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   291篇
  免费   16篇
  国内免费   24篇
测绘学   48篇
大气科学   21篇
地球物理   28篇
地质学   98篇
海洋学   27篇
天文学   78篇
综合类   22篇
自然地理   9篇
  2024年   2篇
  2023年   2篇
  2022年   2篇
  2021年   4篇
  2020年   6篇
  2019年   8篇
  2018年   6篇
  2017年   8篇
  2016年   9篇
  2015年   9篇
  2014年   16篇
  2013年   9篇
  2012年   14篇
  2011年   13篇
  2010年   10篇
  2009年   16篇
  2008年   21篇
  2007年   18篇
  2006年   16篇
  2005年   10篇
  2004年   19篇
  2003年   9篇
  2002年   11篇
  2001年   6篇
  2000年   17篇
  1999年   11篇
  1998年   13篇
  1997年   4篇
  1996年   1篇
  1995年   4篇
  1994年   2篇
  1992年   1篇
  1991年   1篇
  1989年   2篇
  1987年   1篇
  1985年   1篇
  1927年   1篇
  1921年   1篇
  1919年   1篇
  1915年   1篇
  1905年   3篇
  1900年   3篇
  1897年   7篇
  1882年   1篇
  1880年   2篇
  1877年   6篇
  1875年   3篇
排序方式: 共有331条查询结果,搜索用时 0 毫秒
81.
We present data for the concentrations of eleven rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu) in eleven international geochemical reference materials obtained by isotope dilution multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). We have analysed both rock powders and synthetic silicate glasses, and the latter provide precise data to support the use of these as reference materials for in situ trace element determination techniques. Our data also provide precise measurements of the abundance of mono-isotopic Pr in both glasses and powders, which allows more accurate constraints on the anomalous redox-related behaviour of Ce during geochemical processes. All materials were analysed in replicate providing data that typically reproduce to better than one percent. Sm/Nd ratios in all these materials also reproduce to better than 0.2% and are accurate to < 0.2% and can thus be used as calibrants for Sm-Nd geochronology. Our analyses agree well with existing data on these reference materials. In particular, for NIST SRM 610, USGS BHVO-2, AGV-1 and AGV-2, our measured REE abundances are typically within < 2% (and mostly 1%) of REE concentrations previously determined by isotope dilution analysis and thermal ionisation mass spectrometry, consistent with the higher degree of precision and accuracy obtained from isotope dilution techniques. Close agreement of results between basaltic glass reference materials USGS BHVO-2G and BCR-2G and the BHVO-2 and BCR-2 powders from which they were created suggests that little fractionation, concentration or dilution of REE contents occurred during glass manufacture.  相似文献   
82.
结合工作实际及3G无线网络规划的业务需求,简要阐述了3G无线网络规划中空间地理信息数据的建设过程、网络规划各阶段中地理信息数据的应用及GIS的发展前景。  相似文献   
83.
本研究基于5G技术的实时三角测绘在测绘信息中的应用案例.通过瀑布式开发模型,本文在明确使用三角控制测量法的前提下,使用5G技术及其带来的分布式计算技术和自适应组网技术,对基于5G技术的实时沉降三角测绘系统进行了开发,通过组网测试,发现该系统的测量精度与使用全站仪人工测量精度相当,且系统部署过程并未对原有的IDC核心节点...  相似文献   
84.
3G技术4D集成在云南边防信息系统中的应用   总被引:2,自引:1,他引:2  
讨论了 4D集成的空间数学框架、空间与非空间数据库组织方式、数据模型设计以及 3G技术结合的可能性与可行性 ,并介绍了其在云南边防信息系统中的集成及应用情况。  相似文献   
85.
The aim of this study was to map soil erosion on the Mediterranean island of Cyprus. The G2 model, an empirical model for month-time step erosion assessments, was used. Soil losses in Cyprus were mapped at a 100?m cell size, while sediment yields at a sub-basin scale of 0.62?km2 mean size. The results indicated a mean annual erosion rate of 11.75?t?ha?1?y?1, with October and November being the most erosive months. The 34% of the island's surface was found to exceed non-sustainable erosion rates (>10?t?ha?1?y?1), with sclerophyllous vegetation, coniferous forests, and non-irrigated arable land being the most extensive non-sustainable erosive land covers. The mean sediment delivery ratio (SDR) was found to be 0.26, while the mean annual specific sediment yield (SSY) value for Cyprus was found to be 3.32?t?ha?1?y?1. The annual sediment yield of the entire island was found to be 2.746?Mt?y?1. This study was the first to provide complete and detailed erosion figures for Cyprus at a country scale. The geodatabase and all information records of the study are available at the European Soil Data Centre (ESDAC) of the Joint Research Centre (JRC).  相似文献   
86.
基于GIS交通网络的室内3维网络模型研究   总被引:1,自引:0,他引:1  
在2维交通网络逻辑数据模型基础上,讨论了概念化的楼层网络,进行了室内连通的3维网络模型的研究。基于ArcGIS的交通网络模型建立了试验区的室内3维网络模型.并给出分析结果,该方法为室内3维网络模型研究提供了技术支持。  相似文献   
87.
A rapidly deployable dense seismic monitoring system which is capable of transmitting acquired data in real time and analyzing data automatically is crucial in seismic hazard mitigation after a major earthquake. However, it is rather difficult for current seismic nodal stations to transmit data in real time for an extended period of time, and it usually takes a great amount of time to process the acquired data manually. To monitor earthquakes in real time flexibly, we develop a mobile integrated seismic monitoring system consisting of newly developed nodal units with 4G telemetry and a real-time AI-assisted automatic data processing workflow. The integrated system is convenient for deployment and has been successfully applied in monitoring the aftershocks of the Yangbi MS 6.4 earthquake occurred on May 21, 2021 in Yangbi County, Dali City, Yunnan in southwest China. The acquired seismic data are transmitted almost in real time through the 4G cellular network, and then processed automatically for event detection, positioning, magnitude calculation and source mechanism inversion. From tens of seconds to a couple of minutes at most, the final seismic attributes can be presented remotely to the end users through the integrated system. From May 27 to June 17, the real-time system has detected and located 7 905 aftershocks in the Yangbi area before the internal batteries exhausted, far more than the catalog provided by China Earthquake Networks Center using the regional permanent stations. The initial application of this integrated real-time monitoring system is promising, and we anticipate the advent of a new era for Real-time Intelligent Array Seismology (RIAS), for better monitoring and understanding the subsurface dynamic processes caused by Earth's internal forces as well as anthropogenic activities.  相似文献   
88.
在中高渗油藏的水驱开发过程中,由于水流的长期冲刷作用,储层岩石的部分颗粒发生运移,伴随着油井出砂储层大孔道逐渐发育,边底水或注入水无效循环严重,影响油藏的开发效果.以高浅北区G104-5区块高渗透稠油油藏为例,基于现场油水井生产特征优选了10个评价大孔道发育程度的动静态指标参数,应用层次分析法确定指标权重;综合考虑油水...  相似文献   
89.
90.
为了寻找并克隆凡纳滨对虾(Litopenaeus vannamei)G蛋白α亚基,为研究对虾的生理调控提供理论基础,通过简并PCR和RACE反应获得目的基因的全长cDNA序列;用Blast, DNAstar和Genedoc软件对所得序列进行分析,确定所得序列为凡纳滨对虾G蛋白Gαq基因,命名为pvGαq.将该基因的编码序列克隆到表达载体,通过免疫共沉淀实验和胞内Ca2 , IP3浓度的测定鉴定该Gαq亚基的功能,发现该亚基的序列和功能与其他Gαq家族成员具有高度保守性.用Western blotting分析发现pvGαq在对虾身体各部位存在普遍分布,尤其在脑神经、眼柄、腮和颚片中有大量表达,在嗅觉器官触角也有适量分布.说明了pvGαq在对虾生命活动中的重要性,为研究对虾的生理调控奠定了理论基础.  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