全文获取类型
收费全文 | 455篇 |
免费 | 8篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 69篇 |
地球物理 | 91篇 |
地质学 | 145篇 |
海洋学 | 56篇 |
天文学 | 24篇 |
综合类 | 3篇 |
自然地理 | 71篇 |
出版年
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 26篇 |
2012年 | 17篇 |
2011年 | 10篇 |
2010年 | 20篇 |
2009年 | 13篇 |
2008年 | 21篇 |
2007年 | 11篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 3篇 |
2000年 | 18篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有469条查询结果,搜索用时 31 毫秒
141.
142.
The World Summit on Sustainable Development (26 August–4 September 2002), held in Johannesburg on the tenth anniversary of the first Earth Summit, provides the opportunity to reflect on the meaning of the sustainable development concept. This paper uses the case study of the Russian Federation to explore the relationship between official interpretations of sustainable development and alternative understandings concerned with the betterment of humankind, which draw on Russia's cultural and scientific heritage. It is suggested that there is much to be gained from reopening the sustainable development debate to incorporate such cultural particularities, both at the national and international levels. 相似文献
143.
144.
Jincheng Jiang Qingquan Li Wei Tu Shih-Lung Shaw 《International journal of geographical information science》2019,33(3):618-644
Sampling fraction is crucial to sampling-related studies and applications, especially in the big data era when most data are neither originally designed nor controllable in the data collection process. A common concern among researchers is ‘what’s the modelling accuracy when using a sample?’. Taking intra-city human mobility as the study objective, this study utilizes a simple and direct method to analyse the influences of various sampling fractions on modelling accuracy. Five common intra-city human mobility indicators (travel distance, travel time, travel frequency, radius of gyration and movement entropy) are evaluated considering mean value, median and probability distribution. Experimental results demonstrate that the representativeness of each considered indicator converges to 1 in its own unique rate and variances. The minimum required sampling fractions to satisfy specific accuracies differ for various indicators and evaluation measures. To further investigate how related factors influence the modelling accuracy of sampling fractions, additional experiments are conducted considering multiple sampling methods, study scopes, and data sources. Several interesting general findings are observed. This study provides a reference for other sampling-based applications. 相似文献
145.
Matthew J. Westoby David R. Rounce Thomas E. Shaw Catriona L. Fyffe Peter L. Moore Rebecca L. Stewart Benjamin W. Brock 《地球表面变化过程与地形》2020,45(14):3431-3448
There exists a need to advance our understanding of debris-covered glacier surfaces over relatively short timescales due to rapid, climatically induced areal expansion of debris cover at the global scale, and the impact debris has on mass balance. We applied unpiloted aerial vehicle structure-from-motion (UAV-SfM) and digital elevation model (DEM) differencing with debris thickness and debris stability modelling to unravel the evolution of a 0.15 km2 region of the debris-covered Miage Glacier, Italy, between June 2015 and July 2018. DEM differencing revealed widespread surface lowering (mean 4.1 ± 1.0 m a-1; maximum 13.3 m a-1). We combined elevation change data with local meteorological data and a sub-debris melt model, and used these relationships to produce high resolution, spatially distributed maps of debris thickness. These maps were differenced to explore patterns and mechanisms of debris redistribution. Median debris thicknesses ranged from 0.12 to 0.17 m and were spatially variable. We observed localized debris thinning across ice cliff faces, except those which were decaying, where debris thickened. We observed pervasive debris thinning across larger, backwasting slopes, including those bordered by supraglacial streams, as well as ingestion of debris by a newly exposed englacial conduit. Debris stability mapping showed that 18.2–26.4% of the survey area was theoretically subject to debris remobilization. By linking changes in stability to changes in debris thickness, we observed that slopes that remain stable, stabilize, or remain unstable between periods almost exclusively show net debris thickening (mean 0.07 m a-1) whilst those which become newly unstable exhibit both debris thinning and thickening. We observe a systematic downslope increase in the rate at which debris cover thickens which can be described as a function of the topographic position index and slope gradient. Our data provide quantifiable insights into mechanisms of debris remobilization on glacier surfaces over sub-decadal timescales, and open avenues for future research to explore glacier-scale spatiotemporal patterns of debris remobilization. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd 相似文献
146.
Silcretes exposed within river-marginal or valley settings have been described in a number of studies, but few models have been suggested for the development of these ‘fluvial’ silcretes. An exception is that proposed by McCarthy and Ellery (Journal of Sedimentary Research, 1995, Vol. A65, pp. 77–90) to describe mechanisms of early stage near-surface silica diagenesis in the Okavango Delta, Botswana. This paper describes the characteristics and possible origins of massive surface and sub-surface silcretes at Samedupe and Boro Junction, beyond the distal margin of the Okavango Delta and further downstream than the sites described by McCarthy and Ellery. Morphological and petrological evidence from surface exposures and three sedimentary cores suggests that other modes of formation may also be applicable. A dual model of formation is proposed: surface silcretes are suggested to have developed by silica accumulation in seasonal pools remaining after the annual Okavango flood, whilst sub-surface horizons appear to have formed under conditions of varying pH associated with fluctuating groundwater levels beneath the channel floor. This model is reviewed in the context of the fluvial silcrete debate. © 1998 John Wiley & Sons, Ltd. 相似文献
147.
Shaw SD Brenner D Bourakovsky A Mahaffey CA Perkins CR 《Marine pollution bulletin》2005,50(10):1069-1084
Concentrations of polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and its metabolites, chlordane-related compounds (CHLs), mirex, hexachlorocyclohexane isomers (HCHs), dieldrin, and hexachlorobenzene (HCB) were determined in blubber of harbor seals (Phoca vitulina concolor) from the northwestern Atlantic coast. PCBs, DDTs, and CHLs were the major persistent organochlorines in harbor seal blubber, while mirex, HCHs, dieldrin, and HCB were minor contaminants. Highest concentrations were found in the adult males, followed by the pups, yearlings, adult females, and fetuses. DDT and PCB concentrations have declined from the high levels reported in the early 1970s, but no declines were observed in our samples over the ten-year period 1991-2001. DDT/PCB ratios were indicative of a more rapid decline of DDTs than PCBs, while ratios of p,p'-DDE/DDT were indicative of a metabolic "weathering" of DDT. The population appears to be susceptible to disease outbreaks, as evidenced by a recurrence of viral epizootics since the late 1970s. The PCB burdens in these seals are similar to levels reported in seals from polluted regions of Europe and Asia, and exceed the estimated threshold levels for adverse reproductive and immune system effects in the species. 相似文献
148.
Recent Russian legislative and policy documentation concerning national progress towards sustainable development has suggested that the attainment of such a state would represent the first stage in the development of the noosphere as outlined by the Russian scientist Vladimir Ivanovich Vernadsky (1863-1945). This paper explores Vernadsky’s model of evolutionary change through a focus on his work on the biosphere and noosphere in an attempt to further understanding of the way in which Russia is approaching the concept of sustainable development in the contemporary period. It is argued that the official Russian interpretation of the noosphere idea tends to obscure the evolutionary and materialist foundations of Vernadsky’s biosphere-noosphere conceptualisation. At the same time, the concluding section of the paper suggests that the scope of Vernadsky’s work can be used to stimulate the search for a more coherent approach to work in areas of sustainable development and sustainability across the span of the social and physical sciences. 相似文献
149.
Brian R. Shaw 《Mathematical Geology》1977,9(5):507-517
Distortion is induced in multiple linear regression by clusters of data. The magnitude of this distortion is a function of the magnitude of the mean of the clustered data. The location and estimated amount of maximum induced distortion can be obtained by evaluating the surface in question with and without clusters. The difference between these surfaces is the induced distortion. Clustering of data points is common in map data and especially in subsurface information. The Albion-Scipio Trend, an oil and gas field in Southern Michigan, has 82 percent of the available data in clusters. Evaluation of the distortion indicates that the analysis contains a measureable amount of distortion but its small magnitude does not alter the structural interpretation of the area. 相似文献
150.
Michael L. Shaw 《Solar physics》1972,27(2):436-441
A Monte Carlo technique has been used to predict the relative visibility of solar hard X-ray flares as a function of solar longitude assuming the model of Takakura and Kai to be realistic. Comparison is made with previous statistical studies of observations. A discernable longitudinal variation in the relative visibility of flares is shown to be expected but the probability of flares being visible towards the limb is shown to be higher than had previously been evident.The effect of the possible downward inclination of the particle beam with respect to the solar surface is considered. 相似文献