全文获取类型
收费全文 | 524篇 |
免费 | 31篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 36篇 |
大气科学 | 44篇 |
地球物理 | 155篇 |
地质学 | 165篇 |
海洋学 | 31篇 |
天文学 | 85篇 |
综合类 | 2篇 |
自然地理 | 40篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 26篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 32篇 |
2012年 | 20篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 31篇 |
2008年 | 25篇 |
2007年 | 27篇 |
2006年 | 30篇 |
2005年 | 18篇 |
2004年 | 19篇 |
2003年 | 8篇 |
2002年 | 19篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1971年 | 4篇 |
1967年 | 3篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1963年 | 3篇 |
1962年 | 3篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有558条查询结果,搜索用时 15 毫秒
71.
72.
We describe a forward-fitting method that has been developed to reconstruct hard X-ray images of solar flares from the Ramaty
High-Energy Solar Spectroscopic Imager (RHESSI), a Fourier imager with rotation-modulated collimators that was launched on
5 February 2002. The forward-fitting method is based on geometric models that represent a spatial map by a superposition of
multiple source structures, which are quantified by circular gaussians (4 parameters per source), elliptical gaussians (6
parameters), or curved ellipticals (7 parameters), designed to characterize real solar flare hard X-ray maps with a minimum
number of geometric elements. We describe and demonstrate the use of the forward-fitting algorithm. We perform some 500 simulations
of rotation-modulated time profiles of the 9 RHESSI detectors, based on single and multiple source structures, and perform
their image reconstruction. We quantify the fidelity of the image reconstruction, as function of photon statistics, and the
accuracy of retrieved source positions, widths, and fluxes. We outline applications for which the forward-fitting code is
most suitable, such as measurements of the energy-dependent altitude of energy loss near the limb, or footpoint separation
during flares.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022469811115 相似文献
73.
The sensitivity of the North Atlantic gyre circulation to high latitude buoyancy forcing is explored in a global, non-eddy resolving ocean general circulation model. Increased buoyancy forcing strengthens the deep western boundary current, the northern recirculation gyre, and the North Atlantic Current, which leads to a more realistic Gulf Stream path. High latitude density fluxes and surface water mass transformation are strongly dependent on the choice of sea ice and salinity restoring boundary conditions. Coupling the ocean model to a prognostic sea ice model results in much greater buoyancy loss in the Labrador Sea compared to simulations in which the ocean is forced by prescribed sea ice boundary conditions. A comparison of bulk flux forced hindcast simulations which differ only in their sea ice and salinity restoring forcings reveals the effects of a mixed thermohaline boundary condition transport feedback whereby small, positive temperature and salinity anomalies in subpolar regions are amplified when the gyre spins up as a result of increased buoyancy loss and convection. The primary buoyancy flux effects of the sea ice which cause the simulations to diverge are ice melt, which is less physical in the diagnostic sea ice model, and insulation of the ocean, which is less physical with the prognostic sea ice model. Increased salinity restoring ensures a more realistic net winter buoyancy loss in the Labrador Sea, but it is found that improvements in the Gulf Stream simulation can only be achieved with the excessive buoyancy loss associated with weak salinity restoring. 相似文献
74.
The recent detection of very-high-energy (GeV – TeV) γ-ray emission from the Galactic black-hole candidate and microquasar LS 5039 has sparked renewed interest in jet models for
the high-energy emission in those objects. In this work, we have focused on models in which the high-energy emission results
from synchrotron and Compton emission by relativistic electrons in the jet (leptonic jet models). Particular attention has
been paid to a possible orbital modulation of the high-energy emission due to azimuthal asymmetries caused by the presence
of the companion star. Both orbital-phase dependentγγ absorption and Compton scattering of optical/UV photons from the companion star may lead to an orbital modulation of the
gamma-ray emission. We make specific predictions which should be testable with refined data from HESS and the upcoming GLAST
mission. 相似文献
75.
Markus Kissler-Patig 《Astrophysics and Space Science》2002,281(1-2):487-491
Old, metal-poor globular clusters trace the formation and evolution of early-type galaxies. Their are the best probes, at
low redshift, of the building-up of galaxy halos at high redshift. Their properties constrain the characteristics of their
progenitors. Recent results suggest that DLAs atz > 3 are the likely hosts for their formation. Finally, they shed light on the old, metal-poor halos probably present around
all early-type galaxies.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
76.
77.
Atmospheric boundary-layer structure observed during a haze event due to forest-fire smoke 总被引:1,自引:0,他引:1
Markus?PahlowEmail author Jan?Kleissl Marc?B.?Parlange 《Boundary-Layer Meteorology》2005,114(1):53-70
During a haze event in Baltimore, U.S.A. from July 6 to 8, 2002, smoke from forest fires in the Québec region (Canada), degraded air quality and impacted upon local climate, decreasing solar radiation and air temperature. The smoke particles in and above the atmospheric boundary layer (ABL) served as a tracer and provided a unique opportunity to investigate the ABL structure, especially entrainment. Elastic backscatter lidar measurements taken during the haze event distinctly reveal the downward sweeps (or wisps) of smoke-laden air from the free atmosphere into the ABL. Visualisations of mechanisms such as dry convection, the entrainment process, detrainment, coherent entrainment structures, and mixing inside the ABL, are presented. Thermals overshooting at the ABL top are shown to create disturbances in the form of gravity waves in the free atmosphere aloft, as evidenced by a corresponding ripple structure at the bottom of the smoke layer. Lidar data, aerosol ground-based measurements and supporting meteorological data are used to link free atmosphere, mixed-layer and ground-level aerosols. During the peak period of the haze event (July 7, 2002), the correlation between time series of elastic backscatter lidar data within the mixed layer and the scattering coefficient from a nephelometer at ground level was found to be high (R=0.96 for z =324 m, and R=0.89 for z=504 m). Ground-level aerosol concentration was at a maximum about 2 h after the smoke layer intersected with the growing ABL, confirming that the wisps do not initially reach the ground. 相似文献
78.
Wolfgang?StinnesbeckEmail author Gerta?Keller Thierry?Adatte Markus?Harting Doris?Stüben Georg?Istrate Utz?Kramar 《International Journal of Earth Sciences》2004,93(6):1042-1065
CSDP core Yaxcopoil-1 was drilled to a depth of 1,511 m within the Chicxulub crater. An organic-rich marly limestone near the base of the hole (1,495 to 1,452 m) was deposited in an open marine shelf environment during the latest Cenomanian (uppermost Rotalipora cushmani zone). The overlying sequence of limestones, dolomites and anhydrites (1,495 to 894 m) indicates deposition in various carbonate platform environments (e.g., sabkhas, lagoons). A 100-m-thick suevite breccia (894–794 m) identifies the Chicxulub impact event. Above the suevite breccia is a dolomitic limestone with planktic foraminiferal assemblages indicative of Plummerita hantkeninoides zone CF1, which spans the last 300 ky of the Maastrichtian. An erosional surface 50 cm above the breccia/dolomite contact marks the K/T boundary and a hiatus. Limestones above this contact contain the first Tertiary planktic foraminifera indicative of an upper P. eugubina zone P1a(2) age. Another hiatus 7 cm upsection separates zone P1a(2) and hemipelagic limestones of planktic foraminiferal Zone P1c. Planktic foraminiferal assemblages of Zone Plc to P3b age are present from a depth of 794.04 up to 775 m. The Cretaceous carbonate sequence appears to be autochthonous, with a stratigraphic sequence comparable to late Cretaceous sediments known from outside the Chicxulub crater in northern and southern Yucatan, including the late Cenomanian organic-rich marly limestone. There is no evidence that these sediments represent crater infill due to megablocks sliding into the crater, such as major disruption of sediments, chaotic changes in lithology, overturned or deep dipping megablocks, major mechanical fragmentation, shock or thermal alteration, or ductile deformation. Breccia units that are intercalated in the carbonate platform sequence are intraformational in origin (e.g., dissolution of evaporites) and dykes are rare. Major disturbances of strata by the impact therefore appear to have been confined to within less than 60 km from the proposed impact center. Yaxcopoil-1 may be located outside the collapsed transient crater cavity, either on the upper end of an elevated and tilted horst of the terrace zone, or even outside the annular crater cavity. The Chicxulub site thus records a large impact that predates the K/T boundary impact and mass extinction. 相似文献
79.
Momcilo Markus Donald J. Wuebbles Xin-Zhong Liang Katharine Hayhoe David A. R. Kristovich 《Climatic change》2012,111(3-4):879-902
Past heavy precipitation events in the Chicago metropolitan area have caused significant flood-related economic and environmental damages. A key component in flood management policies and actions is determining flood magnitudes for specified return periods. This is a particularly difficult task in areas with a complex and changing climate and land-use, such as the Chicago metropolitan area. The standard design storm methodology based on the NOAA Atlas 14 and ISWS Bulletin 70 has been used in the past to estimate flood hydrographs with variable return periods in this region. In a changing climate, however, these publications may not be accurate. This study presents and illustrates a methodology for diagnostic analysis of future climate scenarios in the framework of urban flooding, and assesses the corresponding uncertainties. First, the design storms are calculated using data downscaled by a regional climate model (RCM) at 30-km spacing for the present and 2050s under the IPCC A1Fi (high) and B1 (low) emissions scenarios. Next, the corresponding flood discharges at six watersheds in suburban Chicago are estimated using a hydrologic event model. The resulting scenarios in flood frequency were first assessed through a set of diagnostic tests for precipitation timing and frequency. The study did not reveal any significant changes in the 2050s in the average timing of heavy storms, but their regularity decreased. The average timing did not exhibit any significant spatial variability throughout the region. The precipitation frequency analysis revealed distinct differences between the northern and southeastern subregions of the Chicago metropolitan area. The quantiles in the northern subregion averaged for 2-year, 5-year, and 10-year return periods exhibited a 20% and 16% increase in daily precipitation for scenarios B1 and A1Fi, respectively. The southeastern subregion, however, exhibited a decrease of 12% for scenario B1 and a minor increase of 3% for scenario A1Fi. The hydrologic effects of changing precipitation on the flood quantiles were illustrated using six small watersheds in the region. The relative increases or decreases in precipitation translated into even larger relative increases or decreases in flood peaks, due to the nonlinear nature of the rainfall-runoff process. Simulations using multiple climate models, for longer periods, finer spatio-temporal resolution, and larger areal coverage could be used to more accurately account for numerous uncertainties in the precipitation and flood projections. 相似文献
80.
Ralf Döscher Klaus Wyser H. E. Markus Meier Minwei Qian René Redler 《Climate Dynamics》2010,34(7-8):1157-1176
The relative importance of regional processes inside the Arctic climate system and the large scale atmospheric circulation for Arctic interannual climate variability has been estimated with the help of a regional Arctic coupled ocean-ice-atmosphere model. The study focuses on sea ice and surface climate during the 1980s and 1990s. Simulations agree reasonably well with observations. Correlations between the winter North Atlantic Oscillation index and the summer Arctic sea ice thickness and summer sea ice extent are found. Spread of sea ice extent within an ensemble of model runs can be associated with a surface pressure gradient between the Nordic Seas and the Kara Sea. Trends in the sea ice thickness field are widely significant and can formally be attributed to large scale forcing outside the Arctic model domain. Concerning predictability, results indicate that the variability generated by the external forcing is more important in most regions than the internally generated variability. However, both are in the same order of magnitude. Local areas such as the Northern Greenland coast together with Fram Straits and parts of the Greenland Sea show a strong importance of internally generated variability, which is associated with wind direction variability due to interaction with atmospheric dynamics on the Greenland ice sheet. High predictability of sea ice extent is supported by north-easterly winds from the Arctic Ocean to Scandinavia. 相似文献