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   448篇
  免费   85篇
  国内免费   149篇
测绘学   79篇
大气科学   114篇
地球物理   129篇
地质学   185篇
海洋学   66篇
天文学   6篇
综合类   40篇
自然地理   63篇
  2024年   9篇
  2023年   13篇
  2022年   21篇
  2021年   28篇
  2020年   37篇
  2019年   35篇
  2018年   21篇
  2017年   30篇
  2016年   35篇
  2015年   29篇
  2014年   30篇
  2013年   43篇
  2012年   32篇
  2011年   40篇
  2010年   31篇
  2009年   27篇
  2008年   27篇
  2007年   20篇
  2006年   26篇
  2005年   26篇
  2004年   19篇
  2003年   12篇
  2002年   16篇
  2001年   13篇
  2000年   7篇
  1999年   6篇
  1998年   7篇
  1997年   14篇
  1996年   6篇
  1995年   3篇
  1994年   13篇
  1993年   4篇
  1989年   1篇
  1988年   1篇
排序方式: 共有682条查询结果,搜索用时 0 毫秒
31.
闽台地震速报技术研究   总被引:1,自引:0,他引:1  
本文通过系统地分析台网正式运行以来记录到主要的网内、网缘、网外地震的各种震相特征和定位参数 ,总结研究各区的震相特征、台站记录状况和震级的误差 ,力争提高台网地震速报的速度和精度。  相似文献   
32.
地震速报参数不确定性的应急灾害损失快速评估模型   总被引:7,自引:0,他引:7  
本文针对目前地震应急灾害损失快速评估中存在的问题,建立了考虑地震速报参数不确定性的灾害损失快速评估模型。并利用1990年来全国的81组速报震中与宏观震中数据。得到速报震中与宏观震中偏差的概率分布经验参数。  相似文献   
33.
灰色理论应用于轨道交通一号线一期工程承重墩沉降分析   总被引:1,自引:0,他引:1  
介绍了沉降监测数据处理理论方法,讨论了灰色模型法预测沉降的过程,分析了武汉轨道交通一期工程承重墩沉降监测数据,结果表明其基础是基本稳定的。  相似文献   
34.
???GPS?????λ??????????????????????????????????????????????M??????????????μ??????????????????????????????????????????????е????????????????????????÷??????п???????????????????????????  相似文献   
35.
以平潭综合实验区主岛--海坛岛为研究区,基于 2000、2009 和 2013 年 3 期 SPOT 遥感数据,运用单一土地利用动态度、马尔科夫转移矩阵模型、最近邻点统计量、核密度估计、探索性数据分析和空间“热点”探测方法定量分析海坛岛农村居民点时空分布特征及其演变规律,并从景观生态学角度深入分析农村居民点空间分布特征的影响因素。结果表明:1)2000―2013 年间农村居民点扩张明显,面积共增加 399.69 hm2 ,主要转自耕地和林地,后期(2009―2013 年)的增量、增速均比前期(2000―2009 年)大,说明综合实验区的成立对海坛岛农村居民点扩张产生重要影响。2)海坛岛农村居民点扩展主要形式:一是块状扩展,即沿原有斑块向四周蔓延式向外扩展;二是带状扩展,即沿各乡镇的交通干线向两侧或某侧扩展。3)2000、2009 和 2013 年海坛岛农村居民点的空间分布均表现出显著的聚集特征,呈现高密度小规模集聚分布与低密度大规模集聚分布格局,且随时间变化,农村居民点集聚程度不断提高。4)坡度、地形起伏度、道路和河流等景观要素对海坛岛农村居民点的布局有显著影响,农村居民点主要分布在地势平坦、坡度平缓(0~10°)、近水源(距河流<1 500 m)以及交通便利(距离道路<500 m)的地方,且扩张趋势明显;反之,农村居民点分布明显较少。  相似文献   
36.
Infrastructure owners and operators, or governmental agencies, need rapid screening tools to prioritize detailed risk assessment and retrofit resources allocation. This paper provides one such tool, for use by highway administrations, based on Bayesian belief network (BBN) and aimed at replacing so‐called generic or typological seismic fragility functions for reinforced concrete girder bridges. Resources for detailed assessments should be allocated to bridges with highest consequence of damage, for which site hazard, bridge fragility, and traffic data are needed. The proposed BBN based model is used to quantify seismic fragility of bridges based on data that can be obtained by visual inspection and engineering drawings. Results show that the predicted fragilities are of sufficient accuracy for establishing relative ranking and prioritizing. While the actual data and seismic hazard employed to train the network (establishing conditional probability tables) refer to the Italian bridge stock, the network structure and engineering judgment can easily be adopted for bridges in different geographical locations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
37.
激光加工技术在珠宝首饰业中的应用越来越广泛。介绍了该技术的基本特点以及其在珠宝首饰业中的典型应用现状。这些技术涉及激光焊接、激光快速原型技术、激光打标、激光雕刻和激光切磨钻石等领域。激光焊接比传统的焊接技术具有显著的优点;快速原型技术的引入大大缩短了从首饰图样到制出原版的时间;激光打标和激光雕刻的使用丰富了首饰表面处理的手段,可进一步满足首饰个性化需求;激光切磨钻石原石可达到最小的损耗。激光加工技术在珠宝首饰业中发挥着越来越重要的作用。  相似文献   
38.
Current high‐resolution palaeoenvironmental records reveal short‐term Holocene coolings. One of these major Holocene rapid climate changes occurred between 3.2 and 2.7 cal. ka BP. The sensitivity of river systems vis‐à‐vis slight and short‐term Holocene climatic variations is a subject of controversy in the scientific community. In this paper, we present a 4.0 to 1.4 cal ka BP palaeoflood record from the Lower Moulouya River (northeastern Morocco) to demonstrate the high sensitivity of semiarid rivers in the southwestern Mediterranean towards Holocene environmental changes. The Lower Moulouya flood deposits are characterised by thick, well‐stratified, predominantly clayey to silty overbank fine sediments. These cohesive sediments show evidence of excellent preservation conditions against fluvial erosion and contain a continuous record of mid to late Holocene flood sequences. The Moulouya palaeoflood record can be interpreted in the context of regional and global high‐resolution proxy data, revealing a strong coupling with Holocene rapid climate changes. The centennial‐scale Moulouya palaeohydrological history will be discussed with palaeoenvironmental data from the same record (palaeomagnetics, sedimentary charcoal record, anthracological analyses, snail analyses) to generate new ideas about the mid to late Holocene hydrological cycle in the southwestern Mediterranean. The deduced features of pronounced Lower Moulouya flooding and the decreased fire recurrence during Holocene cooling remain somewhat inconsistent with the interpretation of other palaeohydrological and paleaoecological records from the southwestern Mediterranean. However, enhanced Lower Moulouya flood frequencies between 3.2 and 2.7 cal. ka BP agree with increased floodplain aggradation in other major river systems of Mediterranean North Africa. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
39.
为提高矿区开采沉陷变形监测GPS-RTK快速定位的精度,通过对GPS-RTK基准站位置的选取和转换参数选择的实验,研究在使用GPS-RTK进行测量的过程中,提高在矿区开采沉陷变形监测中GPS-RTK快速定位测量的数据精度,并用实例与E级GPS网获取的静态定位数据进行对比,实验证明可以达到一级导线的精度要求。  相似文献   
40.
On the basis of NCEP/NCAR reanalysis data and yearbooks of CMA tropical cyclones, statistical analysis is performed for 1949—2013 offshore typhoons subjected to rapid decay(RD). This analysis indicates that RD typhoons are small-probability events, making up about 2.2% of the total offshore typhoons during this period. The RD events experience a decadal variation, mostly in the 1960 s and 1970 s(maximal in the 1970 s), rapidly decrease in the 1980 s and 1990 s and quickly increase from 2000. Also, RD typhoons show remarkable seasonal differences: they arise mainly in April and July-December, with the prime stage being in October-November. The offshore RD typhoons occur mostly in the South China Sea(SCS) and to a lesser extent in the East China Sea(ECS); however, none are observed over the Huang Sea and Bo Sea.Composite analysis and dynamic diagnosis of the RD typhoon-related large-scale circulations are performed.Physical quantities of the composite analysis consist of 500-h Pa height and temperature fields, vapor transfer, vertical wind shear(VWS), density of core convection(DCC), and high-level jet and upper-air outflow of the typhoon. The results suggest that(1) at the 500-h Pa height field, the typhoon is ahead of a westerly trough and under the effects of its passing trough;(2) at the temperature field, the typhoon is ahead of a temperature trough, with an invading cold tongue present;(3) at the vapor transfer field, water transfer into the RD typhoon is cut off; and(4) at higher levels, the related jet weakens and the outbreak of convection becomes attenuated in the typhoon core. In addition, VWS bears a relation to the RD typhoon; in particular, strong VWS favors RD occurrence.The differences in RD events between the SCS and ECS show that for the RD, the VWS of the ECS environmental winds is markedly stronger in comparison with its SCS counterpart. The cold advection invading into the typhoons is more intense in the SCS than in the ECS, and the low-level vapor transfer and high-level outflow are weaker in the SCS RD typhoons.Data analysis shows that sea surface temperature(SST), VWS, and DCC can be employed as efficient factors to predict RD occurrence. With appropriate SST, VWS, and DCC, a warning of RD occurrence can be given 36, 30-36,and 30 h, respectively, in advance. These values suggest that atmospheric SST responses lag. Owing to this time lag,the prediction of RD typhoons is possible.  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