild and domestic animals or of the different species of interest, but also the age and sex structure of the population by taking the function of the site into consideration. Some observations on animal teeth gave indications of distinctive handicrafts. Cut marks on cervical vertebrae of horse skeletons found as grave goods from early medieval times were considered in connection with beliefs and juridical conceptions of that time.  相似文献   
18.
Lee, D.-C. February 2017. Radialimbricatus, a new ichnogenus from the lacustrine sandstone facies of the Lower Cretaceous Jinju Formation, South Korea. Alcheringa XX, XXX–XXX.

The trace fossil Radialimbricatus igen. nov. with type species of R. bitoensis isp. nov. occurs in river-mouth-bar sandstone beds of a lacustrine sequence of the Lower Cretaceous Jinju Formation in South Korea. Radialimbricatus is a horseshoe-shaped or elliptical, convex hyporelief structure characterized by imbrication of traces with radial ridges and a median furrow. These features differentiate Radialimbricatus from arthropod ichnofossils such as Rusophycus and Cruziana, possibly cnidarian ichnofossils such as Astropolichnus and vermiform organism ichnofossils such as Oldhamia. Cross-sectional features of R. bitoensis, including upward mud protrusions at lateral margins, demonstrate that R. bitoensis can be formed as an open epigenic furrow at the water/mud interface or an endogenic burrow along the sand/mud interface at the same time. Analysis of discrete and imbricating horseshoe-shaped traces indicates that the tracemaker maintained an obligate inclined posture even when forming trails. The radial ridges and pit along the median furrow are interpreted to reflect feeding behaviour, and the imbrication to result from unidirectional and more or less regular movements to next feeding sites. The tracemaker is thought to have been an organism with an elliptical body outline, radially arranged body parts at the base of or around the body (probably for collecting and transporting foods and moving to feeding sites) and a mouth near the centre of the body, which is consistent with body plan features of arthropods, cnidarians and annelids.

Dong-Chan Lee [], Department of Earth Sciences Education, Chungbuk National University, Cheongju, 28644, South Korea.  相似文献   

19.
20.
This paper analyzes the influence of transportation infrastructure, and in particular of the Regional Express Rail (RER), on employment and population growth in the Paris metropolitan area between 1968 and 2010. In order to make proper causal inference, we rely on historical instruments and control for all other transportation modes that could be complement or substitute to the RER. Our results show that proximity to an RER station increases employment and population density and, in particular, employment and population growth. The latter effects are higher in municipalities located near RER stations and close to employment (sub)centers. They are also found to be particularly strong for jobs in the service sector, for factory workers, and for highly educated population. We find no impact of the RER expansion on employment growth during the first part of the period, while the effect on population growth appears earlier but declines over time.  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