全文获取类型
收费全文 | 620篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 26篇 |
地球物理 | 115篇 |
地质学 | 246篇 |
海洋学 | 41篇 |
天文学 | 153篇 |
综合类 | 2篇 |
自然地理 | 47篇 |
出版年
2021年 | 8篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 12篇 |
2013年 | 30篇 |
2012年 | 18篇 |
2011年 | 19篇 |
2010年 | 27篇 |
2009年 | 16篇 |
2008年 | 23篇 |
2007年 | 28篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 24篇 |
2003年 | 18篇 |
2002年 | 22篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1997年 | 5篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 15篇 |
1974年 | 13篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1970年 | 4篇 |
1967年 | 4篇 |
1890年 | 3篇 |
排序方式: 共有637条查询结果,搜索用时 62 毫秒
111.
Lee?FawcettEmail author Amy?C.?Green 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(8):2233-2252
A key aim of most extreme value analyses is the estimation of the r-year return level; the wind speed, or sea-surge, or rainfall level (for example), we might expect to see once (on average) every r years. There are compelling arguments for working within the Bayesian setting here, not least the natural extension to prediction via the posterior predictive distribution. Indeed, for practitioners the posterior predictive return level has been cited as perhaps the most useful point summary from a Bayesian analysis of extremes, and yet little is known of the properties of this statistic. In this paper, we attempt to assess the performance of predictive return levels relative to their estimative counterparts obtained directly from the return level posterior distribution; in particular, we make comparisons with the return level posterior mean, mode and 95% credible upper bound. Differences between the predictive return level and standard summaries from the return level posterior distribution, for wind speed extremes observed in the UK, motivates this work. A large scale simulation study then reveals the superiority of the predictive return level over the other posterior summaries in many cases of practical interest. 相似文献
112.
The Goldstone radar system was used at a wavelength of 12.6 cm to probe the Martian surface during the 1973 opposition. Measurements of range and reflected power were made at least weekly between July 12 and November 24. Surface cells isolated by the radar system were 8 km E-W × 110 km N-S. Altitudes were calculated from signal time delays measured relative to a triaxial ellipsoid and were combined with altitudes measured during the 1971 opposition. Contours of constant altitude were calculated at 200 m intervals between latitudes ?14° and ?22°. These contours are presented in conjunction with Mars charts derived from Mariner 9 television pictures. Reflected power was measured at angles of incidence between ?5° and +5°. These measurements were combined with those obtained during the 1971 opposition. Predictions of the reflected power versus the angle of incidence were calculated from the exponential surface model of Hagfors. The predictions were fit to the data in a least-squares sense, using a nonlinear iterative procedure, to yield estimates of surface roughness and reflectivity. The smoother regions exhibit a typical reflectivity of 8.2%. A tendency for the reflectivity to decrease with increasing roughness was observed. 相似文献
113.
Liu Hongyan Jiang Zihan Dai Jingxi Wu Xiuchen Peng Jian Wang Hongya Meersmans Jeroen Green Sophie M. Quine Timothy A. 《中国科学:地球科学(英文版)》2019,62(11):1756-1763
The study of the critical zones(CZs) of the Earth link the composition and function of aboveground vegetation with the characteristics of the rock layers, providing a new way to study how the unique rock and soil conditions in karst regions affect the aboveground vegetation. Based on survey results of the rocks, soils and vegetation in the dolomite and limestone distribution areas in the karst area of central Guizhou, it was found that woody plant cover increases linearly with the number of cracks with a width of more than 1 mm, while the cover of herbaceous plants shows the opposite trend(p0.01). The dolomite distribution area is characterized by undeveloped crevices, and the thickness of the soil layer is generally less than 20 cm, which is suitable for the distribution of herbaceous plants with shallow roots. Due to the development of crevices in the limestone distribution area, the soil is deeply distributed through the crevices for the deep roots of trees, which leads to a diversified species composition and a complicated structure in the aboveground vegetation. Based on moderate resolution imaging spectroradiometer(MODIS) remote sensing data from 2001 to 2010, the normalized differentiated vegetation index(NDVI) and annual net primary productivity(NPP) results for each phase of a 16-day interval further indicate that the NDVI of the limestone distribution area is significantly higher than that in the dolomite distribution area, but the average annual NPP is the opposite. The results of this paper indicate that in karst CZs, the lithology determines the structure and distribution of the soil, which further determines the cover of woody and herbaceous plants in the aboveground vegetation. Although the amount of soil in the limestone area may be less than that in the dolomite area, the developed crevice structure is more suitable for the growth of trees with deep roots, and the vegetation activity is strong. At present, the treatment of rocky desertification in karst regions needs to fully consider the rock-soilvegetation-air interactions in karst CZs and propose vegetation restoration measures suitable for different lithologies. 相似文献
114.
We demonstrate that conventional palaeoseismic trenching and mapping techniques that do not account for the effects of off‐fault deformation can significantly underestimate a fault’s slip rate. Using combined interpretations of 3‐D ground‐penetrating radar (GPR) and palaeoseismic trench data, we show that drag folding and hangingwall and footwall horizontal‐axis rotations have accommodated up to 41% of total extension across a normal fault within the Taupo Rift, New Zealand, over the past 24.6 ± 1.0 cal. ka BP. Our results may explain why geologically determined fault‐slip rates for the central and southern Taupo Rift are anomalously low when compared with geodetic estimates. We suggest that a combination of GPR surveying and palaeoseismic trenching may help resolve differences between geodetically and geologically determined strain rates observed across active extensional regimes worldwide. 相似文献
115.
An established numerical tidal model has been used to investigate the impact of various sea-level rise (SLR) scenarios, as well as SLR in combination with large-scale tidal power plants on European shelf tidal dynamics. Even moderate and realistic levels of future SLR are shown to have significant impacts on the tidal dynamics of the area. These changes are further enhanced when SLR and tidal power plants are considered in combination, resulting in changes to tidal amplitudes, currents and associated tidal dissipation and bed shear stresses. Sea-level rise is the dominant influence on any far-field impacts, whereas tidal power plants are shown to have the prevailing influence over any changes close to the point of energy extraction. The spatial extent of the impacts of energy extraction is shown to be affected by the sea level when more than one tidal power plant in the Irish Sea was considered. Different ways to implement SLR in the model are also discussed and shown to be of great significance for the response of the tides. 相似文献
116.
117.
118.
In this paper we apply 3D inversion to MT data collected in the Northwestern United States as a part of the EarthScope project.
By the end of 2009 MT data had been collected from 262 stations located throughout Oregon, Washington, Idaho, and most of
Montana and Wyoming. We used data from 139 MT stations in this analysis. We developed fully parallelized rigorous 3D MT inversion
software based on the integral equation method with variable background conductivity. We also implemented a receiver footprint
approach which considerably reduced the computational resources needed to invert the large volumes of data covering vast areas.
The data set used in the inversion was obtained through the Incorporated Research Institutions for Seismology (IRIS). The
inversion domain was divided into 2.7 M cells. The inverted electrical conductivity distribution agrees reasonably well with
geological features of the region. 相似文献
119.
Anne E. Green 《The Professional geographer》2013,65(1):46-58
The Organization for Economic Co-operation and Development (OECD) has identified population aging as one of the most important challenges facing OECD countries and has highlighted the need for people to work longer and for job prospects for older workers to be enhanced. This article provides a summary review of a recent OECD report, Ageing and Employment Policies—Live Longer, Work Longer, as a platform to highlight differences between countries in demographic profiles and projections and in patterns of formal labor market participation among older workers. Drawing on selected information from a broader evidence base, it unveils important differences between countries in the scale of demographic and associated labor market challenges. It also explores factors affecting labor market transitions among older workers and age-related and other barriers to paid work among older people, emphasizing the diversity of experience between individuals. Finally, it highlights some strategic challenges for policy. 相似文献
120.
Paul F. Green Rob Westaway D.A.C. Manning Paul L. Younger 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(3):450-463
The Cenozoic landscape development of Britain remains relatively poorly understood. On the one hand, ‘plumists’ have tried to explain the present-day topography as a consequence of effects of the Iceland mantle plume during the Palaeocene-Eocene British Tertiary Igneous Province (BTIP) magmatism, with little or no subsequent modification. On the other hand, abundant evidence exists from fluvial and marine terraces and superimposed karstic levels for significant vertical crustal motions during the Quaternary, which clearly has nothing to do with any mantle plume. To shed light on this issue, we present the first publication of data that constrain the Cenozoic thermal history of the North Pennine uplands of northern England, from apatite fission-track analysis of drill cuttings from the Eastgate Borehole in Weardale, in the western part of County Durham. Our results indicate ~650 m of regional denudation since the latest Oligocene/Early Miocene, plus the ~400 m of localized entrenchment that has created the modern Weardale valley. Before the latest Oligocene/Early Miocene, but following the BTIP magmatism, the crust in this region experienced significant cooling, mainly due to a decrease in the geothermal gradient from ~55 to 61 °C km?1 to the present 38 °C km?1, along with ~300 ± 200 m of denudation. Although significant BTIP magmatism occurred in northern England, it thus had only a limited net effect; the crust experienced dramatic heating, but cooled back to its original thermal state within, at most, a few tens of millions of years. We suggest that this rapid cooling effect resulted from westward flow of relatively cold material within the mobile lower-crustal layer, driven by the lateral pressure gradient induced by earlier heating effects and effects of surface processes. Whatever topography developed during the Palaeogene, as a direct result of these heating effects, underplating at the base of the crust, and the associated modest denudation, was presumably also short-lived; significant changes to the crustal thickness, and thus to the topography, can be envisaged as a consequence of subsequent lower-crustal flow. 相似文献