全文获取类型
收费全文 | 7220篇 |
免费 | 889篇 |
国内免费 | 1018篇 |
专业分类
测绘学 | 1908篇 |
大气科学 | 804篇 |
地球物理 | 1532篇 |
地质学 | 2269篇 |
海洋学 | 802篇 |
天文学 | 584篇 |
综合类 | 505篇 |
自然地理 | 723篇 |
出版年
2024年 | 35篇 |
2023年 | 89篇 |
2022年 | 210篇 |
2021年 | 304篇 |
2020年 | 351篇 |
2019年 | 360篇 |
2018年 | 247篇 |
2017年 | 389篇 |
2016年 | 374篇 |
2015年 | 379篇 |
2014年 | 444篇 |
2013年 | 503篇 |
2012年 | 443篇 |
2011年 | 400篇 |
2010年 | 376篇 |
2009年 | 420篇 |
2008年 | 450篇 |
2007年 | 501篇 |
2006年 | 452篇 |
2005年 | 360篇 |
2004年 | 332篇 |
2003年 | 276篇 |
2002年 | 234篇 |
2001年 | 210篇 |
2000年 | 162篇 |
1999年 | 129篇 |
1998年 | 143篇 |
1997年 | 94篇 |
1996年 | 91篇 |
1995年 | 55篇 |
1994年 | 72篇 |
1993年 | 50篇 |
1992年 | 44篇 |
1991年 | 26篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 8篇 |
1987年 | 19篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 6篇 |
1976年 | 2篇 |
排序方式: 共有9127条查询结果,搜索用时 15 毫秒
951.
ZY-102C星数据在矿山遥感监测中的应用研究与分析 总被引:1,自引:0,他引:1
利用资源一号(ZY-1)02C卫星(以下简称02C星)全色高分辨率相机(HR)和多光谱相机(MUX)数据,以河北承德多金属矿区和江西寻乌稀土矿区为实验区,开展了1∶5万矿山遥感监测应用研究;分析了应用过程中存在的问题,提出了解决方案和建议,对02C星数据在矿山遥感监测中的规模化应用起到了示范效果。研究结果表明:在数据处理流程上,对空间分辨率为2.36 m的02C星全色HR1与HR2数据需先进行正射纠正再拼接,对空间分辨率为10 m的多光谱数据MUX可采用假彩色合成方法进行模拟真彩色合成;在矿山地物识别上,与SPOT5图像比较,02C星图像可更好地反映出开采面、开采点、中转场和矿山建筑等矿山地物类型,不足之处是纹理信息较平滑、矿山地物的边界相对模糊,因而增加了室内解译的难度;在经济效益上,02C星数据的性价比优势明显。因此,尽管02C星数据处理和解译工作量较大,但其能满足1∶5万矿山遥感监测要求,总体经济效益显著。 相似文献
952.
Nature,origin and evolution of a Late Pleistocene incised valley‐fill,Sunda Shelf,Southeast Asia
下载免费PDF全文
![点击此处可从《Sedimentology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Faisal A. Alqahtani Howard D. Johnson Christopher A.‐L. Jackson Mohd Rapi B. Som 《Sedimentology》2015,62(4):1198-1232
Understanding the stratigraphic fill and reconstructing the palaeo‐hydrology of incised valleys can help to constrain those factors that controlled their origin, evolution and regional significance. This condition is addressed through the analysis of a large (up to 18 km wide by 80 m deep) and exceptionally well‐imaged Late Pleistocene incised valley from the Sunda Shelf (South China Sea) based on shallow three‐dimensional seismic data from a large (11 500 km2), ‘merge’ survey, supplemented with site survey data (boreholes and seismic). This approach has enabled the characterization of the planform geometry, cross‐sectional area and internal stratigraphic architecture, which together allow reconstruction of the palaeo‐hydrology. The valley‐fill displays five notable stratigraphic features: (i) it is considerably larger than other seismically resolvable channel forms and can be traced for at least 180 km along its length; (ii) it is located in the axial part of the Malay Basin; (iii) the youngest part of the valley‐fill is dominated by a large (600 m wide and 23 m deep), high‐sinuosity channel, with well‐developed lateral accretion surfaces; (iv) the immediately adjacent interfluves contain much smaller, dendritic channel systems, which resemble tributaries that drained into the larger incised valley system; and (v) a ca 16 m thick, shell‐bearing, Holocene clay caps the valley‐fill. The dimension, basin location and palaeo‐hydrology of this incised valley leads to the conclusion that it represents the trunk river, which flowed along the length of the Malay Basin; it connected the Gulf of Thailand in the north with the South China Sea in the south‐east. The length of the river system (>1200 km long) enables examination of the upstream to downstream controls on the evolution of the incised valley, including sea‐level, climate and tectonics. The valley size, orientation and palaeo‐hydrology suggest close interaction between the regional tectonic framework, low‐angle shelf physiography and a humid‐tropical climatic setting. 相似文献
953.
《Comptes Rendus Geoscience》2015,347(3):112-123
Aside common methods as seismology, ground deformation, and geochemistry, electromagnetic and especially electric ones can efficiently be applied for imaging and monitoring active volcanoes and hydrothermal systems that most often control the initial eruptive phase. Surveys and mappings image ground fluids flow, faults systems, and structural interfaces with anomalies up to several hundred of mV. Reiteration of surveys highlights time and spatial evolution. Continuous networks must extend surveys when the activity becomes stronger. Resolution in the data can reach a few microvolts as compared to the tens of millivolts for surveys. Observations made on several volcanoes definitively show that electric signals, up to some tens of millivolts, may appear some hours to a few weeks before ground deformation and seismicity, and are related to some extent to the location of the future activity. These transient signals may have a relationship with those recorded aboard satellites. Both of them appear during the transition period between the “fatigue” and the “dynamical” stages, which announces accelerating and irreversible processes. 相似文献
954.
Undernutrition, obesity, climate change, and freshwater depletion share food and agricultural systems as an underlying driver. Efforts to more closely align dietary patterns with sustainability and health goals could be better informed with data covering the spectrum of countries characterized by over- and undernutrition. Here, we model the greenhouse gas (GHG) and water footprints of nine increasingly plant-forward diets, aligned with criteria for a healthy diet, specific to 140 countries. Results varied widely by country due to differences in: nutritional adjustments, baseline consumption patterns from which modeled diets were derived, import patterns, and the GHG- and water-intensities of foods by country of origin. Relative to exclusively plant-based (vegan) diets, diets comprised of plant foods with modest amounts of low-food chain animals (i.e., forage fish, bivalve mollusks, insects) had comparably small GHG and water footprints. In 95 percent of countries, diets that only included animal products for one meal per day were less GHG-intensive than lacto-ovo vegetarian diets (in which terrestrial and aquatic meats were eliminated entirely) in part due to the GHG-intensity of dairy foods. The relatively optimal choices among modeled diets otherwise varied across countries, in part due to contributions from deforestation (e.g., for feed production and grazing lands) and highly freshwater-intensive forms of aquaculture. Globally, modest plant-forward shifts (e.g., to low red meat diets) were offset by modeled increases in protein and caloric intake among undernourished populations, resulting in net increases in GHG and water footprints. These and other findings highlight the importance of trade, culture, and nutrition in diet footprint analyses. The country-specific results presented here could provide nutritionally-viable pathways for high-meat consuming countries as well as transitioning countries that might otherwise adopt the Western dietary pattern. 相似文献
955.
合成孔径雷达(Synthetic Aperture Radar,SAR)技术凭借其全天时、全天候的成像能力以及对森林垂直结构信息敏感的特点,在森林资源监测中具有独特的优势,已成为当前森林资源遥感调查技术的研究热点.本文首先介绍了SAR森林资源监测技术的发展背景、发展轨迹和相关知识;然后,重点阐述了极化SAR、干涉SAR、极化干涉SAR和层析SAR在林地覆盖类型分类、变化检测以及森林参数定量化估测应用中的技术方法;最后,就SAR在森林资源监测研究和应用中存在的问题与发展趋势进行了总结与展望. 相似文献
956.
为保障城市地下空间开发利用的安全性,促进城市可持续发展,通过文献调研、现场调查和专家咨询等方法,分析提出城市地下空间监测的五项原则,将监测对象划分为三类:工程结构本体、周围岩土体以及周边环境。将监测指标归纳为变形类、力学类、振动类和宏观状态类共四类,其中变形类指标执行双控要求,其他三种指标执行单控要求。监测趋势预测分析可采用公式法、回归分析法、时间序列分析法、灰色预测法、神经网络法和支持向量机法等。全国各地监测控制值基本一致,但预警分级标准存在地区差异,其中北京市和广州市分级预警具有较大参考价值。目前城市地下空间安全监测存在七项不足:预警分级标准不完善,人工监测效率低,监测参数单一,监测信息缺少共享协同,测量精度较低,重监测轻预测以及缺乏数据融合和机器学习应用。针对这些问题,可采取七项措施进行改进:建立合理预警分级标准,发展自动化与智能化监测,多参数综合监测,应用远程监测与云平台,开发高精度测量设备,监测和预测并重,以及数据融合与机器学习应用。 相似文献
957.
大理州潜在蒸散量的计算及应用 总被引:1,自引:0,他引:1
利用云南大理州12个气象站1961—2010年气温、日照、风速、蒸发量等观测资料,运用彭曼—蒙蒂斯公式计算大理州潜在蒸散量及湿润度指数,并对大理州潜在蒸散量的时空分布特征进行分析,对干旱情况进行评价。结果表明,大理州潜在蒸散量东部大,南部次之,北部最小。月潜在蒸散量5月最大,12月最小,1—5月递增,5—12月递减。1994—2010的平均潜在蒸散量明显大于1961—1993年。大理州潜在蒸散量与降水量、水汽压、气温、净辐射呈显著正相关关系,与风速没有明显的相关关系。正常年份大理州11月至次年5月都存在不同程度的干旱。 相似文献
958.
Urban green commons: Insights on urban common property systems 总被引:1,自引:0,他引:1
Johan Colding Stephan Barthel Pim Bendt Robbert Snep Wim van der Knaap Henrik Ernstson 《Global Environmental Change》2013,23(5):1039-1051
The aim of this paper is to shed new light on urban common property systems. We deal with urban commons in relation to urban green-space management, referring to them as urban green commons. Applying a property-rights analytic perspective, we synthesize information on urban green commons from three case-study regions in Sweden, Germany, and South Africa, and elaborate on their role for biodiversity conservation in urban settings, with a focus on business sites. Cases cover both formally established types of urban green commons and bottom-up emerged community-managed habitats. As our review demonstrates, the right to actively manage urban green space is a key characteristic of urban green commons whether ownership to land is in the private, public, the club realm domain, or constitutes a hybrid of these. We discuss the important linkages among urban common property systems, social–ecological learning, and management of ecosystem services and biodiversity. Several benefits can be associated with urban green commons, such as a reduction of costs for ecosystem management and as designs for reconnecting city-inhabitants to the biosphere. The emergence of urban green commons appears closely linked to dealing with societal crises and for reorganizing cities; hence, they play a key role in transforming cities toward more socially and ecologically benign environments. While a range of political questions circumscribe the feasibility of urban green commons, we discuss their usefulness in management of different types of urban habitats, their political justification and limitation, their potential for improved biodiversity conservation, and conditions for their emergence. We conclude by postulating some general policy advice. 相似文献
959.
960.
W. Aoki 《Astronomische Nachrichten》2014,335(1):27-31
The High Dispersion Spectrograph (HDS) is the échelle spectrograph for an open‐use instrument of the Subaru Telescope. The current status of the instrument is reviewed. The new image slicers that significantly improve the efficiency of observations with very high resolving power have been installed in the past three years. Brief overview of recent science results is given on studies of early generations of stars and extra‐solar planets. An upgrade plan and future prospects of this instrument are discussed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献