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   108篇
  免费   6篇
  国内免费   4篇
安全科学   5篇
环保管理   32篇
综合类   57篇
基础理论   10篇
评价与监测   3篇
社会与环境   7篇
灾害及防治   4篇
  2023年   2篇
  2022年   3篇
  2021年   3篇
  2020年   1篇
  2018年   1篇
  2017年   1篇
  2016年   4篇
  2015年   2篇
  2014年   3篇
  2013年   1篇
  2012年   8篇
  2011年   6篇
  2010年   1篇
  2009年   14篇
  2008年   6篇
  2007年   9篇
  2006年   6篇
  2005年   2篇
  2004年   2篇
  2003年   4篇
  2002年   4篇
  2001年   2篇
  2000年   4篇
  1999年   5篇
  1998年   2篇
  1997年   4篇
  1996年   4篇
  1994年   3篇
  1993年   3篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   2篇
  1980年   1篇
  1978年   1篇
排序方式: 共有118条查询结果,搜索用时 234 毫秒
71.
鄂尔多斯白垩系环河含水岩组中的地球化学反向模拟   总被引:1,自引:0,他引:1  
在了解鄂尔多斯盆地的地形、地势、地貌、新构造运动、岩石类型、岩性构造和其他特征的基础上,运用化学热力学原理、质量作用定律和质量守恒定律,用反向模拟的方法对白垩系环河组地下水进行了水-岩作用的地球化学模拟。对该区地下水的演化过程进行了定量的分析研究,揭示了其水化学场的形成机理,总结了矿物的溶解沉淀规律,为该区水文地质模型的建立、地下水资源的水质水量评价及其合理开发利用和科学管理提供了科学依据,可供该地区水土流失等地质灾害的预防和综合治理参考。  相似文献   
72.
Recent studies on the ant phylogeny are mainly based on the molecular analyses of extant subfamilies and do not include the extinct, only Cretaceous subfamily Sphecomyrminae. However, the latter is of major importance for ant relationships, as it is considered the most basal subfamily. Therefore, each new discovery of a Mesozoic ant is of high interest for improving our understanding of their early history and basal relationships. In this paper, a new sphecomyrmine ant, allied to the Burmese amber genus Haidomyrmex, is described from mid-Cretaceous amber of France as Haidomyrmodes mammuthus gen. and sp. n. The diagnosis of the tribe Haidomyrmecini is emended based on the new type material, which includes a gyne (alate female) and two incomplete workers. The genus Sphecomyrmodes, hitherto known by a single species from Burmese amber, is also reported and a new species described as S. occidentalis sp. n. after two workers remarkably preserved in a single piece of Early Cenomanian French amber. The new fossils provide additional information on early ant diversity and relationships and demonstrate that the monophyly of the Sphecomyrminae, as currently defined, is still weakly supported.  相似文献   
73.
Deinonychosaurian theropods, the dinosaurian sister group of birds, are characterized by a large raptorial claw borne on a highly modified second digit that was thought to be held in a retracted position during locomotion. In this study, we present new trackway evidence for two coeval deinonychosaurian taxa from the Early Cretaceous of Shandong, China that indicate a hitherto unrecognized body size diversity for this period and continent. These fossil tracks confirm diversity and locomotory patterns implied by phylogeny and biogeography, but not yet manifested in the body fossil record. Multiple parallel and closely spaced trackways generated by the larger track maker provide the best evidence yet discovered for gregarious behavior in deinonychosaurian theropods.  相似文献   
74.
The reduced lower temporal arcade of the skull and the movable quadrate are the most distinctive features of squamates. Up to now, no exception has been documented for any fossil or extant squamates. We report here a new fossil lizard that possesses a complete lower temporal arcade and an unmovable quadrate. The anatomical relationships indicate that those two modifications were secondarily obtained in the new lizard. The complete lower temporal bar and the firm contact between the pterygoid and quadrate may have served as a brace to support the quadrate jaw articulation and thus prevent it from twisting anteriorly rather than posteriorly during the bite cycles. This represents an entirely new pattern of jaw muscle functions within the Squamata.  相似文献   
75.
Across a spectrum of contemporary contexts from public health to landscape ecology and natural resources, there is need for objective determination of elevated occurrence in phenomena such as disease incidence and biodiversity. Occurrences of such phenomena constitute response surfaces, but data regarding the surface is typically acquired in a cellular framework. The cells may comprise a regular grid, or may be of irregular shapes such as counties in which statistics are collected. Echelons are a topologically based approach to systematic determination of spatial structure in a step surface. Spatial scan statistics are a probability-based approach to the same issue when interest lies in a rate variable. Here we examine the use of echelons both separately and in conjunction with the SaTScan implementation of spatial scan statistics for purposes of determination and visualization of upper-level sets. Consideration is given to both conventional geographic space and to the cellular pseudo-space of contingency tables for ordered categorical variables. Received: August 2002 / Revised: July 2005  相似文献   
76.
浙东沿海上白垩统小雄组的建立   总被引:1,自引:0,他引:1  
浙东临海、三门东部的小雄盆地,发育一套中酸偏碱性的火山岩。长期以来,将其称为塘上组。详细的地质调查研究表明;这套火山岩与以天台盆地为代表的塘上组,在火山岩岩石组合、层序、古生物化石组合和同位素年龄等均不相同。火山岩是超覆于永康群馆头组、朝川组和小平田组之上,成岩时代在85—98Ma,产晚白垩世翼龙和鸟类化石,是晚白世的喷发一沉积产物。为一独立的具有自身特色的岩石地层单位,故建立新的岩石地层单位一小雄组。  相似文献   
77.
浙东宁波盆地白垩纪陆相火山岩系,经古地磁研究表明,以往认为时代属于早白垩世早期的馆头组,晚期朝川组和晚白垩世早期的方岩组均呈正向磁化,平均磁化方向基本一致。据绝对年龄和古生物旁证,磁化时间属白垩纪中期正向极性超时。因此,馆头组的层位应作相应的提高,从白垩系下部上升到白垩系中部;朝川组随之位于其上。方岩组纳入白垩系中部,在馆头组之下还应有一套以正负极性交迭为特征的白垩纪早期沉积物。从而对以往所谓的上侏罗统磨石山群的时代提出疑问。从古地磁方向特征的规律,支持了白垩系三分说。  相似文献   
78.
79.
基于Web-GIS的黄浦江上游水源地突发水污染事故预警系统   总被引:1,自引:0,他引:1  
针对黄浦江上游可能发生的突发性水污染事故,建立了油品、化学品理化性质数据库和特征流场数据库,开发了基于Web浏览器环境的突发水污染事故预警系统。通过该系统,用户可以使用Web浏览器在线模拟和统计分析突发的水污染事故,及时有效地掌握水污染现状及发展趋势,为决策者提供技术支持。该系统提供了灵活方便的操作界面,所有的空间数据分析和模拟运算全部在服务端实现,客户端只负责请求操作、模拟结果的动态显示和统计分析,便于系统的整体维护与升级。  相似文献   
80.
New material of the enigmatic diapsid Khurendukhosaurus is described from the Mongolian type locality, Khuren Dukh, providing additional data on the vertebral column, pelvis, and hind limb. It confirms the choristoderan status of the genus and permits a more detailed phylogenetic analysis that supports a relationship between Khurendukhosaurus and the long-necked Asian Hyphalosauridae. The existence of tall caudal neural spines implies that Khurendukhosaurus was a deep-tailed swimmer. This and the open sacral costocentral sutures suggest a primarily aquatic lifestyle. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Institutional abbreviations  MNHN BL, Museum National d’Histoire Naturelle, Paris, France; MPC, Mongolian Paleontological Center; PIN, Paleontologicheski Institut, Akademii Nauk, Moscow; HMNS, Hayashibara Museum of Natural Sciences, Okayama, Japan.  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