全文获取类型
收费全文 | 565篇 |
免费 | 32篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 36篇 |
地球物理 | 123篇 |
地质学 | 219篇 |
海洋学 | 59篇 |
天文学 | 90篇 |
综合类 | 1篇 |
自然地理 | 62篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 5篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 26篇 |
2014年 | 19篇 |
2013年 | 24篇 |
2012年 | 28篇 |
2011年 | 38篇 |
2010年 | 42篇 |
2009年 | 39篇 |
2008年 | 25篇 |
2007年 | 34篇 |
2006年 | 27篇 |
2005年 | 27篇 |
2004年 | 30篇 |
2003年 | 21篇 |
2002年 | 15篇 |
2001年 | 9篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
排序方式: 共有603条查询结果,搜索用时 31 毫秒
41.
Arthur Rodgers Hrvoje Tkalcic David McCallen Shawn Larsen Catherine Snelson 《Pure and Applied Geophysics》2006,163(1):55-80
We report site response in Las Vegas Valley (LVV) from historical recordings of Nevada Test Site (NTS) nuclear explosions
and earthquake recordings from permanent and temporary seismic stations. Our data set significantly improves the spatial coverage
of LVV over previous studies, especially in the northern, deeper parts of the basin. Site response at stations in LVV was
measured for frequencies in the range 0.2–5.0 Hz using Standard Spectral Ratios (SSR) and Horizontal-Vertical Spectral Ratios
(HVR). For the SSR measurements we used a reference site (approximately NEHRP B ``rock' classification) located on Frenchman
Mountain outside the basin. Site response at sedimentary sites is variable in LVV with average amplifications approaching
a factor of 10 at some frequencies. We observed peaks in the site response curves at frequencies clustered near 0.6, 1.2 and
2.0 Hz, with some sites showing additional lower amplitude peaks at higher frequencies. The spatial pattern of site response
is strongly correlated with the reported depth to basement for frequencies between 0.2 and 3.0 Hz, although the frequency
of peak amplification does not show a similar correlation. For a few sites where we have geotechnical shear velocities, the
amplification shows a correlation with the average upper 30-meter shear velocities, V30. We performed two-dimensional finite difference simulations and reproduced the observed peak site amplifications at 0.6 and
1.2 Hz with a low velocity near-surface layer with shear velocities 600–750 m/s and a thickness of 100–200 m. These modeling
results indicate that the amplitude and frequencies of site response peaks in LVV are strongly controlled by shallow velocity
structure. 相似文献
42.
Lisa K. Whalley Kate L. Furneaux Tom Gravestock Helen M. Atkinson Catherine S. E. Bale Trevor Ingham William J. Bloss Dwayne E. Heard 《Journal of Atmospheric Chemistry》2007,58(1):19-39
A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere.
An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of
the IO A2Π3/2 ← X2Π3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument
was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N2O/CF3I/N2 mixtures with O3 actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration
period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer)
campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured
significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing
the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum
at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF. 相似文献
43.
Catherine H. Yansa 《Journal of Paleolimnology》1998,19(4):429-441
The Andrews site represents one of countless prairie potholes found in areas of hummocky moraine on the northern Great Plains. Sediments from a depth of 5.8 to 3.1 m at this 'kettle-fill' site in the Missouri Coteau upland of southern Saskatchewan, Canada, provides a record of vegetation, climate, and hydrologic changes within a small, ca 30 m diameter, closed-drainage basin from ca 10.2 to 5.8 ka. Plant macrofossil analyses of 67 samples, 6 14C ages, and stratigraphy were used to identify 5 zones, representing the paleohydrological changes that followed deglaciation in southern Saskatchewan.Results of this study indicate that with the melting of residual stagnant ice a pond (>2 m deep) with abundant aquatic, emergent, and shoreline plants developed in the basin at ca 10.2 ka and persisted until at least ca 8.8 ka. During this time there was a shift in upland vegetation from a white spruce forest (Zone II) to a deciduous parkland at ca 10 ka (Zone III). As climate warmed, brackish and alkaline conditions developed coincident with shallowing of the pond at the end of Zone III. The perennial water phase ended at ca 8.8 ka and was followed by a low-water stand lasting ca 1100 years. Prairie fires and slopewash from unstable slopes were dominant sedimentological processes until ca 7.7 ka (Zone IV). Water levels began to rise and between ca 7.7 and 5.8 ka a semi-permanent pond was established in a grassland setting (Zone V). After ca 5.8 ka this prairie pothole wetland became ephemeral, to the point that plant macrofossils could not be preserved, a situation continuing today. Interactions between climate change, variability in local groundwater supply, and sedimentological processes likely account for the paleohydrologic events reconstructed at the Andrews site. 相似文献
44.
45.
Catherine Rhein 《GeoJournal》1998,46(1):51-62
Which places are left to minorities in the housing and labour markets in metropolitan Paris? Over the last two decades, job structures have evolved dramatically, eroding the formerly prominent Paris working-class, shaking the social and political roots of its identity. These indicators would lead one to diagnose a growing fragmentation of metropolitan society. In the political debate, the burning issue of the crisis of suburbs has replaced outdated debate of the class struggle. This paper aims first to re-examine the interactions between social status and national origins, then analyses the housing conditions of different social strata, and finally demonstrates the pre-eminence of social status over national origins in the pattern of residential segregation. 相似文献
46.
Tunicates may serve as marine pollution indicators for monitoring the release of industrial and/or radioactive wastes into the marine environment. Their ability to accumulate certain trace elements from the seawater can be employed in order to define a suitable organism as indicator for some specific pollutants. In this work the concentration of the elements cobalt, zinc, chromium, caesium, silver, iron, rubidium, selenium, scandium and antimony has been determined by instrumental neutron activation analysis and γ-ray spectroscopy, in two tunicates, Microcosmus sulcatus (Pyuridae) and Ciona intestinalis (Cionidae).According to the concentration factors found for these species Ciona intestinalis can be used as indicator for iron, while Microcosmus sulcatus as indicator for the elements selenium, chromium, zinc and cobalt. 相似文献
47.
C. Brocksopp J. C. A. Miller-Jones R. P. Fender B. W. Stappers 《Monthly notices of the Royal Astronomical Society》2007,378(3):1111-1117
XTE J1748−288 is a black hole X-ray transient which went into outburst in 1998 June. The X-ray light curves showed canonical morphologies, with minor variations on the 'fast rise exponential decay' profile. The radio source, however, reached an unusually high flux density of over 600 mJy. This high radio flux was accompanied by an exceptional (>20 per cent) fractional linear polarization, the variability of which was anticorrelated with the flux density. We use this variability to discuss possible depolarization mechanisms and to predict the underlying behaviour of the (unresolved) core/jet components. 相似文献
48.
Rhiannon G. MAYNE Jessica M. SUNSHINE Harry Y. McSWEEN Timothy J. McCOY Catherine M. CORRIGAN Allison GALE 《Meteoritics & planetary science》2010,45(7):1074-1092
Abstract– We investigate the relationship between the petrology and visible–near infrared spectra of the unbrecciated eucrites and synthetic pyroxene–plagioclase mixtures to determine how spectra obtained by the Dawn mission could distinguish between several models that have been suggested for the petrogenesis of Vesta’s crust (e.g., partial melting and magma ocean). Here, we study the spectra of petrologically characterized unbrecciated eucrites to establish spectral observables, which can be used to yield mineral abundances and compositions consistent with petrologic observations. No information about plagioclase could be extracted from the eucrite spectra. In contrast, pyroxene dominates the spectra of the eucrites and absorption band modeling provides a good estimate of the relative proportions of low‐ and high‐Ca pyroxene present. Cr is a compatible element in eucrite pyroxene and is enriched in samples from primitive melts. An absorption at 0.6 μm resulting from Cr3+ in the pyroxene structure can be used to distinguish these primitive eucrites. The spectral differences present among the eucrites may allow Dawn to distinguish between the two main competing models proposed for the petrogenesis of Vesta (magma ocean and partial melting). These models predict different crustal structures and scales of heterogeneity, which can be observed spectrally. The formation of eucrite Allan Hills (ALH) A81001, which is primitive (Cr‐rich) and relatively unmetamorphosed, is hard to explain in the magma ocean model. It could only have been formed as a quench crust. If the magma ocean model is correct, then ALHA81001‐like material should be abundant on the surface of Vesta and the Vestoids. 相似文献
49.
50.
We investigate a new theory of the origin of the irregular satellites of the giant planets: capture of one member of a ∼100-km binary asteroid after tidal disruption. The energy loss from disruption is sufficient for capture, but it cannot deliver the bodies directly to the observed orbits of the irregular satellites. Instead, the long-lived capture orbits subsequently evolve inward due to interactions with a tenuous circumplanetary gas disk.We focus on the capture by Jupiter, which, due to its large mass, provides a stringent test of our model. We investigate the possible fates of disrupted bodies, the differences between prograde and retrograde captures, and the effects of Callisto on captured objects. We make an impulse approximation and discuss how it allows us to generalize capture results from equal-mass binaries to binaries with arbitrary mass ratios.We find that at Jupiter, binaries offer an increase of a factor of ∼10 in the capture rate of 100-km objects as compared to single bodies, for objects separated by tens of radii that approach the planet on relatively low-energy trajectories. These bodies are at risk of collision with Callisto, but may be preserved by gas drag if their pericenters are raised quickly enough. We conclude that our mechanism is as capable of producing large irregular satellites as previous suggestions, and it avoids several problems faced by alternative models. 相似文献