全文获取类型
收费全文 | 726篇 |
免费 | 34篇 |
国内免费 | 29篇 |
专业分类
测绘学 | 284篇 |
大气科学 | 13篇 |
地球物理 | 67篇 |
地质学 | 117篇 |
海洋学 | 34篇 |
天文学 | 16篇 |
综合类 | 50篇 |
自然地理 | 208篇 |
出版年
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 22篇 |
2020年 | 17篇 |
2019年 | 27篇 |
2018年 | 23篇 |
2017年 | 35篇 |
2016年 | 40篇 |
2015年 | 35篇 |
2014年 | 35篇 |
2013年 | 111篇 |
2012年 | 44篇 |
2011年 | 39篇 |
2010年 | 32篇 |
2009年 | 21篇 |
2008年 | 19篇 |
2007年 | 30篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 15篇 |
2003年 | 20篇 |
2002年 | 18篇 |
2001年 | 20篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有789条查询结果,搜索用时 875 毫秒
211.
Deformation mechanism maps for feldspar rocks 总被引:6,自引:0,他引:6
Deformation mechanism maps for feldspar rocks were constructed based on recently published constitutive laws for dislocation and grain boundary diffusion creep of wet and dry plagioclase aggregates. The maps display constant temperature contours in stress-grain size space for strain rates ranging from 10−16 to 10−12 s−1.Two fields of dominance of grain boundary diffusion-controlled creep and dislocation creep are separated by a strongly grain size-sensitive transition zone. For wet rocks, diffusion-controlled creep dominates below a grain size of about 0.1–1 mm, depending on temperature, stress, strain rate and feldspar composition. Plagioclase aggregates containing up to 0.3 wt.% water as often found in natural feldspars are more than 2 orders of magnitude weaker than dry rocks. The strength of water-bearing feldspar rocks is moderately dependent on composition and water fugacity.For a grain size range of about 10–50 μm commonly observed in natural ultramylonites, the deformation maps predict that diffusion-controlled creep is dominant at greenschist to granulite facies conditions. Low viscosity estimates of 1018–1019 Pa·s from modeling postseismic stress relaxation and channel flow of the continental lower crust can only be reconciled with laboratory experiments assuming dislocation creep at high temperatures >900 °C or, at lower temperatures, diffusion creep of fine-grained rocks possibly localized in abundant high strain shear zones. For similar thermodynamic conditions and grain size, lower crustal rocks are predicted to be less than order of magnitude weaker than upper mantle rocks. 相似文献
212.
Valiya M. Hamza Fernando J.S. Silva Dias 《Physics of the Earth and Planetary Interiors》2005,152(4):223-256
A summary of heat flow data acquired over recent years in several areas in the eastern (Brazil and Paraguay) and western (Bolivia, Chile, Colombia and Ecuador) parts of South American continent are presented. The improvements in the database have allowed numerical representations of heat flow for southeastern and central segments of the Precambrian fold belts in Brazil, Central Andean cordilleras in Chile and Bolivia, Southern Volcanic arc in Peru, Neuquén Province in southwestern Argentina, Chaco basin in Paraguay, Oriente basin in Ecuador and the system of pericratonic basins in north central Colombia. The maps reveal considerable variability in heat flow, not only between the main tectonic units but also within them. The intra-regional variations seem to originate mainly from complexities in local geologic structures while the inter-regional ones seem to point to action of deep-seated tectonic processes. The cordilleran regions are, in general, characterized by relatively high heat flow (>70 mW/m2), compared with the coastal regions to the west and the Pre-cordilleran basins to the east. In the eastern part of the continent, heat flow is low to normal (<60 mW/m2), the exceptions being the Mesozoic rift basins, areas of Cenozoic alkaline intrusions and some isolated belts of overthrust tectonics in the central parts of Brazil. There are indications that heat flow is high in the Patagonian Platform relative to that found in the Brazilian Platform.In addition, polynomial methods were employed for examining large-scale variations of heat flow over the continent. Specifically, a general-purpose least square solution was used to determine the coefficients of up to fourth order in latitude and longitude. Some of the large-scale trends seen in low order polynomial representations seem to be indicative of the nature of deep-seated heat transfer processes. The systematic increase in regional heat flow in the north-south direction is an example. It is considered as the consequence of thermal blanketing effect of the continental segment of the South American lithosphere. Trends seen in higher order polynomials seem to be associated with regional tectonic patterns and subduction-related magmatism. Prominent among these are east-west trending belts of low heat flow in northern Peru and in central Chile, as well as the high heat flow belts in northern Chile, Altiplano of Bolivia and northwestern Argentina. Limitations arising from low data density and uneven geographic distribution warrant higher degree polynomial representations. 相似文献
213.
网络环境下分区统计地图制图子系统的设计与实现 总被引:1,自引:0,他引:1
分析了网络环境下分区统计地图表达信息的特点,根据其可视化地理统计信息的需要,运用Java Ap-plet技术,设计和开发了网络环境下交互式分区统计地图制图子系统。 相似文献
214.
1 IntroductionMapgeneralizationisoneoftheclassicalcartographicprob lems.Allmaps,aregeneralizedrepresentationsofthereality.Generalizationisnecessarytoimprovethedisplayqualityofsmallscalemaps,allowanalysiswithdifferentgradesofdetail;andreducedatastoragere… 相似文献
215.
闫浩文 《武汉大学学报(信息科学版)》1997,(1)
统计符号库的设计与实现是符号库软件的难点,一直没有得到较好的解决,制约着统计地图制图软件的开发和实用化。本文首先分析了符号绘制的常用方法及其应用于统计符号库设计的局限性,进而基于OO方法提出了统计符号库设计的一种新方案,并就该方案的几个难点给出了解决办法 相似文献
216.
地图拓扑数据的自动组织 总被引:1,自引:0,他引:1
李霖 《武汉大学学报(信息科学版)》1987,(4)
本文对地图上四种类型的拓扑关系——关联关系、邻接关系、重叠关系和同域关系及它们之间的相互关系作了简要说明,阐述了这四种类型拓扑关系的可计算性问题,即利用地图上的地理坐标数据可计算出拓扑关系数据,并简述了计算方法及过程。 相似文献
217.
Eid Al-Tarazi 《Natural Hazards》1994,10(1-2):79-96
The earthquake hazard in Jordan and its vicinity is assessed on the basis of probabilistic methods. For this purpose, an updated earthquake catalog is compiled which covers the period between AD 1–1989. The earthquakes lie between latitudes 27.0°-35.5° N and longitudes 32.0°-39.0° E. Thirteen seismic zones are defined on a regional seismic and tectonic map presented for the area. Point-source and line-source models are used. The seismic hazard parameters, namely, theb-parameter (of the Gutenberg-Richter relation),m
1 (the upper bound magnitude), and 4 (the annual rate of occurrence of earthquakes with local magnitudeM
L
4.0) are calculated for each zone. The results of the seismic hazard assessment are displayed as iso-acceleration contours expected to be exceeded during typical economic life times of structures, i.e. 50 and 100 years. For each model, two seismic hazard maps are derived. In order to determine the importance of the South-eastern Mediterranean zone and the north part of the Red Sea zone from a seismic hazard point of view for Jordan, one seismic hazard map which corresponds to 50 years' economic life for every model, excluding the seismicity of these zones, is derived. 相似文献
218.
A MODEL FOR QUANTITATIVELY ESTIMATING SHORT-RANGE PRECIPITATION BASED ON GMS DIGITALIZED CLOUD MAPS—PART Ⅱ:ASSESSMENT OF RESULTS FROM THE MODEL FOR SATELLITE-IMAGE QUANTITATIVELY ESTIMATING PRECIPITATION 下载免费PDF全文
This is Part Ⅱ of this series.It introduces the technique for recognizing MαCS phased properties and its precipitation center or centers by means of dynamic digitalized cloud maps and presents the assessment of the effectiveness of the model proposed in Part Ⅰ as to its fitting and forecasting accuracy. 相似文献
219.
桐柏—信阳一带区域地球化学调查是全国区域化探扫面的一部分。编图中涉及19和20投影带及4个1∶20万图幅的拼接,制图中存在不少技术难题。为了避免2个投影带产生的裂隙坐标不统一,将20带数据转换到19带,然后在高斯—克吕格座标表中查取座标自然值,并计算座标通用值后进行座标展绘,取得了较好的制图效果。 相似文献
220.
This study provides a procedure for assessing seismic hazardand uncertainties in regions that are characterised by a large non-instrumental earthquakedatabase and a seismic and tectonic behaviour which doesn't allow an evident seismic zonation.This procedure is a synthesis of the non-zoning or non-parametric methodology (using extremevalues distribution functions as proposed by Epstein and Lomnitz, 1966) and the zoning orparametric methodology (using the theorem of total probability as proposed by Cornell, 1968)via a logic tree procedure taking into consideration the advantages offered by each of these.Taking the area which we shall describe as the east coast of Spain and surrounding inland areas,an application was made and a specific logic tree was developed in order to solve the problems anduncertainties related to the evaluation of the seismic hazard using both methodologies. The use of thelogic tree allowed the systematisation of a large number of solutions obtained. A number of relevantresults were obtained which show that in some cases there are great differences in the seismichazard results provided by the non-zoning and the zoning methodologies. In these cases, mean value andstandard deviation of the obtained results provide an intermediate solution to the over-conservativeestimation provided by the non-zoning methodology and the lowest results provided by the zoningmethodology. In other cases results provided by both methodologies are significantly closer.In any case, synthesis among both methodologies gives a wider knowledge of the uncertaintiesassociated with the seismic hazard results. Finally uncertainties increase with the decreaseof the annual probability of exceedence and in sites with a seismic history of large size earthquakes. 相似文献