全文获取类型
收费全文 | 8342篇 |
免费 | 840篇 |
国内免费 | 845篇 |
专业分类
测绘学 | 3695篇 |
大气科学 | 717篇 |
地球物理 | 894篇 |
地质学 | 1748篇 |
海洋学 | 873篇 |
天文学 | 45篇 |
综合类 | 763篇 |
自然地理 | 1292篇 |
出版年
2024年 | 9篇 |
2023年 | 66篇 |
2022年 | 357篇 |
2021年 | 399篇 |
2020年 | 411篇 |
2019年 | 343篇 |
2018年 | 287篇 |
2017年 | 424篇 |
2016年 | 407篇 |
2015年 | 440篇 |
2014年 | 428篇 |
2013年 | 597篇 |
2012年 | 469篇 |
2011年 | 478篇 |
2010年 | 381篇 |
2009年 | 464篇 |
2008年 | 487篇 |
2007年 | 513篇 |
2006年 | 424篇 |
2005年 | 409篇 |
2004年 | 375篇 |
2003年 | 316篇 |
2002年 | 265篇 |
2001年 | 223篇 |
2000年 | 179篇 |
1999年 | 140篇 |
1998年 | 165篇 |
1997年 | 147篇 |
1996年 | 95篇 |
1995年 | 59篇 |
1994年 | 51篇 |
1993年 | 44篇 |
1992年 | 54篇 |
1991年 | 34篇 |
1990年 | 22篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
1993~2003年厦门市湿地动态变化及其驱动因素分析 总被引:1,自引:3,他引:1
通过对厦门市1993年TM遥感影像和2003年ETM 遥感影像的解译分析和数据统计,从湿地面积动态变化和湿地消长情况等方面,用单一土地利用动态度等指标对1993~2003年期间厦门市的湿地变化进行了研究。结果表明,1993~2003年期间厦门市天然湿地面积减少了2103hm2,其中有954hm2(滩涂864hm2)转变为非湿地,有1149hm2转变为人工湿地;而人工湿地面积增加了2775hm2,其中养殖场面积从1993年的5778hm2迅猛增加到2003年的9768hm2,年均增长率为6.91%,水库与水塘和盐田则分别减少了961hm2和254hm2。有27.74%、11.41%、9.33%和3.63%的养殖场面积分别是由非湿地、滩涂、盐田和水库与水塘转变而来的;有54.37%的盐田转变成了养殖场,有33.24%、30.24%的红树林转变为非湿地、养殖场,有10.35%、8.64%的滩涂转变为养殖场、非湿地。对社会经济驱动因素的分析表明,经济发展、人口增长和农业生产比较利益因素极大影响着厦门市湿地的动态变化。 相似文献
142.
Faisal Hossain 《Natural Hazards》2006,37(3):263-276
The three most important components necessary for functioning of an operational flood warning system are: (1) a rainfall measuring
system; (2) a soil moisture updating system; and, (3) a surface discharge measuring system. Although surface based networks
for these systems can be largely inadequate in many parts of the world, this inadequacy particularly affects the tropics,
which are most vulnerable to flooding hazards. Furthermore, the tropical regions comprise developing countries lacking the
financial resources for such surface-based monitoring. The heritage of research conducted on evaluating the potential for
measuring discharge from space has now morphed into an agenda for a mission dedicated to space-based surface discharge measurements.
This mission juxtaposed with two other upcoming space-based missions: (1) for rainfall measurement (Global Precipitation Measurement,
GPM), and (2) soil moisture measurement (Hydrosphere State, HYDROS), bears promise for designing a fully space-borne system
for early warning of floods. Such a system, if operational, stands to offer tremendous socio-economic benefit to many flood-prone
developing nations of the tropical world. However, there are two competing aspects that need careful assessment to justify
the viability of such a system: (1) cost-effectiveness due to surface data scarcity; and (2) flood prediction uncertainty
due to uncertainty in the remote sensing measurements. This paper presents the flood hazard mitigation opportunities offered
by the assimilation of the three proposed space missions within the context of these two competing aspects. The discussion
is cast from the perspective of current understanding of the prediction uncertainties associated with space-based flood prediction.
A conceptual framework for a fully space-borne system for early-warning of floods is proposed. The need for retrospective
validation of such a system on historical data comprising floods and its associated socio-economic impact is stressed. This
proposal for a fully space-borne system, if pursued through wide interdisciplinary effort as recommended herein, promises
to enhance the utility of the three space missions more than what their individual agenda can be expected to offer. 相似文献
143.
Groundwater study using remote sensing and geographic information systems (GIS) in the central highlands of Eritrea 总被引:3,自引:1,他引:3
Remote sensing, evaluation of digital elevation models (DEM), geographic information systems (GIS) and fieldwork techniques were combined to study the groundwater conditions in Eritrea. Remote sensing data were interpreted to produce lithological and lineament maps. DEM was used for lineament and geomorphologic mapping. Field studies permitted the study of structures and correlated them with lineament interpretations. Hydrogeological setting of springs and wells were investigated in the field, from well logs and pumping test data. All thematic layers were integrated and analysed in a GIS. Results show that groundwater occurrence is controlled by lithology, structures and landforms. Highest yields occur in basaltic rocks and are due to primary and secondary porosities. High yielding wells and springs are often related to large lineaments, lineament intersections and corresponding structural features. In metamorphic and igneous intrusive rocks with rugged landforms, groundwater occurs mainly in drainage channels with valley fill deposits. Zones of very good groundwater potential are characteristic for basaltic layers overlying lateritized crystalline rocks, flat topography with dense lineaments and structurally controlled drainage channels with valley fill deposits. The overall results demonstrate that the use of remote sensing and GIS provide potentially powerful tools to study groundwater resources and design a suitable exploration plan.The online version of the original article can be found at 相似文献
144.
介绍光谱排序编码法的原理并对其进行精度验证:在14种矿物的56个样品中最高精度为100%,最低为57%,平均为79.4%;分别提取包尔图地区以方解石、Al-OH Mg-OH和石英为主的岩石分布状况,与该区地质图对比结果表明,其分布与实际情况大体相同,从而证实了光谱排序编码法的目标提取能力。 相似文献
145.
植被是东亚飞蝗发生和成灾的重要指示因子。运用遥感技术对植被生长进行监测,对东亚飞蝗的预测和防治具有重要意义。以河北省黄骅市为研究区,利用实地获取的植被冠层孔隙度数据反算的LAI数据以及Landsat-5 TM影像提取的各种VI数据,进行了LAI(LAI-2000改进型算法的反算结果)与TM影像上反演的VI之间的相关分析。结果表明,RDVI最适合反映研究区植被生长状况。分析RDVI与飞蝗发生面积的关系,发现两者呈负线性相关,即随着RDVI减小,飞蝗的发生面积呈线性增大。 相似文献
146.
长江口水域多光谱遥感水深反演模型研究 总被引:3,自引:0,他引:3
利用Landsat-7 ETM 遥感影像反射率和实测水深值之间的相关性可以探测水深。该文介绍单波段、双波段比值和多波段3种线性回归模型以及动量BP人工神经网络水深反演模型。选择长江口北港河道上段作为研究区,利用上述模型,分两种情况进行水深反演:一是以河道全部历史样本建模;二是将河道按自然水深划分为浅水区和深水区分别建模。结果表明:神经网络模型预测精度高于线性回归模型;水深分区后线性回归和神经网络模型预测误差均有所减小。 相似文献
147.
渤海湾北部滨外沙坝演变的遥感分析 总被引:1,自引:0,他引:1
通过多时相航空遥感影像和MSS、TM、ETM卫星遥感影像的解译、对比,分析渤海湾北部滨外沙坝近50年来的演变过程。结果表明:在波浪、潮汐、潮流和河流等动力因素的作用下,滨外沙坝的动态变化较为明显,在整体西向漂移、向海侧边线蚀退的背景下,个体沙坝的变化表现为陆向蚀退、侵蚀消亡、西南向漂移与端点蚀退、西向漂移与端点延展和海向淤进与陆向蚀退交替等多种态势。 相似文献
148.
全球及区域模式中陆面过程的地表植被覆盖分类方法 总被引:1,自引:0,他引:1
全球和区域尺度上陆面生态系统与气候密切相关。全球和区域模式的发展对于我们认识气候与陆地生态的变化起到重要作用。在这些模型中,植被覆盖是影响大气-植被间热量、水分和CO2等交换的重要陆面参数。在分析了陆地植被覆盖分类原理基础上,介绍了目前全球不同植被覆盖分类方案,包括基于地基观测的植被分布、基于生物气候特征的分类方案(如:Holdridge的方案);特别近年来陆面过程试验表明,各种遥感数据源(如:NOAA—AVHRR,EOS—MODIS,Landsat—TM)等为我们提供了有利的工具来监测全球植被动态,完善植被分类,并且采用高时空分辨率的全球土地覆盖状况特征,在不同时空尺度揭示植被-大气相互作用。本文分析了代表性的3种基于卫星遥感技术的陆面植被分类方案,分别是BATS(18类)、SIB(9类)、SIB2(12类)和BIOME—BGC(31类)陆地模式的植被覆盖分类方案.最后分析了目前可用于全球植被覆盖分类的新的遥感数据库。 相似文献
149.
遥感技术在黑竹沟风景旅游资源调查分类与评价中的应用 总被引:1,自引:1,他引:1
随着信息技术的发展,遥感成为了旅游资源调查评价的新手段。阐述了运用遥感新技术对四川省乐山市黑竹沟风景旅游区旅游资源进行调查的过程,并结合现场调研和相关资料对其旅游资源进行了分类和评价。首先对黑竹沟风景旅游区2003年的ETM影像数据遥感图像进行了处理,然后建立了解译标志进行旅游资源信息的提取和分析,最后对黑竹沟风景旅游区的旅游资源进行了客观全面的分类和评价。黑竹沟的旅游资源可分为2大类、7亚类、21个基本类型,是一处景源内容丰富、景象多变的旅游区,发展潜力巨大。 相似文献
150.
Driving forces of tropical deforestation: The role of remote sensing and spatial models 总被引:2,自引:0,他引:2
Rinku Roy Chowdhury 《Singapore journal of tropical geography》2006,27(1):82-101
Remote sensing technologies are increasingly used to monitor landscape change in many parts of the world. While the availability of extensive and timely imagery from various satellite sensors can aid in identifying the rates and patterns of deforestation, modelling techniques can evaluate the socioeconomic and biophysical forces driving deforestation processes. This paper briefly reviews some emerging spatial methodologies aimed at identifying driving forces of land use change and applies one such methodology to understand deforestation in Mexico. Satellite image classification, change analysis and econometric modelling are used to identify the rates, hotspots and drivers of deforestation in a case study of the southern Yucatán peninsular region, an enumerated global hotspot of biodiversity and tropical deforestation. In particular, the relative roles of biophysical and socioeconomic factors in driving regional deforestation rates are evaluated. Such methodological approaches can be applied to other regions of the forested tropics and contribute insights to conservation planning and policy. 相似文献