全文获取类型
收费全文 | 63篇 |
免费 | 4篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 7篇 |
地球物理 | 12篇 |
地质学 | 17篇 |
海洋学 | 6篇 |
天文学 | 5篇 |
自然地理 | 13篇 |
出版年
2019年 | 2篇 |
2017年 | 2篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 4篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 1篇 |
2007年 | 1篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有67条查询结果,搜索用时 31 毫秒
41.
This paper is about the geopolitics of animal health governance. Through a biosecurity event in South Africa's pig sector we examine changes in the way the governance of disease risk is configuring intra-national spaces. Our case suggests an emerging geopolitics of animal health, one that is defined not by differences between nations but by a more complex patchwork of ‘secure’ and ‘unruly spaces’. 相似文献
42.
R.S. Martin T.A. Mather D.M. Pyle S.F.L. Watt J.A. Day S.J. Collins T.E. Wright A. Aiuppa S. Calabrese 《Journal of Volcanology and Geothermal Research》2009,179(1-2):107-119
Sweet chestnut leaves (Castanea sativa) collected from the flanks of Mt Etna volcano in 2005–2007 were analysed by inductively-coupled plasma mass spectrometry to investigate the spatial and temporal variability of element concentrations. The aim of this work was to determine whether these leaves are a bio-indicator for volcanic gas, aerosol and ash deposition and to gain new insights into the environmental effects of quiescent and eruptive volcanic plumes. Results show a positive correlation between sample variability in the concentration of elements in Castanea sativa and enrichment factors of elements in the plume. The spatial and temporal variability of chalcophilic elements (As, Cd, Cu, Mo, Tl, Zn) is consistent with prevailing winds transporting eruptive plumes to the south-east of the summit, resulting in enhanced plume deposition onto the flanks of the volcano. Similar spatial and temporal variability was found for the halide-forming elements (Cs, K, Rb) and intermediate elements (Al, Co, Mn). The spatial variability of chalcophilic, intermediate and halide-forming elements during quiescent periods was diminished (relative to eruptive periods) and could not be explained by plume deposition. In contrast, the concentrations of lithophilic elements (Ba, Ca, Mg, Sr) did not show any clear spatial variability even during eruptive periods. Comparisons between enrichment factors for elements in Castanea sativa and literature values for enrichment factors of the volcanic plume, groundwater and lichen were made. Whilst Castanea sativa offers insights into the spatial and temporal variability of deposition, the species may not be a bio-indicator for plume composition due to biological fractionation. 相似文献
43.
Dominic J. Benford Michael J. Amato John C. Mather S. Harvey Moseley Jr David T. Leisawitz 《Astrophysics and Space Science》2004,294(3-4):177-212
The Single Aperture Far-InfraRed (SAFIR) Observatory’s science goals are driven by the fact that the earliest stages of almost
all phenomena in the universe are shrouded in absorption by and emission from cool dust and gas that emits strongly in the
far-infrared (40μ–200μ) and submillimeter (200μ–1 mm). In the very early universe, the warm gas of newly collapsing, unenriched
galaxies will be revealed by molecular hydrogen emission lines at these long wavelengths. High redshift quasars are found
to have substantial reservoirs of cool gas and dust, indicative of substantial metal enrichment early in the history of the
universe. As a result, even early stages of galaxy formation will show powerful far-infrared emission. The combination of
strong dust emission and large redshift (1 < z < 7) of these galaxies means that they can only be studied in the far-infrared and submillimeter. For nearby galaxies, many
of the most active galaxies in the universe appear to be those whose gaseous disks are interacting in violent collisions.
The details of these galaxies, including the effect of the central black holes that probably exist in most of them, are obscured
to shorter wavelength optical and ultraviolet observatories by the large amounts of dust in their interstellar media. Within
our own galaxy, the earliest stages of star formation, when gas and dust clouds are collapsing and the beginnings of a central
star are taking shape, can only be observed in the far-infrared and submillimeter. The cold dust that ultimately forms the
planetary systems, as well as the cool “debris” dust clouds that indicate the likelihood of planetary sized bodies around
more developed stars, can only be observed at wavelengths longward of 20μ.
Over the past several years, there has been an increasing recognition of the critical importance of the far-infrared to submillimeter
spectral region to addressing fundamental astrophysical problems, ranging from cosmological questions to understanding how
our own Solar System came into being. The development of large, far-infrared telescopes in space has become more feasible
with the combination of developments for the James Webb Space Telescope (JWST) of enabling breakthroughs in detector technology.
We have developed a preliminary but comprehensive mission concept for SAFIR, as a 10 m-class far-infrared and submillimeter
observatory that would begin development later in this decade to meet the needs outlined above. Its operating temperature
(≤4 K) and instrument complement would be optimized to reach the natural sky confusion limit in the far-infrared with diffraction-limited
performance down to at least the atmospheric cutoff, λ {>rsim} 40 {μ}. This would provide a point source sensitivity improvement of several orders of magnitude over that of the Spitzer
Space Telescope (previously SIRTF) or the Herschel Space Observatory. Additionally, it would have an angular resolution 12
times finer than that of Spitzer and three times finer than Herschel. This sensitivity and angular resolution are necessary
to perform imaging and spectroscopic studies of individual galaxies in the early universe. We have considered many aspects
of the SAFIR mission, including the telescope technology (optical design, materials, and packaging), detector needs and technologies,
cooling method and required technology developments, attitude and pointing, power systems, launch vehicle, and mission operations.
The most challenging requirements for this mission are operating temperature and aperture size of the telescope, and the development
of detector arrays. SAFIR can take advantage of much of the technology under development for JWST, but with much less stringent
requirements on optical accuracy. 相似文献
44.
45.
K. B. Mather 《Pure and Applied Geophysics》1969,75(1):332-354
Summary The main characteristics of surface winds are tabulated for 34 Antarctic stations. Using these data, supplemented by traverse records, the average wind flow is interpolated for each region and presented as a map showing the pattern of surface wind flow for the whole continent. Attention is focused on the flow in relation to surface contours. Statistics are presented for surface slope, wind speed, temperature, seasonal variations of speed and temperature, diurnal variation (including power spectra) of the wind speed and times of maximum and minimum speed at coastal and inland stations, wind frequency versus direction, the occurrence of calms, the deviation of the plateau wind from the downslope direction, the wind direction near the front of ice shelves, the proportion of cloud cover, and wind chill factors. In all cases data are grouped according to the environs of the stations in an attempt to isolate systematic differences depending on location: coastal stations near the foot of the ice slope and fully exposed to katabatic flow, coastal stations on offshore islands, coastal stations on peninsulas, coastal stations on extensive rock areas, ice shelf stations and inland stations. 相似文献
46.
R. S. Mather 《Journal of Geodesy》1975,49(1):65-82
One of the principal problems in separating the non-tidal Newtonian gravitational effects from other forces acting on the
ocean surface with a resolution approaching the 10 cm level arises as a consequence ofall measurements of a geodetic nature being taken eitherat orto the ocean surface. The latter could be displaced by as much as ±2 m from the equipotential surface of the Earth’s gravity field corresponding
to the mean level of the oceans at the epoch of observation— i.e., the geoid. A secondary problem of no less importance is
the likelihood of all datums for geodetic levelling in different parts of the world not coinciding with the geoid as defined
above.
It is likely that conditions will be favourable for the resolution of this problem in the next decade as part of the activities
of NASA’s Earth and Ocean Physics Applications Program (EOPAP). It is planned to launch a series of spacecraft fitted with
altimeters for ranging to the ocean surface as part of this program.
Possible techniques for overcoming the problems mentioned above are outlined within the framework of a solution of the geodetic
boundary value problem to ±5 cm in the height anomaly. The latter is referred to a “higher” reference surface obtained by
incorporating the gravity field model used in the orbital analysis with that afforded by the conventional equipotential ellipsoidal
model (Mather 1974 b). The input data for the solution outlined are ocean surface heights as estimated from satellite altimetry
and gravity anomalies on land and continental shelf areas. The solution calls for a quadratures evaluation in the first instance.
The probability of success will be enhanced if care were paid to the elimination of sources of systematic error of long wavelength
in both types of data as detailed in (Mather 1973 a; Mather 1974 b) prior to its collection and assembly for quadratures evaluations. 相似文献
47.
R. S. Mather 《Journal of Geodesy》1971,45(1):65-88
Summary The alternative harmonic representations of the disturbing potential, correct to the order of the flattening, are examined
and an example is given where the incorrect use of a spherical harmonic expansion can give rise to fallacious results. The
correct usage of the spherical harmonic expansion for the disturbing potential is given in the solution of the general surface
integral to define the indirect effect in the case of the non-regularised geoid. 相似文献
48.
R. S. Mather 《Journal of Geodesy》1973,47(2):187-209
Summary A system of reference which is directly related to observations, is proposed for four dimensional studies in Earth space.
The requisite data is used to define both global control network and also polar wandering. The determination of variations
of the Earth’s gravitational field with time also forms part of such a system. Techniques are outlined for the unique definition
of the motion of the geocenter, and the changes in the location of the axis of rotation of an instantaneous Earth model, in
relation to values at some epoch of reference. The instantaneous system referred to is directly related to a fundamental equation
in geodynamics. The reference system defined would provide an unambiguous frame for long period studies in Earth space, provided
the scale of the space were specified.
Presented at the I.A.G./A.G.U. Symposium on Earth Gravity Models related problems, St Louis, Missouri, U.S.A., 16–18 August
1972. 相似文献
49.
The forest transition: a theoretical basis 总被引:17,自引:0,他引:17
Summary A theoretical basis for the forest transition (the change from contraction to expansion of national forest area) is suggested in terms of increasing agricultural adjustment to land quality. This adjustment, operating through a process of learning by farmers, results in the concentration of agricultural production in smaller areas of better land, and the agricultural abandonment of larger areas of poorer land, which are then available for reforestation through natural regeneration or planting. 相似文献
50.