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   1507篇
  免费   167篇
  国内免费   124篇
测绘学   62篇
大气科学   125篇
地球物理   193篇
地质学   392篇
海洋学   124篇
天文学   13篇
综合类   93篇
自然地理   796篇
  2024年   7篇
  2023年   22篇
  2022年   86篇
  2021年   79篇
  2020年   80篇
  2019年   58篇
  2018年   60篇
  2017年   77篇
  2016年   64篇
  2015年   60篇
  2014年   83篇
  2013年   107篇
  2012年   68篇
  2011年   69篇
  2010年   72篇
  2009年   74篇
  2008年   76篇
  2007年   91篇
  2006年   74篇
  2005年   70篇
  2004年   77篇
  2003年   55篇
  2002年   47篇
  2001年   40篇
  2000年   40篇
  1999年   41篇
  1998年   21篇
  1997年   21篇
  1996年   15篇
  1995年   7篇
  1994年   12篇
  1993年   3篇
  1992年   7篇
  1991年   4篇
  1990年   4篇
  1989年   3篇
  1988年   5篇
  1987年   6篇
  1986年   5篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
排序方式: 共有1798条查询结果,搜索用时 562 毫秒
501.
在分析1996~2004年福州市城市化发展和土地利用动态变化的基础上,探求城市化与土地利用变化之间的内在关系,然后选取代表性指标对建设用地和耕地数量与各自的驱动变量进行相关性分析,最后构建了驱动模型。结果表明:(1)1996-2004年,福州市土地利用结构变化明显,土地利用空间变化较大;(2)地均GDP的提高、GDP总量和全社会固定资产投资额的增长是建设用地拓展的主要驱动力;(3)耕地变化的最主要驱动力则是建设用地占用、粮食播种面积和耕地保护政策强度。  相似文献   
502.
Human Losses Expected in Himalayan Earthquakes   总被引:1,自引:1,他引:0  
Quantitative estimates of potential losses that may be caused by future great earthquakes along the Himalaya suggest that as many as 150,000 people may die, 300,000 may be injured and typically 3,000 settlements will be affected in a single event. Scenario results used here vary and are based on ruptures of 150 km segments of the plate boundary at seven positions, where sufficient elastic energy is believed to be stored for magnitude eight earthquakes. The method of calculating these results was calibrated, using the 17 disastrous Indian earthquakes, which have occurred since 1980. About 50 settlements in the region are considered most at risk because in each more than 2000 fatalities may occur.  相似文献   
503.
Climate of Yunnan Plateau is mainly controlledby the system of southwest Asian monsoon, and alsoaffected by westerlies and local climate of the Qing-hai-Tibet Plateau. Since the Cenozoic, a large numberof structural lake basins have formed with the uplift ofthe Qinghai-Tibet Plateau[1]. As the information aboutthe climate and environment change was faithfullydocumented in lake sediments, which have the char-acteristics of continuity, high resolution, abundant in-formation, lake sediments p…  相似文献   
504.
Since 1986, with a sharp decrease in water dis-charges, the Yellow River has entered a period charac-terized by low discharges and seasonally occurring dry-ups[1,2]. Since 1999, more strict management of water diversion has been imposed, and therefore the dry-ups have been well under control. However, the lower reaches of the Yellow River is still predominated by low-discharges, and has become a man-induced shrinking river. In the past 40 years, significant effect of soil and water conservat…  相似文献   
505.
506.
地震人员伤亡估算方法研究   总被引:19,自引:1,他引:18  
本文将目前国内外地震人员伤亡的评估方法区分为将生命损失用货币单位来衡量和单独估算人员伤亡数量两大类,并对评估方法进行了系统归纳总结,在此基础上,利用以倒塌率为主要影响因素的6种估算方法对1976年唐山地震,1996年云南丽江7.0级地震及内蒙古包头西6.4级地震的人员伤亡进行了评估,并与三次地震人员伤亡的实际统计结构进行了比较,最后,提出了一种较精确,适用的伤亡评估方法。  相似文献   
507.
508.
This study investigates the sediment fluxes through the Yellow River sediment routing system, which are among the largest in the world, by constructing a sediment budget of the system over the period from 1855 to 1968. The framework of the sediment budget includes four functional units with the upper and middle reaches of the river as the sediment source and its lower reaches, its delta, and the deep sea as the sediment sinks. Sediment yield from the source and amounts of deposition in the lower Yellow River and the modern Yellow River delta were estimated for completing the sediment budget. The sediment budget produced for the period from 1855 to 1968 was characterized by a sediment input of 1.837 × 1011 tonnes and a distribution of the sediment between the lower Yellow River, the delta, and the deep sea of 64%, 33%, and 3%, respectively. The details of the sediment budget show that the importance of sedimentation in the lower Yellow River changed greatly with variations in the condition of the dykes and other human activities. A comparison of the sediment budgets of the delta for different timescales shows that the proportion of sediment dispersed to the deep sea decreases as the timescale over which the sediment fluxes are investigated increases.  相似文献   
509.
Impacts of human activities on climate change as simulated by the general circulation models (GCMs)in China for the recent ten years have been summarized and reviewed in this paper.The researches show that it might be getting warmer over China due to the greenhouse effects.The atmospheric circulation and precipitation also might be changed due to the greenhouse effects.The assessments and evaluations of the models over the globe and China have also been presented in this paper.  相似文献   
510.
跨世纪的十大人为环境灾难及其对策   总被引:4,自引:0,他引:4  
过去的100年,社会生产力飞速发展,人口急剧增加,人类不合理的生产活动和生活活动,严重地破坏了自身的生存环境,造成了全球性的十大生态灾难,且愈演愈烈,以至危及人类的发展乃至生存。研究十大环境灾难的、现状及其危害,唤起全人类强烈的环保意识,探求合理途径,采取有效措施,防治环境问题,使人类和环境协调发展,是新世纪赋予给人类首要的、刻不容缓的最重要的使用。  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