全文获取类型
收费全文 | 745篇 |
免费 | 29篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 42篇 |
地球物理 | 135篇 |
地质学 | 313篇 |
海洋学 | 74篇 |
天文学 | 108篇 |
综合类 | 2篇 |
自然地理 | 95篇 |
出版年
2022年 | 4篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 19篇 |
2017年 | 12篇 |
2016年 | 29篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 35篇 |
2012年 | 15篇 |
2011年 | 32篇 |
2010年 | 29篇 |
2009年 | 29篇 |
2008年 | 39篇 |
2007年 | 32篇 |
2006年 | 26篇 |
2005年 | 25篇 |
2004年 | 18篇 |
2003年 | 35篇 |
2002年 | 23篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 12篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1970年 | 3篇 |
排序方式: 共有784条查询结果,搜索用时 15 毫秒
671.
Public participation is a key ingredient of good governance and there are many advantages of involving stakeholders in the decision-making process. The European Commission identified the lack of stakeholder involvement as one of the major weaknesses of the Common Fisheries Policy (CFP). As such, the 2002 Reform of the CFP aimed to improve its system of governance by increasing the involvement of stakeholders in decision-making. Over the last decade, Scottish inshore waters have seen an increase in management measures focused on involving fishers, delegating responsibilities and decentralizing management. The present document investigates commercial inshore fishers’ perceptions of participation in the decision-making process and attitudes towards a new management regime – the Inshore Fisheries Groups (IFGs) – which aims to increase participation in and decentralization of inshore fisheries management. A survey was conducted, through face-to-face interviews, and ordered logistic and multiple regression models created to identify which characteristics influence fishers’ perceptions and attitudes. The present analysis concluded that, 5 years subsequent to the reform of the CFP, the majority of inshore fishers perceive themselves not to be consulted or involved in the decision-making process. However, and despite the fact that fishers are not completely certain of the potential of the IFGs to increase their participation in the management process, they have an overall positive attitude towards their implementation. 相似文献
672.
John R. Graham 《Geological Journal》1981,16(3):157-173
The distribution and stratigraphic relations of the Old Red Sandstone of the Clew Bay area. County Mayo are described. They comprise two groups both dominated by conglomerates, one Lower Devonian and one Middle Devonian, which have differing clast contents and which are separated by faults. The sediments are described in terms of five facies which are all interpreted as alluvial fan deposits. Provenance data from palaeocurrents and clast composition suggest transport predominantly to the west-northwest but one formation shows an opposite sense of transport. The rocks are folded about northeast-southwest axial traces and are affected by numerous faults. Structures are more complex than those of the Lower Carboniferous rocks which unconformably overlie the Devonian. A similar tectonosedimentary setting to the Old Red Sandstone of parts of the Scottish Caledonides is indicated. 相似文献
673.
Summary This paper argues that the study of crime and the fear of crime in rural areas reveals much about the geography of crime, policing and rural society. Drawing upon a crime and safety survey conducted with residents of a rural parish in Worcestershire it establishes a link between fear of crime and 'cultural threats' to residents' dominant constructions of rurality. It concludes by considering the 1998 Crime and Disorder Act and its implications for rural policing and society. 相似文献
674.
Elspeth Graham 《The Professional geographer》1999,51(1):76-89
Research traditions exert a powerful influence over the thinking of academic researchers. In population geography an entrenched empiricism and a reluctance to engage in wider debates on theory and method within human geography have resulted in a degree of separate development. Such methodological complacency has, until recently, threatened to undermine population geography's role within the discipline as a whole. Thus the discussion of multi-method research designs is of particular significance because it offers population geographers an opportunity to break out from the confines of a dominant research tradition and participate with other human geographers in an important methodological debate. This paper seeks not only to provide a critical overview of the current debate within population geography (as represented in the preceding papers in this Focus section) but also to extend that debate by raising issues of much more general concern. I argue that there are dangers in drawing the terms of the debate too narrowly. If we are to understand the nature and potential of multi-method research, we must first pose fundamental questions about the interrelationships among methods, data, and research problems. Pragmatic views on the choice of research method are inadequate because they fail to recognise the theory-driven nature of research. Only once we have achieved a better understanding of the philosophical grounding of research strategies will the opportunities afforded by multi-method research be fully realised. 相似文献
675.
J. Graham Cogley 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):497-507
Correlograms from multiple time series of point mass balance, measured on White Glacier (Axel Heiberg Island, Canada) and Abramov Glacier (Alai Range, Kirgizia), show that the correlation decreases with the difference in elevation between the points. The correlogram is used to calculate an integral spatial scale or effective sample area which, when divided into the area of the glacier, yields an estimate of the number of degrees of freedom in a stake-based estimate of the whole-glacier balance. This number – the 'effective sample size'– is a small fraction of the number of point measurements; indeed, it is independent of the number of measurements. Estimates of average balance for elevation bands are at one remove from raw stake measurements, but they are amenable to a principal component analysis which confirms that the effective sample size is very small. The small effective sample size means that uncertainty in a typical measurement of whole-glacier mass balance cannot be much less than the large value implied by the conservative assumption that stakes are perfectly correlated. One way around this difficulty would be to increase the role of prior physical understanding by seeking to model the spatial variability of mass balance. A successful model would need only a few parameters, and would allow for the joint estimation of both magnitude and uncertainty; the uncertainty in mass balance could be derived objectively from the uncertainty in the parameters. This, however, would require good estimates of the variability of mass balance at the elevation-band scale, which might in turn require that many measurement networks be redesigned. 相似文献
676.
677.
A.L. Graham 《Meteoritics & planetary science》1983,18(1):51-61
Within the chondritic matrix of Romero (H3–4) is a metal-poor inclusion consisting largely of olivines showing quench textures, minor low-Ca pyroxene and rare metal and sulphide. The olivines within this inclusion have the dominant composition Fa8 with a range Fa7, 5–17. The matrix (Romero host) olivines are, in the main, equilibrated with an average composition of Fa18, but are lower in CaO and Cr2O3 than the inclusion olivines. The high chromium content of the inclusion olivines suggests that they formed under conditions different from those represented by the other olivines in Romero. 相似文献
678.
679.
H. A. Ishii G. A. Graham A. T. Kearsley P. G. Grant C. J. Snead J. P. Bradley 《Meteoritics & planetary science》2005,40(11):1741-1747
Abstract— In January 2006, NASA's Stardust mission will return with its valuable cargo of the first cometary dust particles captured at hypervelocity speeds in silica aerogel collectors and brought back to Earth. Aerogel, a proven capture medium, is also a candidate for future sample return missions and low‐Earth orbit (LEO) deployments. Critical to the science return of Stardust as well as future missions that will use aerogel is the ability to efficiently extract impacted particles from collector tiles. Researchers will be eager to obtain Stardust samples as quickly as possible; tools for the rapid extraction of particle impact tracks that require little construction, training, or investment would be an attractive asset. To this end, we have experimented with diamond and steel microblades. Applying ultrasonic frequency oscillations to these microblades via a piezo‐driven holder produces rapid, clean cuts in the aerogel with minimal damage to the surrounding collector tile. With this approach, intact impact tracks and associated particles in aerogel fragments with low‐roughness cut surfaces have been extracted from aerogel tiles flown on NASA's Orbital Debris Collector (ODC) experiment. The smooth surfaces produced during cutting reduce imaging artifacts during analysis by scanning electron microscopy (SEM). Some tracks have been dissected to expose the main cavity for eventual isolation of individual impact debris particles and further analysis using techniques such as transmission electron microscopy (TEM) and nano‐secondary ion mass spectrometry (nanoSIMS). 相似文献
680.