全文获取类型
收费全文 | 241篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
大气科学 | 44篇 |
地球物理 | 29篇 |
地质学 | 121篇 |
海洋学 | 15篇 |
天文学 | 22篇 |
自然地理 | 15篇 |
出版年
2024年 | 1篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 6篇 |
2013年 | 18篇 |
2012年 | 10篇 |
2011年 | 14篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 15篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1991年 | 3篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 46 毫秒
91.
Transient creep of the lithosphere and its role in geodynamics 总被引:1,自引:0,他引:1
B. I. Birger 《Izvestiya Physics of the Solid Earth》2012,48(6):496-503
Laboratory experiments with samples of rocks show that at small strains there is transient creep, at which the strain grows with time, and the strain rate decreases. Plate tectonics allows only small strains in the lithospheric plates, so that the lithosphere creep is transient. In geodynamics, the lithosphere is regarded as a cold boundary layer formed by mantle convection. If we assume that the lithosphere has a steady-state creep, which is described by power-law non-Newtonian rheological model, the low effective viscosity of the lower layers of the lithosphere, obtained by data on small-scale postglacial flows, is possible only at high strain rates in these layers. However, the high strain rates in the lithosphere induce large strains that contradict plate tectonics. Transient creep of the lithosphere leads to its mobility at small strains, removing the discrepancy between thermal convection in the mantle and plate tectonics, which holds in the case of power-law rheological model of the lithosphere. 相似文献
92.
Ulf Helldn 《Global and Planetary Change》2008,64(3-4):158
This paper presents the development of a system dynamic model to simulate and analyze desertification.The human–environment coupled model integrates socio-economic drivers with bio-physical drivers of biomass production, land degradation and desertification. It is based on the UN and GEF definitions of desertification. It illustrates the concept of desertification through differential equation and simulation output graphics. It is supplemented with a causal loop diagram demonstrating the existing feed-back mechanisms.The model relates population pressure and dynamics over time to the growth and availability of biomass resources. The human population stock is described as a function of growth rate, death rate and resources dependent in and out migration of people. The relative growth rate of the stock of resources is modeled as a function of climate and exploitation pressure affecting soil erosion and water availability.The model is applied for the Sahelian desertification syndrome using input data to illustrate and simulate a 150 years period (1900–2050) in Kordofan, Sudan. The model indicates that it is difficult to generate irreversible desertification. 相似文献
93.
Abstract. Sediment parameters (grain size, organic content, chloroplastic pigments, Adenylates, Potential hydrolytic activity and electron transport system activity) and benthic biota were studied in methane seep area south-west of the Crimean Peninsula in the Black Sea over a depth range from 60 to 260m. A control transect with similar depths was performed in an adjacent nonseep area. Methane seepage in this region occurs from 35 to ˜ 85m depth, passing the oxic anoxic interface zone at 130 to 180m. The methane seep areas were characterized by abundant carbonate precipitates which occurred in various shapes from small, flat structures to tall chimneys with increasing anoxia. The carbonates were associated with distinct bacterial mats. Most of the measured biochemical parameters in the sediment were quite similar in the seep and nonseep areas. The content of organic matter was higher and grain size was more uniform in the nonseep areas. However, the seep areas were charaterized by highter proportions of the larger fauna (size classes 0.5–1 mm and ≥ 1mm) as well as increased total numbers of benthic fauna in the suboxic and upper anoxic zone. The animals did not show any seep-specific adaptations. In addition to methane seepage, highly variable hydrochemical and sedimentary conditions on the lower shelf and upper slope may also play an important role in structuring the composition and distribution of the benthic fauna. 相似文献
94.
Theory And Measurements For Turbulence Spectra And Variances In The Atmospheric Neutral Surface Layer 总被引:3,自引:17,他引:3
Predictions from a new theory for high Reynolds number turbulent boundary layers during near-neutral conditions are shown to agree well with measurements of atmospheric surface-layer variances and spectra. The theory suggests surface-layer turbulence is determined by detached eddies that largely originate in the shearing motion immediately above the surface layer; as they descend into this layer, they are strongly distorted by the local shear and impinge onto the surface. Because the origin of these eddies is non-local, they are similar to those described in previous studies as `inactive' turbulence. However, they are, in fact, dynamically highly active, supplying the major mechanism for the momentum transport, including upward bursting on the time scale of the larger eddies. The vertical velocity results show that the variance and the low frequency parts of spectra increase with height in the surface layer, while in the self similar (k1
-1) range the streamwise low frequency components are approximately constant with height. These large-scale longitudinal eddies extend to a length s, which is equal to the boundary-layer height near the surface andincreases linearly to a maximum of about three times the boundary-layer height at roughly 15 m and decreases in the upper parts of the surface layer. This lower part of the surface layer, the eddy surface layer, is the region in which the eddies impinging from layers above are strongly distorted. This new result for the atmospheric boundary layer has practical application for calculating fluctuating wind loads on structures and lateral dispersion of pollution from local sources. 相似文献
95.
Ann-Sofi Smedman Sven-Erik Gryning Karl Bumke Ulf H gstr m Anna Rutgersson Ekaterina Batchvarova Gerhard Peters Barbara Hennemuth Bengt Tammelin Reijo Hyv nen Anders Omstedt Daniel Michelson Tage Andersson Marco Clemens 《Journal of Atmospheric & Ocean Science》2005,10(3):163-191
Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project called PEP in BALTEX (Pilot study of Evaporation and Precipitation in the Baltic Sea), combining extensive field measurements and modelling efforts. Eddy-correlation-measurements of turbulent heat flux were made on a semi-continuous basis for a 12 month period at four well-exposed coastal sites in the Baltic Proper (the main basin of the Baltic Sea). Precipitation was measured at land-based sites with standard gauges and on four merchant ships travelling between Germany and Finland with the aid of specially designed ship rain gauges (SRGs). The evaporation and precipitation regime of the Baltic Sea was modelled for a 12 month period by applying a wide range of numerical models: the operational atmospheric High Resolution Limited Area Model (HIRLAM, Swedish and Finnish versions), the German atmospheric REgional-scale MOdel, REMO, the operational German Europe Model (only precipitation), the oceanographic model PROBE-Baltic, and two models that use interpolation of ground-based data, the Swedish MESAN model of SMHI and a German model of IFM-GEOMAR Kiel. Modelled precipitation was compared with SRG measurements on board the ships. A reasonable correlation was obtained, but the regional-scale models and MESAN gave some 20% higher precipitation over the sea than is measured. Bulk parameterisation schemes for evaporation were evaluated against measurements. A constant value of CHN and CEN with wind speed, underestimated large fluxes of both sensible and latent heat flux. The limited area models do not resolve the influence of the height of the marine boundary layer in coastal zones and the entrainment (on the surface fluxes), which may explain the observed low correlations between modelled and measured latent heat fluxes. Estimates of evaporation, E, and precipitation, P, for the entire Baltic Proper were made with several models for a 12 month period. While the annual variation was well represented by all predictions, there are still important differences in the annual means. Evaporation ranges from 509 to 625 mm year-1 and precipitation between 624 and 805 mm year-1 for this particular 12 month period. Taking the results of model verification from the present study into account, the best estimate of P-E is about 100 ± 50 mm for this particular 12 month period. But the annual mean of P-E varies considerably from year to year. This is reflected in simulations with the PROBE-Baltic model for an 18 year period, which gave 95 mm year-1 for the 12 month period studied here and 32 mm year-1 as an average for 18 years. 相似文献
96.
Birger Rasmussen Andreas G. Mueller Ian R. Fletcher 《Contributions to Mineralogy and Petrology》2009,157(5):559-572
In situ SHRIMP U–Pb dating of magmatic zirconolite (CaZrTi2O7) in the Golden Mile Dolerite from the Mt Charlotte gold deposit (Yilgarn Craton, Australia) has yielded the first robust
emplacement age (2,680 ± 9 Ma) for the principle host-rock of gold mineralization in the Kalgoorlie district. In contrast,
co-magmatic zircon gave ages from ~2.68 Ga to ~2.17 Ga, reflecting isotopic resetting of high-U and -Th crystals. In situ
SHRIMP analysis of hydrothermal xenotime (YPO4), which co-exists with gold in alteration pyrite, provided a Pb/Pb isochron age of 2,655 ± 13 Ma. This date indicates that
the youngest deposit in the Kalgoorlie district (Mt Charlotte) formed at ~2.65 Ga, and provides a new minimum age for the
structurally older Golden Mile deposit. Our results indicate that gold mineralization at Mt Charlotte is ~50 million years
older than indicated by recent 40Ar/39Ar dating and places new constraints on the timing of late-stage regional faulting (D4) in the province. 相似文献
97.
Birger Hansen 《Contributions to Mineralogy and Petrology》1981,76(2):234-242
The pressure-temperature curve for the equilibrium anorthite+2enstatite=pyrope+diopside+quartz has been determined in the system CaO-MgO-Al2O2-SiO2 to be between 13.4 and 14.0 kbars at 900° C. The slope up to 1,240° C is 8.5 bar/K. The entropy change at 1,200 K is 20 kJ. These data, combined with data from the literature, lead to a geobarometer equation which, when applied to rocks from the Agto area (West Greenland), gives pressure estimates of 6–10 kbars at 800° C. The results are consistent for rocks of differing Fe/Mg ratios and are consistent with independent pressure estimates. 相似文献
98.
A flow-foliated felsic ignimbrite constitutes the uppermost lithological unit of the 1.58 Gyr anorogenic magmatic rocks in SW Finland. The ignimbrite is derived from an explosive eruption of hot (≅ 950 °C) phenocryst-bearing A-type (rapakivi-type granite magma.
The ignimbrite is close in composition to subvolcanic rapakivi granites that occur in the margins of the kand rapakivi batholith. The subvolcanic granites crystallized under a pressure of ≅ 1 kbar and at temperatures of about 650–700 °C. However, both major and rare earth elements show that the ignimbrite- forming magma was more fractionated than the magma forming the subvolcanic varieties.
Supported by evidence of mafic-felsic magma mingling, it is suggested that injection of hot mafic magma into a shallow magma chamber produced the high temperature of the ignimbrite-forming magma. This injection increased the magmatic and the volatile pressure that caused the eruption of the dry felsic magma. 相似文献
The ignimbrite is close in composition to subvolcanic rapakivi granites that occur in the margins of the kand rapakivi batholith. The subvolcanic granites crystallized under a pressure of ≅ 1 kbar and at temperatures of about 650–700 °C. However, both major and rare earth elements show that the ignimbrite- forming magma was more fractionated than the magma forming the subvolcanic varieties.
Supported by evidence of mafic-felsic magma mingling, it is suggested that injection of hot mafic magma into a shallow magma chamber produced the high temperature of the ignimbrite-forming magma. This injection increased the magmatic and the volatile pressure that caused the eruption of the dry felsic magma. 相似文献
99.
Constraining a SHRIMP U-Pb age: micro-scale characterization of zircons from Saxonian Rotliegend rhyolites 总被引:7,自引:0,他引:7
Lutz Nasdala Jens Götze Robert T. Pidgeon Ulf Kempe Thomas Seifert 《Contributions to Mineralogy and Petrology》1998,132(3):300-306
We present results of a detailed investigation of zircons from two rhyolites from St. Egidien and Chemnitz, Saxony, using
a combination of microprobe techniques (SHRIMP ion probe, Raman microprobe, SEM: SE, BSE, and CL imaging). These rhyolites
belong to the so-called “lower volcanics”, which is the older of two series of Late Variscan volcanic rocks occurring in the
Saxonian Sub-Erzgebirge basin (Germany). The purpose of the present contribution is to demonstrate that detailed characterization
of zircons, as provided by the different micro-techniques, facilitates soundest interpretation of geochronological data. The
zircons (at most 40 to 80 m in size) show oscillatory growth zoning, with reversely correlated CL and BSE signal intensities. These zircons are interpreted
to have grown during crystallization of the rhyolite because, apart from some cracking, they do not appear to have experienced
any alteration since the time of their growth: The shapes of the zircons and their internal structures revealed by CL and
BSE imaging appear to be magmatic, and neither annealing of the accumulated alpha-decay damage nor disturbance of the U-Pb
system is observed. The SHRIMP ion probe measurements on the zircons gave a Permian 206Pb/238U age of 278 ± 5 Ma (95% confidence). The concordance of this age is supported by the correlation between the low degrees
of metamictization (estimated from Raman parameters) and the accumulated alpha fluxes (calculated from SHRIMP data). The 278
Ma zircon age is interpreted to represent the age of the “lower rhyolites” series and, with that, the age of postkinematic
Late Variscan volcanism in the Sub-Erzgebirge basin, which has been related to anorogenic extension and uplift as a result
of intracontinental rifting. Because of genetic association of rhyolites in the Sub-Erzgebirge basin and Li-F granites and
lamprophyres in the neighbouring Erzgebirge, the rhyolite age also indirectly contributes to the understanding of the geological
history of the Erzgebirge. The 278 Ma age is the first absolute dating result for rhyolites from the Saxonian Sub-Erzgebirge
basin.
Received: 16 December 1997 / Accepted: 4 May 1998 相似文献
100.