全文获取类型
收费全文 | 253篇 |
免费 | 15篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 11篇 |
地球物理 | 46篇 |
地质学 | 117篇 |
海洋学 | 20篇 |
天文学 | 48篇 |
自然地理 | 22篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 9篇 |
2011年 | 24篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 21篇 |
2007年 | 12篇 |
2006年 | 17篇 |
2005年 | 13篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有274条查询结果,搜索用时 312 毫秒
141.
Tony Waltham 《Geology Today》2019,35(3):95-101
World of Geology is a book that was born from the back pages of Geology Today: a celebration of the richness of the diversity of geological sites worldwide, and a fitting tribute to the impact of a magazine that is marking its thirty‐fifth year in 2019. This photo‐feature revisits some of the spectacular images that have faetured on its back pages over the years 相似文献
142.
Tony Waltham 《Geology Today》2018,34(3):100-108
Lying just north of Los Angeles, the total collapse of the St Francis Dam in 1928 has been described as America's worst civil engineering disaster of the twentieth century. Although poorly remembered among today's residents of Los Angeles, the event is better known to engineering geologists. The dam's failure was largely due to the geology of its site, which was inappropriate to the point of disastrous, in more ways than one. 相似文献
143.
144.
Kristen Coppin Mark Halpern Douglas Scott Colin Borys James Dunlop Loretta Dunne Rob Ivison Jeff Wagg Itziar Aretxaga Elia Battistelli rew Benson rew Blain Scott Chapman Dave Clements Simon Dye Duncan Farrah David Hughes Tim Jenness Eelco van Kampen Cedric Lacey Angela Mortier Alexandra Pope Robert Priddey Stephen Serjeant Ian Smail Jason Stevens Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2008,384(4):1597-1610
A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 μm has been carried out to map the regions around several 850-μm-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared (IR) luminosities and hence star formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350-μm flux densities for 24 850-μm sources, seven of which are detected at ≥2.5σ within a 10 arcsec search radius of the 850-μm positions. When results from the literature are included the total number of 350-μm flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-IR (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich ( M dust ≃ 9 × 108 M⊙ ) , luminous ( L FIR ≃ 2 × 1012 L⊙ ) star-forming galaxies with intrinsic dust temperatures of ≃35 K and star formation rates of ≃400 M⊙ yr−1 . We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350-μm source counts, N 350 (>25 mJy) ∼ 200–500 deg−2 . 相似文献
145.
Rosalba Perna Roberto Soria Dave Pooley Luigi Stella 《Monthly notices of the Royal Astronomical Society》2008,384(4):1638-1648
Traditionally, studies aimed at inferring the distribution of birth periods of neutron stars are based on radio surveys. Here we propose an independent method to constrain the pulsar spin periods at birth based on their X-ray luminosities. In particular, the observed luminosity distribution of supernovae (SNe) poses a constraint on the initial rotational energy of the embedded pulsars, via the correlation found for radio pulsars, and under the assumption that this relation continues to hold beyond the observed range. We have extracted X-ray luminosities (or limits) for a large sample of historical SNe observed with Chandra , XMM and Swift , which have been firmly classified as core-collapse SNe. We have then compared these observational limits with the results of Monte Carlo simulations of the pulsar X-ray luminosity distribution for a range of values of the birth parameters. We find that a pulsar population dominated by millisecond periods at birth is ruled out by the data. 相似文献
146.
Climatic and tectonic controls on chemical weathering in the New Zealand Southern Alps 总被引:2,自引:0,他引:2
Climatic and tectonic controls on the relative abundance of solutes in streams draining the New Zealand Southern Alps were investigated by analyzing the elemental and Sr isotope geochemistry of stream waters, bedload sediment, and hydrothermal calcite veins. The average relative molar abundance of major cations and Si in all stream waters follows the order Ca2+ (50%) > Si (22%) > Na+ (17%) > Mg2+ (6%) > K+ (5%). For major anions, the relative molar abundance is HCO3− (89%) > SO42− (7%) > Cl− (4%). Weathering reactions involving plagioclase and volumetrically small amounts of hydrothermal calcite define the ionic chemistry of stream waters, but nearly all streams have a carbonate-dominated Ca2+ and HCO3− mass-balance. Stream water Ca/Sr and 87Sr/86Sr ratios vary from 0.173 to 0.439 μmol/nmol and from 0.7078 to 0.7114, respectively. Consistent with the ionic budget, these ratios lie solely within the range of values measured for bedload carbonate (Ca/Sr = 0.178 to 0.886 μmol/nmol; 87Sr/86Sr = 0.7081 to 0.7118) and hydrothermal calcite veins (Ca/Sr = 0.491 to 3.33 μmol/nmol; 87Sr/86Sr = 0.7076 to 0.7097).Streams draining regions in the Southern Alps with high rates of physical erosion induced by rapid tectonic uplift and an extremely wet climate contain ∼10% more Ca2+ and ∼30% more Sr2+ from carbonate weathering compared to streams draining regions in drier, more stable landscapes. Similarly, streams draining glaciated watersheds contain ∼25% more Sr2+ from carbonate weathering compared to streams draining non-glaciated watersheds. The highest abundance of carbonate-derived solutes in the most physically active regions of the Southern Alps is attributed to the tectonic exhumation and mechanical denudation of metamorphic bedrock, which contains trace amounts of calcite estimated to weather ∼350 times faster than plagioclase in this environment. In contrast, regions in the Southern Alps experiencing lower rates of uplift and erosion have a greater abundance of silicate- versus carbonate-derived cations. These findings highlight a strong coupling between physical controls on landscape development and sources of solutes to stream waters. Using the Southern Alps as a model for assessing the role of active tectonics in geochemical cycles, this study suggests that rapid mountain uplift results in an enhanced influence of carbonate weathering on the dissolved ion composition delivered to seawater. 相似文献
147.
Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest 总被引:1,自引:1,他引:0
Gabriel Katul Cheng-I Hsieh David Bowling Kenneth Clark Narasinha Shurpali Andrew Turnipseed John Albertson Kevin Tu Dave Hollinger Bob Evans Brian Offerle Dean Anderson David Ellsworth Chris Vogel Ram Oren 《Boundary-Layer Meteorology》1999,93(1):1-28
The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (u, w) and temperature (T) are more planar homogeneous than their vertical flux of momentum (u*
2) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the canonical structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the moving-equilibrium hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u*, especially when u* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (Iw) and the arrival frequency of organized structures (/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed. 相似文献
148.
S. S. Dave 《Bulletin of Volcanology》1971,35(3):619-632
The Barda group of hills represents a centre of laccolithic intrusion. The rocks encountered here are pierite basalt, rhyolite, obsidian, granophyre, felsite, aplite and diorite. There is evidence for both « Fissure Type » and « Central Volcanic Type » of igneous activity in the region, which seem to have occurred in three different phases. The parent magma has been shown to be tholeiitic in composition. The acid rocks may have been formed by crystal fractionation along with diffusion of alkalis and volatiles. The origin of diorite is attributed to a process of hybridization. 相似文献
149.
The Vale of Kashmir is an ovoid basin surrounded by Triassic limestone mountains rising to over 4000 m. At the eastern end of the Vale a group of five large karst springs occurs with a combined mean annual discharge of 9 m3/sec. Two of the springs could be supplied by their immediate limestone hinterlands. Leakage from clastic rocks into the limestone mass must partially supply two other springs. A dye test was carried out to confirm the hydrologic connection between the fifth spring and sinks along the bank of the Bringi River, 14 km from this spring. There was no structural or lithologic control for the spring positions, which were at the lowest hydrologic points of the limestone blocks. 相似文献
150.