全文获取类型
收费全文 | 456篇 |
免费 | 17篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 43篇 |
地球物理 | 89篇 |
地质学 | 184篇 |
海洋学 | 22篇 |
天文学 | 97篇 |
自然地理 | 38篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 7篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 36篇 |
2012年 | 13篇 |
2011年 | 21篇 |
2010年 | 11篇 |
2009年 | 19篇 |
2008年 | 20篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1971年 | 6篇 |
1969年 | 2篇 |
排序方式: 共有480条查询结果,搜索用时 17 毫秒
241.
Geology of the saucer-shaped sill near Mahad, western Deccan Traps, India, and its significance to the Flood Basalt Model 总被引:1,自引:0,他引:1
An ~22-m-thick saucer-shaped sill occurs near Mahad and is exposed as a curvilinear, miniature ridge within the Deccan Traps. The sill has variable dips (42–55°). It has a 7.1-km long axis and 5.3 km short axis (aspect ratio of 1.4) and is larger than the MV sill of the Golden Valley sill complex, South Africa and the Panton sill, Australia. The sill has distinct glassy upper and lower chilled margins with a coarse-grained highly jointed core. The samples from the margin are invariably fractured and iron stained because of deuteric alteration. The rock from the sill is plagioclase-phyric basalt. At least three thick sill-like apophyses emanate from the base of the main sill. The apophyses change direction because of bending and thinning from a horizontal concordant sheet at the top to a discordant inclined form that bends again to pass into a lower horizontal concordant sheet. We interpret such features as ‘nascent saucer-shaped sills’ that did not inflate to form nested sills. Geochemically, the sill consists of poorly differentiated tholeiitic basalt that has a restricted geochemical range. Critical trace element ratios and primitive mantle normalised trace and REE patterns indicate that the sills have geochemical affinities to the Poladpur chemical type and that the pahoehoe flow they intrude belongs to the Bushe Formation. Calculated magmatic overpressures during sill emplacement range from 8.4 to 11.3 MPa (for Young’s modulus E?=?5 GPa) and 16.7 to 22.5 MPa (for E=10 GPa) and depth to magma chamber ranges from 8.5 to 11.5 km (E?=?5 GPa) and 17.1 to 22.9 km (E?=?10 GPa), consistent with petrological and gravity modelling. The volume of the Mahad sill is approximately 276 km3 and is constant irrespective of the variations in the values of host-rock Young’s modulus. In 1980, Cox (J Petrol 21:629–650, 1980) proposed a conceptual model of the crust–mantle section beneath the Karoo CFB which is considered as the fundamental model for flood basalt volcanism. Our paper confirms the presence of a sill plus the inferred substructure beneath Mahad that are compatible with predictions of that model. In LIPS, saucer-shaped sills are formed in areas experiencing extensional tectonics where processes such as the Cook–Gordon delamination and Dundurs elastic extensional mismatch between layered sedimentary rocks or lava flows are responsible for the deflection of dykes into sills. A similar process is envisaged for the formation of the Mahad sill. 相似文献
242.
Raymond Hide 《地球物理与天体物理流体动力学》2013,107(1-3):69-79
Abstract ‘‘Helicity'’ density H ≡ u · ω and other pseudo-scalar fields such as P ≡ ω · Vlnρ (which is related to Ertel potential vorticity) are useful quantities in theoretical fluid dynamics and magneto-fluid dynamics. Here u denotes the Eulerian flow velocity relative to the chosen frame of reference, ω ≡ V × u is the corresponding relative vorticity and ρ the mass density of the fluid. A general expression is readily obtained for ?H/?t (where t denotes time) in terms of P and the ‘‘superhelicity'’ density S ≡ ω · V × ω which, in fluids of low viscosity, has its highest values in boundary layers. One need for such a relationship became evident during an attempt to interpret the findings of laboratory experiments on thermal convection in rotating fluids in containers of various geometrical shapes and topological characteristics. In electrodynamics an analogous expression can be found relating the time rate of change of ‘‘magnetic helicity'’ A · B to ‘‘magnetic superhelicity'’ B · ? × B (where B · ? × A is the magnetic field) and a scalar quantity analogous to P which involves non-Ohmic contributions to the relationship between the electric current density and the electric field. 相似文献
243.
J.C. Raymond 《Astronomische Nachrichten》2012,333(4):305-308
Most of the energy in a solar flare, and presumably a stellar flare as well, takes the form of a power law of energetic particles. The energetic electrons produce a bremsstrahlung continuum, while the most energetic nuclei produce gamma‐rays. Nuclei around 1 MeV/AMU can produce X‐rays during and after charge transfer with neutrals. This paper predicts the fluxes for some prominent X‐ray lines and compares them to existing spectra (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
244.
Raymond Jonckheere Daniel Heinz Bradley R. Hacker David Rafaja Lothar Ratschbacher 《地学学报》2019,31(3):263-270
This contribution reports Raman radiation damage measurements of zircons from the Kontinentale Tiefbohrung, on the western border of the Bohemian Massif. The mean wavenumbers (ω3) and widths (Γ3) of the ν3(SiO4) Raman band are constant down to 3 km, decrease (ω3) resp. increase (Γ3) between 3 and 5 km, and are again constant between 5 and 7 km. Uniform high Γ3 values associated with ω3 values close to those of undamaged zircon between 5 and 7 km are interpreted as due to residual damage predating the exhumation of the Bohemian Massif. A superimposed post‐exhumation signal indicates full damage retention down to 3 km depth, partial annealing between 3 and 5 km, and zero retention at greater depth. An attempt to calculate radiation damage ages gives results of a meaningful order of magnitude but also exposes difficulties associated with dating basement samples with complex damage accumulation and annealing histories. 相似文献
245.
Raymond S. Eilertsen Louise Hansen Terje H. Bargel Inger-Lise Solberg 《Geomorphology》2008,93(3-4):548-562
The distribution of a large number of clay slides in the Målselv valley, northern Norway, is analysed and put into context with the stratigraphic organization of the valley-fill sediments. About 32% of the landslides larger than 104 m3 occur close to the valley margins, where mud is either exposed or at shallow depth. About 57% of the landslides occur mid-valley, where relatively thin (< 15 m) coarse-grained deltaic sediments overlay fine-grained marine and glaciomarine sediments, and about 11% of the landslides occur in front of ice-contact deposits. The slide-prone areas are all characterized by the occurrence of heterogeneous sediments (interbedded clay, silt and sand), in addition to the presence of steep slopes eroded by rivers. The heterogeneous nature of the sediments probably enhanced groundwater drainage and leaching of salts from the clay, increasing sensitivity. Thus, the distribution and organization of the valley-fill sediments and groundwater drainage probably controlled the position of the slide scars and sliding planes. Since deglaciation of the valley (11,500 BP–present), isostatic rebound has enhanced fluvial incision and the creation of steep slopes due to a fall in relative sea level of up to 80 m.Arcuate-shaped, ‘bottleneck’ landslide scars ranging from c. 104 to 107 m3 in size is the dominant morphological signature of the slides, typical for quick clay slides or earth flows involving fluid mud. Their most common triggering mechanism is probably erosion at the toe slopes by the river Målselv or its tributaries. River erosion close to the valley margin, where glaciomarine and marine sediments are present, seems to give the most severe slides. The overall valley-fill organization controls the distribution of clay slides, which may apply to other fjord valleys having similar sediment distribution. 相似文献
246.
Climate change impacts on bedload transport in alpine drainage basins with hydropower exploitation 下载免费PDF全文
Mélanie Raymond Pralong Jens Martin Turowski Dieter Rickenmann Massimiliano Zappa 《地球表面变化过程与地形》2015,40(12):1587-1599
Sediment transport is known to have a significant impact on hydropower infrastructures and changes in sediment transport rates are important for sediment management measures and hydroelectricity production. In this study, we present how climate change may affect bedload transport in 66 high alpine catchments used by hydropower companies in the Valais, Switzerland. Future sediment yield is estimated with a runoff‐based sediment transport model for the two future 30 year time periods 2021–2050 and 2070–2099. The analysis is integrated into a modelling chain in which error‐corrected and downscaled climate scenarios generated in the framework of the ENSEMBLES project are coupled to the hydrological model PREVAH, glacier retreat and bedload transport. To calibrate the sediment transport model, we used the observed sediment volumes in water intakes and reservoirs if such data were available. The results obtained show on average a decrease of sediment yield due to the reduced runoff generation during summer, especially for the scenario period 2070–2099. A shift of the seasonal sediment transport regime with a current maximum during July and August to earlier months in the year is predicted. Projections of future sediment yield rely on the accuracy of the individual modeling chain elements. The different sources of uncertainty are discussed qualitatively. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
247.
Thierry Appourchaux Raymond Burston Yanbei Chen Michael Cruise Hansjörg Dittus Bernard Foulon Patrick Gill Laurent Gizon Hugh Klein Sergei Klioner Sergei Kopeikin Hans Krüger Claus Lämmerzahl Alberto Lobo Xinlian Luo Helen Margolis Wei-Tou Ni Antonio Pulido Patón Qiuhe Peng Achim Peters Ernst Rasel Albrecht Rüdiger Étienne Samain Hanns Selig Diana Shaul Timothy Sumner Stephan Theil Pierre Touboul Slava Turyshev Haitao Wang Li Wang Linqing Wen Andreas Wicht Ji Wu Xiaomin Zhang Cheng Zhao 《Experimental Astronomy》2009,23(2):491-527
ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with
an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development
of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and
our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude
improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an
international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD
missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way,
two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth,
to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would
test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense–Thirring effect to 10 ppm, and
probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger
orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below
the ASTROD II bandwidth.
相似文献
Wei-Tou NiEmail: |
248.
Raymond Asare Tutu John Kwame Boateng Janice Desire Busingye Edmund Ameyaw 《GeoJournal》2017,82(5):907-921
This exploratory study examines how migrants’ lifestyles are associated with subjective assessment of their health status in a relatively poor urban neighborhood in Accra. For more than half a century, urban centers have been on the receiving end of internal migrants in Ghana with Accra, Kumasi, and Sekondi-Takoradi receiving the lion’s share. However, a lot of migrants end up in poor neighborhoods due to inability to afford relatively costly rents in the better residential areas in the cities. Migrants who live on the margins of society are adversely impacted by poor environmental conditions that make them susceptible to environmentally-induced diseases such as malaria, cholera, and typhoid. While the poverty, health, and place research in Accra, Ghana, have focused on spatial distribution of inequalities in health, burden of sexual ill health, double burden of diseases, environment, wealth and health relationship, as well as income and health connections, there is paucity of research on association between the daily lifestyles of migrants in poor urban neighborhoods and their health status. Specifically on lifestyle and contextual factors, we examine (1) eating and drinking behavior, (2) perception of environmental factors, (3) attitudes and practices during illnesses, and (4) physical activities. Results from Ordinal Logit Regression models suggest that the key predictors of self-rated health status are: (1) socio-demographic elements like length of stay, job type, and religiosity; and (2) eating and drinking behavior—frequency of buying food from food vendors, and (3) social capital. 相似文献
249.
Raymond A. Duraiswami Vrishali Dumale Usha Shetty 《Journal of the Geological Society of India》2009,73(5):621-638
Runoff has increased many fold in urban areas due to increase in paved areas, training of streams and construction of storm
water drains. The recharge is therefore continuously decreasing; resulting in depleting groundwater reserves beneath large
cities, especially those situated on water divides. In order to reduce surface runoff and replenish groundwater many advocate
artificial recharge through rainwater harvesting. Conventionally, detailed hydrogeological survey is needed by expert hydrogeologists
to suggest suitable sites for rooftop rainwater harvesting and storage in the subsurface aquifers. Pune, a rapidly growing
city, is under severe stress due to shortage of water in some areas. An effort has been made in this study to identify areas
suitable for rooftop rainwater harvesting by integrating traditional hydrogeological survey data with the help of Remote Sensing
and Geographic Information System. This endeavour has led to develop a program called SLUGGER-DQL which helps to identify
potential sites for rooftop rainwater harvesting and artificial recharge. The program is open ended and several other factors
controlling potential recharge can be easily added on. Based on the results of the present study, potential sites for rainwater
harvesting and artificial recharge have been identified in the Pune University-Shivajinagar-Kothrud area. The present paper
demonstrates the utility of traditional hydrogeological surveys combined with modern techniques in solving problems related
to urban hydrogeology and town planning. 相似文献
250.
Quantitative assessment of precipitation seasonality and summer surface wetness using ombrotrophic sediments from an Arctic Norwegian peatland 总被引:1,自引:0,他引:1
Jonathan E. Nichols Marie Walcott Raymond Bradley Jon Pilcher Yongsong Huang 《Quaternary Research》2009,72(3):443-451
Seasonality of precipitation is an important yet elusive climate parameter in paleoclimatological reconstructions. This parameter can be inferred qualitatively from pollen and other paleoecological methods, but is difficult to assess quantitatively. Here, we have assessed seasonality of precipitation and summer surface wetness using compound specific hydrogen and carbon isotope ratios of vascular plant leaf waxes and Sphagnum biomarkers extracted from the sediments of an ombrotrophic peatland, Bøstad Bog, Nordland, Norway. Our reconstructed precipitation seasonality and surface wetness are consistent with regional vegetation reconstructions. During the early Holocene, 11.5–7.5 ka, Fennoscandia experienced a cool, moist climate. The middle Holocene, 7.5–5.5 ka, was warm and dry, transitioning towards cooler and wetter conditions from the mid-Holocene to the present. Changes in seasonality of precipitation during the Holocene show significant coherence with changes in sea surface temperature in the Norwegian Sea, with higher SST corresponding to greater percentage of winter precipitation. Both high SST in the Norwegian Sea and increased moisture delivery to northern Europe during winter are correlated with a strong gradient between the subpolar low and subtropical high over the North Atlantic (positive North Atlantic Oscillation). 相似文献