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排序方式: 共有794条查询结果,搜索用时 12 毫秒
731.
Massimiliano Galeazzi Meng Chiao Michael R. Collier Thomas Cravens Dimitra Koutroumpa Kip D. Kuntz Susan Lepri Dan McCammon Frederick S. Porter Krishna Prasai Ina Robertson Steve Snowden Youaraj Uprety 《Experimental Astronomy》2011,32(2):83-99
The Diffuse X-rays from the Local galaxy (DXL) mission is an approved sounding rocket project with a first launch scheduled around December 2012. Its goal is to identify and separate the X-ray emission generated by solar wind charge exchange from that of the local hot bubble to improve our understanding of both. With 1,000 cm2 proportional counters and grasp of about 10 cm2 sr both in the 1/4 and 3/4 keV bands, DXL will achieve in a 5-min flight what cannot be achieved by current and future X-ray satellites. 相似文献
732.
Susan M. P. McKenna-Lawlor 《Solar physics》2011,272(2):257-299
During the International Geophysical Year (IGY, 1957/1958) Dunsink Observatory near Dublin in Ireland was a World Data Centre
for Solar Activity. In this circumstance, Hα Lyot Heliograph records secured on a daily basis between 07:00 – 14:00 UT at
the Cape of Good Hope (then an integral link in a network of similar instruments contributing during the IGY to global monitoring
of solar chromospheric activity) were routinely sent to Dunsink for analysis and dissemination. The investigations carried
out at Dunsink on these data resulted, inter alia, in the discovery of the Flare Nimbus phenomenon. The nimbus comprises a dark expanding halo seen in the plage regions around
major flares at, or within a few minutes of, the time of flare maximum intensity in Hα light. It reaches its greatest extent
about 30 minutes after flare maximum. Its maximum dimensions (estimated visually) lie in the range 2 – 4×105 km and its duration ranges from ∼ 1 – 2 hours. Within the nimbus the striation pattern is either completely destroyed or
loses its pre-flare configuration. An account of this phenomenon and its interpretation appeared primarily, although not exclusively,
in the locally produced Dunsink Observatory Publications which are not now easily accessible to the world community of solar researchers. Also, at around the time when the nimbus
was first identified and recorded in Lyot Heliograph data at several observatories, techniques in solar physics shifted towards
high resolution narrow field observations. Under these conditions no further examples of the nimbus were recorded and the
subject has remained dormant over several decades. The present paper again places the scientific results obtained with regard
to the nimbus in the public domain, together with an account of the evolution within the scientific community of an explanation
of this phenomenon. It is suggested here for the first time, in the light of present day data concerning coronal mass ejections
(CMEs) and coronal dimming, that the nimbus provides a signature of CME-related reorganization of the magnetic field in the
chromosphere (such that the transverse magnetic field component decreases and transforms into the line of sight component
as the vector field stretches out). Coronal dimming provides a complementary signature of CME-related mass depletion in the
corona. 相似文献
733.
The discovery of plumes of H2O vapor and ice particles erupting from the south pole of Enceladus, the tiny frigid satellite of Saturn, sparked controversy over whether these plumes are produced by boiling, or by sublimation with subsequent recondensation of the sublimated vapor [Porco, C.C., Helfenstein, P., Thomas, P.C., Ingersoll, A.P., Wisdom, J., West, R., Neukum, G., Denk, T., Wagner, R., Roatsch, T., Kieffer, S., Turtle, E., McEwen, A., Johnson, T.V., Rathbun, J., Veverka, J., Wilson, D., Perry, J., Spitale, J., Brahic, A., Burns, J.A., DelGenio, A.D., Dones, L., Murray, C.D., Squyres, S., 2006. Science 311, 1393-1401]. Porco et al.’s analysis that the masses of ice (I) and vapor (V) in the plume were comparable was taken to argue against the occurrence of sublimation and recondensation, leading to the hypothesis that the reservoir was boiling water, possibly as close as 7 m to the surface. Thus, it has been advocated that Enceladus should be a target for astrobiology exploration. Here we show, with recalculations using the original data and methodologies, as well as with new sensitivity studies, that the mass of ice in the column is significantly less than the mass of water vapor, and that by considering three additional effects, I/V is likely to be <0.2-0.1. This means that the plume is dominated by vapor that the thermodynamics permits to be easily produced by sublimation with recondensation. The low I/V ratio provides no compelling criterion for consideration of a liquid water reservoir. The uncertainties on the I/V ratio have not previously been discussed in the literature. Although the I/V ratio is sensitive to particle sizes and size distributions, the masses of ice (I) and vapor (V) are not comparable in any scenario constrained by available observations. We thus discuss the implications of sublimation from a thermodynamic point of view in a context that has not been presented previously. Constraints on I/V ratio from future spacecraft measurements of the plume, in conjunction with consideration of the total plume composition and multicomponent analysis, can help constrain source conditions for the plume. 相似文献
734.
735.
Every year the Earth crosses or passes near one of the dust trails left by Comet 55P/Tempel-Tuttle in its pass through the Solar System every 33.2 years. This produces a meteor shower Commonly called the Leonid. The 2001 Leonid meteor shower is one of the strongest in recent years. We present observations made by the 50 MHz all-sky meteor radar located at the Platteville Atmospheric Observatory in Colorado (40° N, 105° W). The spatial and temporal distributions of the meteor activity detected by the radar during the 2001 Leonid shower differs from the observed sporadic activity detected by VHF radars. Estimation of the radiant flux of the meteor shower of the shower by a well-known methodology is presented, and the intensity of the phenomena is discussed. 相似文献
736.
Paul A. Scowen Mario R. Perez Susan G. Neff Dominic J. Benford 《Experimental Astronomy》2014,37(1):11-35
Following several recommendations presented by the Astrophysics Decadal Survey 2010 centered around the need to define “a future ultraviolet-optical space capability”, on 2012 May 25, NASA issued a Request for Information (RFI) seeking persuasive ultraviolet (UV) and visible wavelength astrophysics science investigations. The goal was to develop a cohesive and compelling set of science objectives that motivate and support the development of the next generation of ultraviolet/visible space astrophysics missions. Responses were due on 10 August 2012 when 34 submissions were received addressing a number of potential science drivers. A UV/visible Mission RFI Workshop was held on 2012 September 20 where each of these submissions was summarized and discussed in the context of each other. We present a scientific analysis of these submissions and presentations and the pursuant measurement capability needs, which could influence ultraviolet/visible technology development plans for the rest of this decade. We also describe the process and requirements leading to the inception of this community RFI, subsequent workshop and the expected evolution of these ideas and concepts for the remainder of this decade. 相似文献
737.
738.
The City West Urban Strategy is concerned with redevelopment in part of inner metropolitan Sydney. Such plans should not be seen in isolation, but in a wider temporal and spatial context. Pyrmont and Ultimo have been undergoing significant socioeconomic changes for a decade and this trend is likely to be reinforced and intensified if the Strategy is implemented. Also the recent and projected changes are consistent with a global pattern of restructuring in urban waterfront areas where former port and industrial functions have declined. 相似文献
739.
740.