全文获取类型
收费全文 | 1089篇 |
免费 | 56篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 188篇 |
地球物理 | 260篇 |
地质学 | 455篇 |
海洋学 | 36篇 |
天文学 | 123篇 |
综合类 | 6篇 |
自然地理 | 58篇 |
出版年
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 26篇 |
2020年 | 27篇 |
2019年 | 25篇 |
2018年 | 38篇 |
2017年 | 30篇 |
2016年 | 60篇 |
2015年 | 46篇 |
2014年 | 61篇 |
2013年 | 79篇 |
2012年 | 62篇 |
2011年 | 75篇 |
2010年 | 61篇 |
2009年 | 71篇 |
2008年 | 60篇 |
2007年 | 48篇 |
2006年 | 58篇 |
2005年 | 51篇 |
2004年 | 34篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 23篇 |
2000年 | 14篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1957年 | 2篇 |
1955年 | 1篇 |
1951年 | 1篇 |
1950年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有1156条查询结果,搜索用时 31 毫秒
961.
962.
Robert Andritschke Andreas Zoglauer Gottfried Kanbach Peter F. Bloser Florian Schopper 《Experimental Astronomy》2005,20(1-3):395-403
MEGA, short for Medium Energy Gamma-ray Astronomy, is the development of a new technology telescope in the energy band 0.4--50\ MeV. The wide energy range of MEGA, which spans nuclear γ-ray lines and energetic continuum spectra, the large field of view, and the capacity for polarimetry enables unique investigations into cosmic nucleosynthesis, particle accelerators around compact objects, and explosive high-energy events. We describe the development and tests of a prototype detector. Results from laboratory tests using radioactive sources and from a beam test calibration are presented and an outlook of a potential space mission is sketched. 相似文献
963.
964.
Wilbert Weijer Wilhelmus P. M. De Ruijter Andreas Sterl Sybren S. Drijfhout 《Global and Planetary Change》2002,34(3-4)
The heat and salt input from the Indian to Atlantic Oceans by Agulhas Leakage is found to influence the Atlantic overturning circulation in a low-resolution Ocean General Circulation Model (OGCM). The model used is the Hamburg Large-Scale Geostrophic (LSG) model, which is forced by mixed boundary conditions. Agulhas Leakage is parameterized by sources of heat and salt in the upper South Atlantic Ocean, which extend well into the intermediate layers.It is shown that the model's overturning circulation is sensitive to the applied sources of heat and salt. The response of the overturning strength to changes in the source amplitudes is mainly linear, interrupted once by a stepwise change. The South Atlantic buoyancy sources influence the Atlantic overturning strength by modifying the basin-scale meridional density and pressure gradients. The non-linear, stepwise response is caused by abrupt changes in the convective activity in the northern North Atlantic.Two additional experiments illustrate the adjustment of the overturning circulation upon sudden introduction of heat and salt sources in the South Atlantic. The North Atlantic overturning circulation responds within a few years after the sources are switched on. This is the time it takes for barotropic and baroclinic Kelvin waves to reach the northern North Atlantic in this model. The advection of the anomalies takes three decades to reach the northern North Atlantic.The model results give support to the hypothesis that the re-opening of the Agulhas Gap at the end of the last ice-age, as indicated by palaeoclimatological data, may have stimulated the coincident strengthening of the Atlantic overturning circulation. 相似文献
965.
966.
We compare results from numerical simulations with observations of edge-on galaxies interacting/merging with a small companion
(Schwarzkopf and Dettmar,2000), hereafter S&D00). Observations show a clear influence of the merging and interacting process
on disk scale parameters h (radial scalelength), z
0 (vertical scalelength) and their ratio (h/z
0), leading to a heating and thickening of the stellar disk. Our numerical simulations show the same behaviour but differ significantly
in the magnitude of the change of the disk scale parameters.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
967.
968.
Sebastian Tappe Stephen F. Foley Rolf L. Romer Andreas Stracke 《Geochimica et cosmochimica acta》2008,72(13):3258-3286
New U-Pb perovskite ages reveal that diamondiferous ultramafic lamprophyre magmas erupted through the Archean crust of northern Labrador and Quebec (eastern Canada) between ca. 610 and 565 Ma, a period of strong rifting activity throughout contiguous Laurentia and Baltica. The observed Torngat carbonate-rich aillikite/carbonatite and carbonate-poor mela-aillikite dyke varieties show a large spread in Sr-Nd-Hf-Pb isotope ratios with pronounced correlations between isotope systems. An isotopically depleted component is identified solely within aillikites (87Sr/86Sri = 0.70323-0.70377; εNdi = +1.2-+1.8; εHfi = +1.4-+3.5; 206Pb/204Pbi = 18.2-18.5), whereas some aillikites and all mela-aillikites range to more enriched isotope signatures (87Sr/86Sri = 0.70388-0.70523; εNdi = −0.5 to −3.9; εHfi = −0.6 to −6.0; 206Pb/204Pbi = 17.8-18.2). These contrasting isotopic characteristics of aillikites/carbonatites and mela-aillikites, along with subtle differences in their modal carbonate, SiO2, Al2O3, Na2O, Cs-Rb, and Zr-Hf contents, are consistent with two distinctive metasomatic assemblages of different age in the mantle magma source region.Integration of petrologic, geochemical, and isotopic information leads us to propose that the isotopically enriched component originated from a reduced phlogopite-richterite-Ti-oxide dominated source assemblage that is reminiscent of MARID suite xenoliths. In contrast, the isotopically depleted component was derived from a more oxidized phlogopite-carbonate dominated source assemblage. We argue that low-degree CO2-rich potassic silicate melts from the convective upper mantle were preferentially channelled into an older, pre-existing MARID-type vein network at the base of the North Atlantic craton lithosphere, where they froze to form new phlogopite-carbonate dominated veins. Continued stretching and thinning of the cratonic lithosphere during the Late Neoproterozoic remobilized the carbonate-rich vein material and induced volatile-fluxed fusion of the MARID-type veins and the cold peridotite substrate. Isotopic modelling suggests that only 5-12% trace element contribution from such geochemically extreme MARID-type material is required to produce the observed compositional shift from the isotopically most depleted aillikites/carbonatites towards enriched mela-aillikites.We conclude that cold cratonic mantle lithosphere can host several generations of contrasting vein assemblages, and that each may have formed during past tectonic and magmatic events under distinctively different physicochemical conditions. Although cratonic MARID-type and carbonate-bearing veins in peridotite can be the respective sources for lamproite and carbonatite magmas when present as the sole metasome, their concomitant fusion in a complex source region may give rise to a whole new variety of deep volatile-rich magmas and we suggest that orangeites (formerly Group 2 kimberlites), kamafugites, and certain types of ultramafic lamprophyre are formed in this manner. 相似文献
969.
The integration of distributed geospatial data is a great issue in GI Science. Hereby, the collection of data from different systems and different structures as well as across country borders is a problem. We explain a model‐based four‐step approach to conceptual data modelling. Within this approach, we introduce a methodology to map data models on the conceptual level without touching data formats. First, we developed a conceptual mapping language called “UMLT” which is the core of our approach. Furthermore, we integrated UMLT into the Model‐Driven Architecture where a conceptual model mapping is referred to as a platform independent model mapping. Finally, the data format transformation is deduced from the model mapping automatically. This represents the implementation mapping from a platform independent model to a platform specific model. Together with transformation operations for attribute mapping, this approach is a means for effective and enhanced semantic interoperability. 相似文献
970.
Impact of Neutral Boundary-Layer Turbulence on Wind-Turbine Wakes: A Numerical Modelling Study 总被引:1,自引:1,他引:0
The wake characteristics of a wind turbine in a turbulent boundary layer under neutral stratification are investigated systematically by means of large-eddy simulations. A methodology to maintain the turbulence of the background flow for simulations with open horizontal boundaries, without the necessity of the permanent import of turbulence data from a precursor simulation, was implemented in the geophysical flow solver EULAG. These requirements are fulfilled by applying the spectral energy distribution of a neutral boundary layer in the wind-turbine simulations. A detailed analysis of the wake response towards different turbulence levels of the background flow results in a more rapid recovery of the wake for a higher level of turbulence. A modified version of the Rankine–Froude actuator disc model and the blade element momentum method are tested as wind-turbine parametrizations resulting in a strong dependence of the near-wake wind field on the parametrization, whereas the far-wake flow is fairly insensitive to it. The wake characteristics are influenced by the two considered airfoils in the blade element momentum method up to a streamwise distance of 14D (D = rotor diameter). In addition, the swirl induced by the rotation has an impact on the velocity field of the wind turbine even in the far wake. Further, a wake response study reveals a considerable effect of different subgrid-scale closure models on the streamwise turbulent intensity. 相似文献