全文获取类型
收费全文 | 33765篇 |
免费 | 18212篇 |
国内免费 | 43305篇 |
专业分类
测绘学 | 3074篇 |
大气科学 | 21282篇 |
地球物理 | 12372篇 |
地质学 | 34902篇 |
海洋学 | 16261篇 |
天文学 | 718篇 |
综合类 | 4314篇 |
自然地理 | 2359篇 |
出版年
2024年 | 191篇 |
2023年 | 408篇 |
2022年 | 641篇 |
2021年 | 952篇 |
2020年 | 2058篇 |
2019年 | 5486篇 |
2018年 | 5618篇 |
2017年 | 5329篇 |
2016年 | 5368篇 |
2015年 | 4838篇 |
2014年 | 4259篇 |
2013年 | 4869篇 |
2012年 | 4631篇 |
2011年 | 4395篇 |
2010年 | 4383篇 |
2009年 | 3692篇 |
2008年 | 2977篇 |
2007年 | 3023篇 |
2006年 | 2681篇 |
2005年 | 2531篇 |
2004年 | 2813篇 |
2003年 | 2497篇 |
2002年 | 2234篇 |
2001年 | 2007篇 |
2000年 | 1607篇 |
1999年 | 1566篇 |
1998年 | 1658篇 |
1997年 | 1722篇 |
1996年 | 1329篇 |
1995年 | 1289篇 |
1994年 | 1158篇 |
1993年 | 1135篇 |
1992年 | 962篇 |
1991年 | 720篇 |
1990年 | 690篇 |
1989年 | 572篇 |
1988年 | 501篇 |
1987年 | 385篇 |
1986年 | 310篇 |
1985年 | 243篇 |
1984年 | 279篇 |
1983年 | 167篇 |
1982年 | 204篇 |
1981年 | 146篇 |
1980年 | 108篇 |
1979年 | 112篇 |
1978年 | 46篇 |
1977年 | 42篇 |
1971年 | 53篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
351.
针对传统矿化信息提取方法单一,利用光谱或纹理、信息量相对较少、需要大量样本的缺陷,利用基于光谱和纹理的支持向量机(SVM)原理,建立矿化信息提取模型.选择青海泽库县析界日地区作为典型研究区.首先提取研究区光谱和纹理信息,选取训练样本;然后求解最优超平面,进而确定决策函数;最后泛化推广识别其他待识别的样本.通过所提取的遥感蚀变异常信息与重砂异常点叠加分析,叠加基本吻合;从野外实地验证来看,均发现了不同程度的矿化现象,并指出了5个重点异常区. 相似文献
352.
Accuracy assessment of lidar-derived digital elevation models 总被引:2,自引:0,他引:2
Despite the relatively high cost of airborne lidar-derived digital elevation models (DEMs), such products are usually presented without a satisfactory associated estimate of accuracy. For the most part, DEM accuracy estimates are typically provided by comparing lidar heights against a finite sample of check point coordinates from an independent source of higher accuracy, supposing a normal distribution of the derived height differences or errors. This paper proposes a new methodology to assess the vertical accuracy of lidar DEMs using confidence intervals constructed from a finite sample of errors computed at check points. A non-parametric approach has been tested where no particular error distribution is assumed, making the proposed methodology especially applicable to non-normal error distributions of the type usually found in DEMs derived from lidar. The performance of the proposed model was experimentally validated using Monte Carlo simulation on 18 vertical error data-sets. Fifteen of these data-sets were computed from original lidar data provided by the International Society for Photogrammetry and Remote Sensing Working Group III/3, using their respective filtered reference data as ground truth. The three remaining data-sets were provided by the Natural Environment Research Council's Airborne Research and Survey Facility lidar system, together with check points acquired using high precision kinematic GPS. The results proved promising, the proposed models reproducing the statistical behaviour of vertical errors of lidar using a favourable number of check points, even in the cases of data-sets with non-normally distributed residuals. This research can therefore be considered as a potentially important step towards improving the quality control of lidar-derived DEMs. 相似文献
353.
湖子地区位于NNE向诸广-新兴铀成矿带与近EW向大东山-漳州大断裂复合部位,是华南早、晚两期铀成矿热液活动叠加区、放射性高场区,既有"硅化带大脉"型铀矿产出,又有"交点"型铀矿存在,找矿前景良好.文章在论述下庄矿田铀成矿地质环境、铀成矿特征及铀矿定位条件基础上,分析了湖子地区铀成矿条件与找矿前景,指出该区今后铀矿找矿方向是:① 6009号硅化断裂带,在其北段找硅化带大脉型铀矿,在其南段找"交点"型铀矿;②新桥-下庄硅化断裂带和6009号带之间成矿部位,寻找硅化带型和"交点"型铀矿;③NW向、近EW向辉绿岩脉与NNE向、NE向构造交汇部位(交点),寻找"交点"型铀矿. 相似文献
354.
Three-dimensional modelling from single images remains an interesting topic of investigation in the research community, even though range sensors are becoming a common alternative for the generation of 3D information. The interest in single-image-based modelling is motivated by a wide spectrum of applications such as cultural heritage, civil engineering, urban planning and even criminology. In this paper a complete new production flowline is presented for modelling based on a single image. The modelling process consists of a series of familiar steps in photogrammetry and computer vision: feature extraction, vanishing point computation, camera self-calibration, 3D reconstruction and dimensional analysis. In particular, the methodology developed for single-image-based modelling takes a scientific approach combining several proven techniques with robust estimators. Finally, in order to demonstrate its capabilities, the reported examples include several real situations applied in different contexts. 相似文献
355.
356.
357.
基于OFDM核心技术的WiMAX(全球微波接入互操作性)具有4G技术的特点。与3G和WiFi无线通讯技术相比具有明显的高速率、大容量数据传输优势。本文就基于WiMAX的地质灾害应急通讯系统的几种技术方案加以详细论述,说明WiMAX在地质灾害应急指挥中具有广阔前景。 相似文献
358.
359.
V. A. Simonov E. V. Sharkov S. V. Kovyazin N. S. Bortnikov 《Doklady Earth Sciences》2008,419(2):284-287
360.