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191.
lt is shown that Maxwell's equations which describe the propagation of electromagnetic radiation are analogous to the kinematic relationships which govern the propagation of long water waves, if the latter equations are described in terms of a vector potential. The analogy between the two phenomena may be used to study, for example, seiching, or long wave resonance, in harbors by means of an equivalent microwave cavity. The plan geometry of the cavity would be geometrically similar to that of the harbor basin so that wave reflections were correctly reproduced, and the refraction caused by depth variations in the harbor would be modeled by varying the dielectric properties of the cavity interior. When supplied with an appropriate source of microwaves, the intensity of the electric field at a given point can be related to wave induced currents at a similar location in the harbor. Such information is an important factor in the siting of berthing and mooring facilties for shipping. It is also shown how the impedance concept can be used to study the transformation of long waves as they traverse a step change in water depth. 相似文献
192.
J. D. Peacock W. E. N. Austin I. Selby D. K. Graham R. Harland I. P. Wilkinson 《第四纪科学杂志》1992,7(2):145-161
Examination of two radiocarbon-dated vibrocores taken from south of St Kilda at a water depth of about 155 m, a short distance within the maximum position of the Late Devensian (Dimlington Stadial) ice sheet, suggests that the St Kilda Basin became free of glacier ice after 15250 yr BP. Sedimentation in a shallow, low energy, high arctic, muddy environment continued until after 13500 yr BP. There followed a higher energy temperate episode during which water depths were roughly about 40 m: this is correlated with the latter part of the Windermere Interstadial and with the warmer interval known in shallow Scottish seas about or a little before 11 000 yr BP. The Loch Lomond (Younger Dryas) Stadial is marked in the vibrocores by the return of muddy sediments and a cold-water fauna. Relatively shallow water conditions seem to have persisted into the earliest Flandrian, when the water depth was still roughly 60 m, corresponding to a sea-level in the area 90–100 m below present. It is suggested that pack ice was widespread in the northeast Atlantic before the Windermere Interstadial and also during the Loch Lomond Stadial, when it transported shards of Icelandic volcanic ash into the St Kilda basin. Estimates of sea-surface temperature for the last part of the Windermere Interstadial are close to those derived from the deep-sea record for the same period. 相似文献
193.
S. M. Hill V. J. Pizzo C. C. Balch D. A. Biesecker P. Bornmann E. Hildner L. D. Lewis R. N. Grubb M. P. Husler K. Prendergast J. Vickroy S. Greer T. Defoor D. C. Wilkinson R. Hooker P. Mulligan E. Chipman H. Bysal J. P. Douglas R. Reynolds J. M. Davis K. S. Wallace K. Russell K. Freestone D. Bagdigian T. Page S. Kerns R. Hoffman S. A. Cauffman M. A. Davis R. Studer F. E. Berthiaume T. T. Saha G. D. Berthiume H. Farthing F. Zimmermann 《Solar physics》2005,226(2):255-281
The Solar X-ray Imager (SXI) was launched 23 July 2001 on NOAAs GOES-12 satellite and completed post-launch testing 20 December 2001. Beginning 22 January 2003 it has provided nearly uninterrupted, full-disk, soft X-ray solar images, with a continuous frame rate significantly exceeding that for previous similar instruments. The SXI provides images with a 1 min cadence and a single-image (adjustable) dynamic range near 100. A set of metallic thin-film filters provides temperature discrimination in the 0.6 – 6.0 nm bandpass. The spatial resolution of approximately 10 arcsec FWHM is sampled with 5 arcsec pixels. Three instrument degradations have occurred since launch, two affecting entrance filters and one affecting the detector high-voltage system. This work presents the SXI instrument, its operations, and its data processing, including the impacts of the instrument degradations. A companion paper (Pizzo et al., this issue) presents SXI performance prior to an instrument degradation that occurred on 5 November 2003 and thus applies to more than 420000 soft X-ray images of the Sun. 相似文献
194.
Clive Wilkinson 《Climatic change》2005,73(1-2):155-167
The large-scale study of ship's logbooks for climatic data has revealed the wide and varied potential of this under-exploited
resource for the study of the past. As well as being of utility to climatologists, the daily recording of shipboard information
can help illuminate a number of themes of interest to maritime and naval historians. More than this, however, such studies
can help inform both more general and other specialized historical studies. Logbooks contain both anecdotal and statistical
data relevant to the studies of medical historians, the history of science and navigation, social history, economic history,
warfare, imperial history and of course environmental history. Moreover, many of these themes can be studied in a multi-national
context and furthermore, if studied in a multi-disciplinary context, can offer many useful insights. 相似文献
195.
The use of the simple genetic algorithm in finding the critical factor of safety in slope stability analysis 总被引:11,自引:0,他引:11
A simple genetic algorithm (SGA) is applied to the search for the minimum factor of safety in slope stability analysis. The method is shown to be superior to simple optimisation routines, which can find false minima, and to ‘brute force’ approaches, which require the analysis of a very large number of possibilities. An approach to implementing SGA is defined and refined, indicating principles which may be used in applying the method to other engineering problems. 相似文献
196.
An alkali basalt near Glen Innes, northeastern New South Wales, contains a suite of Cr-diopside group ultramafic xenoliths
which includes some spinel peridotites but which is dominated by a diverse spinel pyroxenite assemblage. Pyroxenite xenoliths
range from subcalcic clinopyroxenites (composed largely of unmixed prismatic subcalcic clinopyroxene megacrystals and lesser
orthopyroxene megacrystals) to equant mosaic textured websterites (orthopyroxene and Ca-rich clinopyroxene ± spinel). Rare
orthopyroxenite xenoliths also occur. The pyroxenite xenoliths are characterised by high 100Mg/(Mg + Fe2+) ratios (M˜ 90) and low concentrations of Ti, K, P, La, Ce and Zr. The websterites are mineralogically and chemically similar to many
spinel pyroxenites occurring as layers or dykes in peridotite massifs such as those at Ronda in southern Spain and at Ariège
(French Pyrénées). T / P estimates indicate crystallization temperatures of 1250–1350 °C for subcalcic clinopyroxene-orthopyroxene megacrystal pairs
and 900–1000 °C for the equilibrated mosaic textured websterites and associated peridotites at pressures of 9–13 kbar. Subcalcic
clinopyroxene megacrystals, websterites and orthopyroxenites have LREE-depleted chondrite-normalised REE abundances with (La/Yb)CN < 1 and their convex-upwards REE patterns are typical of subcalcic clinopyroxene-dominated cumulates. The pyroxenites are
not residua from partially melted pyroxenite layers or dykes in mantle peridotites nor are they completely crystallized protobasaltic
or protopicritic magmas. They are interpreted as high-pressure crystal segregations from basaltic magmas (probably mildly
alkaline or transitional) flowing within narrow mantle conduits (the flow crystallization model of Irving, 1980). The parental
magma(s) was Ti-poor (0.6–0.7% TiO2) and relatively Mg-rich (M˜ 74 − 70). Pyroxenite genesis was a two-stage process involving crystallization of tschermakitic subcalcic clinopyroxenes
and orthopyroxenes ±spinel as liquidus or near-liquidus phases at 1250–1350 °C and 9–13 kbar to yield “primary” subcalcic
clinopyroxenites which then re-equilibrated at 900–1000 °C and similar pressures to produce the mosaic textured “secondary”
websterites. The pyroxenites show a wide range of 143Nd/144Nd and 87Sr/86Sr values (0.513298–0.512473 and 0.702689–0.704659, respectively). Their isotopic ratios appear to have been variably modified
by exchange with adjacent mantle peridotites or migrating basaltic melts.
Received: 11 December 1995 / Accepted: 3 December 1996 相似文献
197.
198.
Thermal spallation is a method whereby the surface of a rock is rapidly heated causing small (100–1000 m) flakes or spalls, to form. When applied to drilling, a supersonic, high temperature (2600 K) gas jet is directed at the rock to provide the heat source and sweep away the spalls.Previous studies of thermal spallation drilling indicate that penetration rates of up to 30 m/hr (100 ft/hr), approximately ten times greater than commonly obtained using conventional rotary mechanical methods, can be achieved in competent, non-fractured hard rock such as granite. A total direct operating cost for drilling in granite using a flame-jet spallation drill was estimated by Browning (1981) to be approximately 9/m in 19919/m in 1991 (about 3/ft) compared to < img src="/content/K51317H7246T8K15/xxlarge8220.gif" alt="ldquo" align="MIDDLE" border="0»trouble-free < img src="/content/K51317H7246T8K15/xxlarge8221.gif" alt="rdquo" align="MIDDLE" border="0» well drilling costs for conventional rotary methods in similar rock to depths of 3 to 7 km (10000 to 21000 ft) of3/ft) compared to trouble-free well drilling costs for conventional rotary methods in similar rock to depths of 3 to 7 km (10000 to 21000 ft) of 300 to 900/m (900/m (100 to $300/ft) (Tester and Herzog, 1990, 1992). The Browning estimates for spallation drilling are obviously optimistic in that they don't include capital costs for the rig and associated hardware. However, the substantially higher penetration rates, significantly reduced wear of downhole components, and the high efficiency of rock communition in comparison to rotary methods suggest that substantial cost reductions could be possible in deep drilling applications. For example, in the construction of hot dry rock geothermal power plants where rotary mechanical methods are used for well drilling to depths of (4 to 5 km), about half of the initial capital cost would be required for well drilling alone (Tester and Herzog, 1992). 相似文献
199.
E. Xanthopoulos I. W. A. Browne L. J. King L. V. E. Koopmans N. J. Jackson D. R. Marlow A. R. Patnaik R. W. Porcas & P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》1998,300(3):649-655
We report the discovery of a new double-image gravitational lens system, B1030 + 074, which was found during the Jodrell Bank–VLA Astrometric Survey (JVAS). We have collected extensive radio data on the system using the VLA, MERLIN, the EVN and the VLBA, and optical observations using WFPC2 on the HST . The lensed images are separated by 1.56 arcsec and their flux density ratio at centimetric wavelengths is approximately 14:1, although the ratio is slightly frequency-dependent and the images appear to be time-variable. The HST pictures show both the lensed images and the lensing galaxy close to the weaker image. The lensing galaxy has substructure which could be a spiral arm or an interacting galaxy. We have modelled B1030 + 074 using a singular isothermal ellipsoid which yields a time delay of 156/ h 50 d. This lens is likely to be suitable for the measurement of the Hubble constant. 相似文献
200.
A method for evaluating statistical errors associated with logarithmic velocity profiles 总被引:3,自引:0,他引:3
R. H. Wilkinson 《Geo-Marine Letters》1984,3(1):49-52
A logarithmic velocity profile is often fitted to velocity data in order to calculate the friction velocity (u
*) and typify the surface texture by a roughness length (z
o
). A method is given for estimating the errors in these parameters as calculated by this method. An example is given in which
the size of the error is compared with the fluctuations that typically occur in the time seriesu
*(t) andz
o
(t). 相似文献