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   419篇
  免费   8篇
  2024年   3篇
  2023年   6篇
  2022年   8篇
  2021年   12篇
  2020年   13篇
  2019年   16篇
  2018年   8篇
  2017年   16篇
  2016年   14篇
  2015年   10篇
  2014年   14篇
  2013年   45篇
  2012年   23篇
  2011年   22篇
  2010年   13篇
  2009年   19篇
  2008年   19篇
  2007年   31篇
  2006年   25篇
  2005年   21篇
  2004年   8篇
  2003年   18篇
  2002年   17篇
  2001年   11篇
  2000年   14篇
  1999年   4篇
  1998年   4篇
  1997年   1篇
  1996年   1篇
  1994年   4篇
  1993年   3篇
  1991年   2篇
  1988年   1篇
  1983年   1篇
排序方式: 共有427条查询结果,搜索用时 15 毫秒
1.
2.
湘南地区毗邻赣、粤、桂三省,地理位置特殊,是一个复杂的地理单元。及至清代,湘南地区已是湖南省乃至全国铜、铅、银等矿业生产的主要区域。长达数百年的矿产开采与冶炼,促进了地方社会的经济发展,也给当地的生态环境带来深远影响。由此,湘南官绅民各界对矿业开发引发的环境问题亦有因应,“坑冶十害论”和“九嶷山封禁案”即为其集中体现。开矿采砂本为解决贫民生计而采取的措施,但因破坏风水、污染水土等一系列影响环境的后果,以致出现开矿与禁矿之争,使得湘南地区矿业开发一度出现波折。这两例个案亦折射出在“重本抑末”的传统社会中地方官绅士民在生计与风水之间的离合关系。地方社会以保护风水为由严禁矿冶,在一定程度上遏止了生态环境的破坏与恶化,不过,其在环保方面发挥的作用也不宜被高估。  相似文献   
3.
Recent fieldwork has considerably increased our knowledge of early Holocene settlement in Southwest Arabia. Neolithic settlement occurred within an environmental context of increased monsoonal moisture that continued during the mid-Holocene. A now well-attested Bronze Age exemplified by village- and town-scale settlements occupied by sedentary farmers developed toward the end of the mid-Holocene moist interval. The high plateau of Yemen was an early focus for the development of Bronze Age complex society, the economy of which relied upon terraced rain-fed and runoff agriculture. On the fringes of the Arabian desert, the precursors of the Sabaean literate civilization have been traced back to between 3600 and 2800 B.P., and even earlier, so that a virtually continuous archaeological record can now be described for parts of Yemen. In contrast to the highlands these societies relied upon food production from large-scale irrigation systems dependent upon capricious wadi floods. Bronze Age settlement, while showing some links with the southern Levant, now shows equal or stronger linkages with the Horn of Africa across the Red Sea. Although some regions of Yemen show breaks in occupation, others show continuity into the Sabaean period when a series of major towns grew up in response to the incense trade with the north. It is now clear that these civilizations grew up on the foundations of earlier Bronze Age complex societies.  相似文献   
4.
The Hui-style residence is an important architectural heritage of China. The hollow wall structures are widely used to build its exterior wall system. However, the thermal performance of the hollow wall is no longer able to meet the new energy-saving and environmental requirement. This article describes a laboratory study of the development of foamed mortar (FM), with the potential for use in thermal upgrading of the Hui-style hollow wall system without dramatically changing its traditional structure. The key early age, physical, mechanical and thermal properties were systematically measured. Two extended models were respectively developed to calculate compressive strength and thermal conductivity, as a function of porosity. Environment chamber test was also employed to investigate the effectiveness of this novel thermal upgrading approach and the results show that filling the voids with FM can effectively improve the overall thermal resistance of the hollow wall system by 44%, which is almost equal to the overall thermal resistance when using the more expensive commercial inorganic stucco system. In addition, the combination of these two methods yielded an overall thermal resistance of 0.701 m2·K/W, which is even higher than 0.67 m2·K/W for the code required in the hot summer/cold winter climate zone.  相似文献   
5.
In this paper, we argue that place mapping is useful for approaching children's conception of place and that this is of relevance when designing physical activity interventions. We contend that socio-material factors influence children's perception and use of places, and are crucial to understand in relation to their use of local neighbourhoods for physical activity. A place mapping of children's understandings and everyday use of their local neighbourhood in suburban Copenhagen was conducted with a fifth grade elementary school class. The mapping and subsequent analysis resulted in three categories of relevance to children's conceptions of place; located social experiences, experiences of the unknown, and children's contested spaces. We argue that such knowledge can provide useful information in the development and evaluation of activities that promote physical activity in urban spaces.  相似文献   
6.
Metallurgical analyses and chemical characterizations were carried out on historical cannonballs from the Fortress of San Juan de Ulúa, Veracruz, México. Cannonballs dating from the 18th and 19th centuries share metallurgical characteristics similar to those of material coming from a shipment of ammunition found in the wreck of a sunken French ship from the battle of Trafalgar. The analyses show that the base material is grey cast iron with a carbon equivalent of 4.94 and a ferritic–perlitic matrix, in which the high phosphorus content has led to the formation of iron phosphide compounds in conjunction with a homogeneous distribution of carbon graphite flakes of Type C. In addition, corrosion products from samples revealed the presence of various crystalline iron compounds (X‐ray diffraction), mostly highly chlorinated iron compounds identified as akaganeite. X‐ray fluorescence identified various characteristics of the corrosion products as a function of the sampling depth. FT–IR spectroscopy revealed that the main difference between the corrosion products (internal and external) is determined by the number of organic species. Differential scanning calorimetry corroborated that these corrosion products are thermally stable compounds at elevated temperatures.  相似文献   
7.
The advertising of unhealthy food and beverages forms an important component of obesogenic environments. Such marketing to children is a key health determinant because of its impact on dietary preference and food purchasing behaviour. The location of outdoor advertising is important in exploring obesogenic environments and children's neighbourhoods. The aim of this study is to explore issues involved in the use of Google Street View to examine outdoor food and beverage advertising. The implications for using Google Street View in the context of neighbourhood built environment research and grass‐roots advocacy are discussed. The study was conducted within walkable distances from 19 primary and intermediate schools in Auckland, New Zealand, where “walkable” was defined as limited by 800 m road network boundaries, which are equivalent to school buffer boundaries. Google Street View allows for centrality of data collection, coding, and storage. However, challenges exist with the method because 727 (29.4%) of a total of 2,474 outdoor advertisements that were identified were not able to be categorised because images were unclear, not in English, blocked, or at angles where detail cannot be deciphered. Specific to outdoor advertising for food and beverages, the results presented here show that children are exposed to a significantly greater number of unhealthy advertising than other advertising, P=0.001, eta‐squared statistic (0.45) indicates a large effect size. Overall, the results show promise for the use of Google Street View in the study of obesogenic environments.  相似文献   
8.
为了探索一种适宜的遗址文物保存方式,在四季分明,气候变化较为剧烈的西北地区的文物遗址环境区,达到最大程度保护遗址文物的目的,通过对开放式的秦始皇兵马俑博物馆一号坑遗址环境的建筑结构、温度和相对湿度变化及大气颗粒物进行分析监测,并与封闭式汉阳陵博物馆外葬坑的结果进行对比研究,发现单从环境温湿度恒定、阻挡室外颗粒污染物和气态污染物的角度来讲,封闭式的汉阳陵博物馆存在明显的优势。但依然不能阻止温湿度的季节间波动和室外空气污染物渗入的威胁,同时还要预防室内污染的发生,并且出现玻璃护围内部结露,文物大面积返碱等问题,并不能很好解决文物良好保存和观展目的。所以依旧需要探索一种适宜的遗址文物保存方式,既能保持文物保存环境的温湿度的相对稳定和洁净,又能缓解全封闭玻璃护围内部结露,文物大面积返碱等问题,最大程度延长遗址文物的寿命的同时,满足观众参观的需求。本对比研究结果可为今后的设计提供参考。  相似文献   
9.
王晗  郭平若 《史学月刊》2007,1(4):86-93
陕北长城外地区位于蒙陕农牧交错带,属于典型的脆弱生境地带。清代中央和地方两级政府针对当地汉民承租蒙民土地从事农牧业生产这一环节,在不同时期制定了不同的垦殖政策,经历了封禁、招垦、禁垦、拓垦四个阶段,这既是清政府对陕北长城外地区逐步认识和开发的过程,同时也是该地区生态环境变化的过程。在政策—人—环境相互作用的关系过程中,制度、政策与权力的结合对区域环境变化的影响具有根本性的驱动作用。  相似文献   
10.
关于利用历史文献信息进行环境演变研究的几点看法   总被引:1,自引:0,他引:1  
针对如何更好地利用我国丰富的历史文献记录,开展历史时期环境演变研究,本文提出四点看法:从地球系统科学与全球变化研究的前沿中寻找研究的主题,在诸多不确定中寻找确定性答案,构建历史文献信息共享的环境演变研究平台,培养文理兼备的复合型人才。  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