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   52137篇
  免费   8485篇
  国内免费   11650篇
测绘学   4639篇
大气科学   5796篇
地球物理   10460篇
地质学   30840篇
海洋学   5982篇
天文学   2181篇
综合类   3568篇
自然地理   8806篇
  2024年   329篇
  2023年   804篇
  2022年   1571篇
  2021年   1790篇
  2020年   1855篇
  2019年   2065篇
  2018年   1663篇
  2017年   1955篇
  2016年   2150篇
  2015年   2269篇
  2014年   2842篇
  2013年   2819篇
  2012年   3065篇
  2011年   3232篇
  2010年   2814篇
  2009年   3286篇
  2008年   3276篇
  2007年   3609篇
  2006年   3479篇
  2005年   3038篇
  2004年   2834篇
  2003年   2692篇
  2002年   2462篇
  2001年   2097篇
  2000年   1963篇
  1999年   1808篇
  1998年   1568篇
  1997年   1416篇
  1996年   1292篇
  1995年   1079篇
  1994年   1125篇
  1993年   951篇
  1992年   756篇
  1991年   528篇
  1990年   468篇
  1989年   373篇
  1988年   287篇
  1987年   191篇
  1986年   128篇
  1985年   81篇
  1984年   35篇
  1983年   30篇
  1982年   30篇
  1981年   21篇
  1980年   23篇
  1979年   28篇
  1978年   38篇
  1977年   25篇
  1975年   4篇
  1954年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This paper presents an integrated measurement technique based on DC methods (vertical electrical sounding, electrical resistivity tomography) which was used to identify faults and determine their geoelectric parameters in the western part of the Chuya basin. New information on the structure of the Chagan River valley located in the zone of the disastrous 27 September 2003 Chuya earthquake has been obtained from the results of these methods. Geoelectric cross-sections of the sedimentary sequence and the upper part of the basement were obtained from VES data, showing the block structure of the study area. Electrical resistivity tomography sections confirm the presence of a major fault between basement blocks of different heights and indicate the presence of faults bounding the valley on its right side and in the southwestern part.  相似文献   
62.

采用湖南14个地市州所在地国家气象站1980—2013年逐分钟降雨资料, 分别利用模糊识别法、芝加哥法、Pilgrim & cordery法及同频率法对各地短历时60 min、90 min、120 min、150 min、180 min以5 min为单位时段的暴雨雨型进行了识别和推求, 结果表明:推求的各地暴雨雨型基本以峰值在前部的单峰型为主; 芝加哥、Pilgrim & cordery计算的峰值、强度相当, 推求的各历时暴雨雨型基本一致, 也更接近实际, 同频率法相对来说效果较差些。

  相似文献   
63.
Diaspora engagement is a growing trend and many governments, international organisations and policy makers are increasingly focusing on the role of diaspora in development strategies for the homelands. Such policies are predominantly critical to island-dense regions such as the Caribbean and Pacific that have suffered high rates of outmigration during the postcolonial period. One such Pacific island is Pitcairn, a British Overseas Territory, and is the focus of this article. But while most of the literature focuses on the positive benefits of diaspora engagement, this paper examines the dynamics of diaspora (dis)engagement and (dis)affection. Each diaspora has a unique set of needs and capabilities based on its historical experience and the present realities of its countries of origin and destination. While much has been written celebrating the role of diasporas in development, diaspora have also shown themselves to have dual natures, with sometimes conflicting identities and allegiances. Based on analysis of a recent Pitcairn Diaspora Survey and ethnographic data, discussion in this paper reveals that the best intentions of engaging diaspora for development can be impeded by several factors including: (1) the complex nature of identity, place and politics; (2) difficult negotiations between past, present and future intentions of movers; and (3) shifting ‘roots/routes’ and boundaries of identification. Consequently, the paper aims to highlight the realities of settlement and relationships of diaspora space and subjectivity with the homeland.  相似文献   
64.
李军 《地理空间信息》2009,7(5):155-156
对于测绘技术人员来说,需要编写设计书、技术总结、监测方案等测绘类文档。利用Word2003自带的绘图工具,远远不能满足要求。介绍了“利用复制+粘贴工具”、“转换图像格式”、“使用插入对象”三种方式在Word2003文档中插入AutoCAD2004图形的三种方法,  相似文献   
65.
Herein we investigate the coupled orbital and rotational dynamics of two rigid bodies modelled as polyhedra, under the influence of their mutual gravitational potential. The bodies may possess any arbitrary shape and mass distribution. A method of calculating the mutual potential’s derivatives with respect to relative position and attitude is derived. Relative equations of motion for the two body system are presented and an implementation of the equations of motion with the potential gradients approach is described. Results obtained with this dynamic simulation software package are presented for multiple cases to validate the approach and illustrate its utility. This simulation capability is useful both for addressing questions in dynamical astronomy and for enabling spacecraft missions to binary asteroid systems.  相似文献   
66.
李争辉  罗亚丽 《暴雨灾害》2021,41(2):101-110

利用1980—2017年华南地区303个国家级地面气象站逐小时降水数据、ERA-Interim再分析资料,分析华南前汛期(4—6月)降水统计特征,定义站点上短时(1—6 h)、中等时长(7—12 h)和长时(>12 h)降水事件,对比降水量、频次和强度在南海季风爆发前后的变化,以及所定义的西部内陆、东部内陆、沿海地区的异同。结果表明:(1)南海季风爆发后,研究区域平均而言,三类降水事件的降水量增多、小时降水强度增强,短时、长时降水事件发生频次增多,而中等时长降水事件发生频次有所减少。(2)从空间分布来看,南海季风爆发后,小时降水强度在整个华南地区均增强,西部内陆时长大于6 h的降水事件尤为明显;降水事件的发生频次在西部内陆和沿海地区升高,而东部内陆时长大于6 h的降水事件发生频次降低,因此,季风爆发后西部内陆和沿海地区的总降水量均显著增大,而东部内陆的总降水量变化不大。(3)西部内陆降水事件主要在夜间开始发生,持续时间越长的事件越早开始,且由西向东逐渐推迟;东部内陆短时降水事件主要在14时(北京时,下同)左右开始,季风爆发后更为明显,而时长大于6 h的降水事件的开始时间和峰值时间无明显的分布规律;沿海地区短时降水事件在季风爆发前主要于05—08时开始,季风爆发后,在海岸线约50 km以内仍然如此,而较远离海岸线的短时降水事件主要于14时开始,沿海地区长时降水事件在季风爆发前、后都倾向于在夜间开始,并在日间出现峰值。

  相似文献   
67.
渤海海域渤中凹陷西南部构造复杂,其沉积充填演化规律不明确。综合运用岩芯、测井以及三维地震资料,对该区断陷湖盆古新世—始新世的构造活动、沉积体系以及盆地充填演化规律进行了系统研究。研究表明,渤中凹陷西南部古近纪孔店-沙河街组发育孔店组末期、沙三段末期、沙一二段末期等3期构造活动,多次隆升剥蚀形成3个关键层序界面,控制整个湖盆古近纪孔店-沙河街组的层序结构和古地貌形态。古新世—始新世主要发育近源扇三角洲、辫状河三角洲、湖泊以及湖底扇等4种沉积体系类型,其分布受古物源、古地貌、断裂活动等因素制约。在古新世孔店组沉积裂陷早期,湖盆范围小,物源供给充足,陡坡带和缓坡带均以发育扇三角洲沉积为主,湖盆中心发育湖底扇沉积,晚期湖盆逐渐萎缩;始新世早期的沙三段沉积时期,断陷活动加强,随着盆地范围的扩张,物源供应减弱,湖盆洼陷区主要发育湖底扇沉积。始新世晚期沙一二段裂后沉降期,辫状河三角洲进积特征明显,分布范围广,局部地貌高位置发育湖相碳酸盐岩沉积。不同时期构造差异活动与物源供给共同制约着该区古近纪孔店-沙河街组的沉积充填演化过程,也导致了与渤海海域其他构造区沉积充填的差异性。  相似文献   
68.
The Cultural Impact Assessment of the Saru River Region represents the first time that a site investigation was implemented in Japan in order to preserve an ethnic culture in relation to the construction of a dam. One of the project's basic concepts was to get local residents, especially those of Ainu ethnicity, to participate in the investigation. Existing case studies of environmental impact assessment have argued that the assessment has failed to sufficiently involve Indigenous people in its process and has largely failed to incorporate Indigenous knowledge, cultural values, and voices into its processes and outcomes. Also, intangible aspects of Indigenous cultural heritage have not been protected. In the Cultural Impact Assessment of the Saru River Region, the Final Report was released in 2006 and significantly included the 3 year investigation of input by local residents. In this sense, this assessment succeeded in effectively involving Indigenous people in its process and in reflecting their cultural values in its results. The more important issue is, however, how these results were included in the final outcomes. If Indigenous people have no power over final decision making, their involvement is not effective. This paper analyses the significance and unresolved problems involved in this overall assessment process.  相似文献   
69.
In the assessment of air quality, regional distribution and dispersion with distance are important, together with the variations of pollutants in time. On this occasion, the point cumulative semi-variogram (PCSV) method is used in order to find simply regional distribution of pollutants of Erzurum urban centre. This method is based simply on the summation of square differences in air pollutant concentrations between different sites. Monthly regional variation maps of Erzurum are constructed by finding radius of influence (for SO2, from 1000 m to 3500 m and, for TSP, 1000–2000 m) and PCSV scattering diagram data at different levels by using monthly average sulphur dioxide (SO2) and total suspended particulate (TSP) matter concentrations in 2001–2002 winter season. Consequently, the air pollution distribution of Erzurum is assessed.  相似文献   
70.
在小口径加筋砼灌注桩试桩基础上结合工程实例对小口径加筋砼灌注桩的设计、施工和检测进行了初步探讨  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