全文获取类型
收费全文 | 699篇 |
免费 | 45篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 314篇 |
大气科学 | 20篇 |
地球物理 | 120篇 |
地质学 | 91篇 |
海洋学 | 41篇 |
天文学 | 102篇 |
综合类 | 33篇 |
自然地理 | 43篇 |
出版年
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 4篇 |
2017年 | 13篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 35篇 |
2013年 | 30篇 |
2012年 | 18篇 |
2011年 | 47篇 |
2010年 | 23篇 |
2009年 | 41篇 |
2008年 | 48篇 |
2007年 | 40篇 |
2006年 | 36篇 |
2005年 | 36篇 |
2004年 | 23篇 |
2003年 | 35篇 |
2002年 | 14篇 |
2001年 | 19篇 |
2000年 | 23篇 |
1999年 | 25篇 |
1998年 | 23篇 |
1997年 | 29篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 27篇 |
1992年 | 18篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有764条查询结果,搜索用时 687 毫秒
591.
任何对地观测系统获得的原始图像数据实质上都是地球表面电磁波谱特征的综合反映。经地面站系统处 理得到的常规图像产品仍存在大气、地形等多种随机因素导致的几何畸变与辐射失真 , 并且多种地物目标信息混 杂 , 甚至相互迭掩 , 彼此抑制。所以 , 严格地说 , 这些图像只是一种信息源 , 属“数据”范畴 , 必须对其进行再 处理才能得到适应不同专业需要的优质图像和有用信息。至今 , 从事遥感图像处理的科技人员大多出身于电子、计 算机等专业 , 故对于不同地理景观、不同季节、不同传感器所获得的图像数据 (一串灰度数码) , 往往很难体会到 其中包含着的极为丰富而复杂的生物、地学内容。一个能出色完成一般图像处理任务的杰出图像处理专家 , 不一 定能胜任各种不同应用目的所要求的图像处理任务。常常使得海量遥感数据难以得到有效的利用。据此 , 笔者认 为应把遥感图像处理分解为系统处理与应用处理两大类 , 它们是既相互衔接又彼此有别的技术分支。前者只从图 像总体要求出发 , 着眼于改善、提高图像整体质量 ; 后者则必须密切关注具体的应用目的与对象 , 形成融入了地 学分析思路、并精确反映遥感成像机理的图像应用处理技术。文中给出了发展遥感图像应用处理技术的流程框图 , 列举了森林火灾、虫灾监测 , 洪涝灾情快速反应 , 城市扩展 , 低产土壤清查 , 土地利用动态监测等多项任务中的 成功实践。 相似文献
592.
593.
根据多年平均流场和卫星云图分析,提出了一种夏季北太平洋上中国至北症状,中美洲远洋船舶安全航行的航线选择区,它位于200hPa副热带高压脊线附近至其南部对流层上部槽以北广阔地区,并以实例作了较充分讨论。 相似文献
594.
Giovanni Guglielmo 《Geological Journal》1993,28(2):149-157
Contacts within nested plutons are crucial for constraining the relative timing of pluton emplacement and the internal geometry of composite plutons. Exposures in orogenic belts are commonly discontinuous, however, disguising these contacts. In this paper, the Merrimac plutons in the northern Sierra Nevada of California are used as an example of how composition and foliation patterns can allow the definition of unexposed contacts and identify nested plutons. Image analysis techniques were used to determine modal compositions of a total of 52 samples from the Merrimac plutons. The integrated analysis of compositional data and foliations patterns reveals a critical contact within the plutons, and suggests that the Merrimac plutons indicate way-up towards the north-east at the time of emplacement 142 ± 3 Ma ago. This paper provides guidelines for recognizing nested plutons in poorly exposed areas and shows that consistent structural and compositional assymmetries within nested plutons can be used as regional top-direction indicators. 相似文献
595.
596.
陆地卫星TM图像含有丰富的光谱信息,SPOT全色波段图像数据分辨率较高,因此,如何将这两种图像数据有效地结合起来,在遥感应用领域中显得越来越重要。本文研究了SPOT和TM图像数据的数字复合方法。结果表明,复合后的图像提高了分辨率,增加了光谱信息。 相似文献
597.
Seismic tomography is a well‐established approach to invert smooth macro‐velocity models from kinematic parameters, such as traveltimes and their derivatives, which can be directly estimated from data. Tomographic methods differ more with respect to data domains than in the specifications of inverse‐problem solving schemes. Typical examples are stereotomography, which is applied to prestack data and Normal‐Incidence‐Point‐wave tomography, which is applied to common midpoint stacked data. One of the main challenges within the tomographic approach is the reliable estimation of the kinematic attributes from the data that are used in the inversion process. Estimations in the prestack domain (weak and noisy signals), as well as in the post‐stack domain (occurrence of triplications and diffractions leading to numerous conflicting dip situations) may lead to parameter inaccuracies that will adversely impact the resulting velocity models. To overcome the above limitations, a new tomographic procedure applied in the time‐migrated domain is proposed. We call this method Image‐Incident‐Point‐wave tomography. The new scheme can be seen as an alternative to Normal‐Incidence‐Point‐wave tomography. The latter method is based on traveltime attributes associated with normal rays, whereas the Image‐Incidence‐Point‐wave technique is based on the corresponding quantities for the image rays. Compared to Normal‐Incidence‐Point‐wave tomography the proposed method eases the selection of the tomography attributes, which is shown by synthetic and field data examples. Moreover, the method provides a direct way to convert time‐migration velocities into depth‐migration velocities without the need of any Dix‐style inversion. 相似文献
598.
基于SIFT特征的SAR图像配准方法在玉树地震中的应用 总被引:1,自引:0,他引:1
本文针对SAR图像特点, 提出了基于改进SIFT(尺度不变特征变换)算法的SAR图像配准方案: ① 对待配准图像进行ISEF(无限对称指数滤波器)滤波处理, 降低图像的斑点噪声; ② 采用SIFT算法提取特征点, 略过差分金字塔第一层的特征点检测, 提高时间效率; ③ 在欧氏空间内剔除误匹配点, 提高配准精度。 实验表明, 本文提出的SAR图像配准方案检测到的匹配点对的数量和稳健性都有提高, 精度能够满足亚像元级SAR图像的应用需求, 且用时比传统SIFT方法减少60%以上。 最后对精配准的SAR图像进行震害变化检测, 得到的震害分布与高分辨率光学图像上判读的建筑物毁坏情况基本一致。 相似文献
599.
600.
Irrespective of their spatial extent, free-surface shallow flows are challenging measurement environments for most instruments due to the relatively small depths and velocities typically associated with these flows. A promising candidate for enabling measurements in such conditions is Large-scale Particle Image Velocimetry (LSPIV). This technique uses a non-intrusive approach to measure two-dimensional surface velocity fields with high spatial and temporal resolutions. Although there are many publications documenting the successful use of LSPIV in various laboratory and field open-channel flow situations, its performance has not been equally substantiated for measurement in shallow flows. This paper aims at filling in this gap by demonstrating the capabilities of LSPIV to: (a) accurately evaluate complex flow patterns in shallow channel flows; and (b) estimate depth in shallow flows using exclusively LSPIV measurements. The demonstration is provided by LSPIV measurements in three shallow flow laboratory situations with flow depths ranging from 0.05 to 0.31 m. The obtained measurements illustrate the LSPIV flexibility and reliability in measuring velocities in shallow and low-velocity (near-zero) flows. Moreover, the technique is capable to evaluate and map velocity-derived quantities that are difficult to document with alternative measurement techniques (e.g. vorticity and shear stress distributions and mapping of large-scale structure in the body of water). 相似文献