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811.
Somali Jet changes will influence the variability of Asian monsoon and climate. How would Somali Jet changes respond to the global warming in the future climate? To address this question, we first evaluate the ability of IPCC-AR4 climate models and perform the 20th century climate in coupled models (20C3M) experiments to reproduce the observational features of the low level Somali Jet in JJA (June-July-August) for the period 1976 1999. Then, we project and discuss the changes of Somali Jet under the climate change of Scenario A2 (SRESA2) for the period 2005 2099. The results show that 18 IPCC-AR4 models have performed better in describing the climatological features of Somali Jet in the present climate simulations. Analysis of Somali Jet intensity changes from the multi-model ensemble results for the period 2005-2099 shows a weakened Somali Jet in the early 21st century (2010-2040), the strongest Somali Jet in the middle 21st century (2050 2060), as well as the weakest Somali Jet at the end of the 21st century (2070-2090). Compared with the period 1976-1999, the intensity of Somali Jet is weakening in general, and it becomes the weakest at the end of the 21st century. The results also suggest that the relationship between the intensity of Somali Jet in JJA and the increment of global mean surface air temperature is nonlinear, which is reflected differently among the models, suggesting the uncertainty of the IPCC-AR4 models. Considering the important role of Somali Jet in the Indian monsoon and East Asian monsoon and climate of China, the variability of Somali Jet and its evolvement under the present climate or future climate changes need to be further clarified. 相似文献
812.
Simulations of subtropical marine low clouds and their radiative properties by nine coupled ocean-atmosphere climate models
participating in the fourth assesment report (AR4) of the intergovernmental panel on climate change (IPCC) are analyzed. Satellite
observations of cloudiness and radiative fluxes at the top of the atmosphere (TOA) are utilized for comparison. The analysis
is confined to the marine subtropics in an attempt to isolate low cloudiness from tropical convective systems. All analyzed
models have a negative bias in the low cloud fraction (model mean bias of −15%). On the other hand, the models show an excess
of cloud radiative cooling in the region (model mean excess of 13 W m−2). The latter bias is shown to mainly originate from too much shortwave reflection by the models clouds rather than biases
in the clear-sky fluxes. These results confirm earlier studies, thus no major progress in simulating the marine subtropical
clouds is noted. As a consequence of the combination of these two biases, this study suggests that all investigated models
are likely to overestimate the radiative response to changes in low level subtropical cloudiness. 相似文献
813.
Mechanisms for the land/sea warming contrast exhibited by simulations of climate change 总被引:3,自引:3,他引:0
Manoj M. Joshi Jonathan M. Gregory Mark J. Webb David M. H. Sexton Tim C. Johns 《Climate Dynamics》2008,30(5):455-465
The land/sea warming contrast is a phenomenon of both equilibrium and transient simulations of climate change: large areas
of the land surface at most latitudes undergo temperature changes whose amplitude is more than those of the surrounding oceans.
Using idealised GCM experiments with perturbed SSTs, we show that the land/sea contrast in equilibrium simulations is associated
with local feedbacks and the hydrological cycle over land, rather than with externally imposed radiative forcing. This mechanism
also explains a large component of the land/sea contrast in transient simulations as well. We propose a conceptual model with
three elements: (1) there is a spatially variable level in the lower troposphere at which temperature change is the same over
land and sea; (2) the dependence of lapse rate on moisture and temperature causes different changes in lapse rate upon warming
over land and sea, and hence a surface land/sea temperature contrast; (3) moisture convergence over land predominantly takes
place at levels significantly colder than the surface; wherever moisture supply over land is limited, the increase of evaporation
over land upon warming is limited, reducing the relative humidity in the boundary layer over land, and hence also enhancing
the land/sea contrast. The non-linearity of the Clausius–Clapeyron relationship of saturation specific humidity to temperature
is critical in (2) and (3). We examine the sensitivity of the land/sea contrast to model representations of different physical
processes using a large ensemble of climate model integrations with perturbed parameters, and find that it is most sensitive
to representation of large-scale cloud and stomatal closure. We discuss our results in the context of high-resolution and
Earth-system modelling of climate change. 相似文献
814.
S. Parey 《Climate Dynamics》2008,30(1):99-112
Power plant construction requires anticipation to achieve a liable dimensioning on the long functioning time of the installation.
In the present climate change context, dimensioning towards extremely high temperature for installations intended to run until
the 2070s or later implies an evaluation of plausible extreme values at this time scale. This study is devoted to such an
estimation for France, using both observation series and climate model simulation results. The climate model results are taken
from the European PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining European Climate change risks
and Effects) project database of regional climate change scenarios for Europe. Comparison of high summer temperature distributions
given by observations and climate models under current climate conditions, conducted using Generalized Extreme Value distribution,
reveals that only a few models are able to correctly reproduce it. For these models, climate change under IPCC A2 and B2 scenarios
leads to differences in the variability of high values, whose proportion has an important impact on future 100-year return
levels.
This study was first presented at the EGU General Assembly in Vienna, 2–7 April 2006. 相似文献
815.
The interest in the national levels of the terrestrial carbon sink and its spatial and temporal
variability with the climate and CO2 concentrations has been increasing. How the climate and the increasing
atmospheric CO2 concentrations in the last century affect the carbon storage in continental China was
investigated in this study by using the Modified Sheffield Dynamic Global Vegetation Model (M-SDGVM).
The estimates of the M-SDGVM indicated that during the past 100 years a combination of increasing CO2
with historical temperature and precipitation variability in continental China have caused the total
vegetation carbon storage to increase by 2.04 Pg C, with 2.07 Pg C gained in the vegetation biomass
but 0.03 Pg C lost from the organic soil carbon matter. The increasing CO2 concentration in the 20th
century is primarily responsible for the increase of the total potential vegetation carbon. These
factorial experiments show that temperature variability alone decreases the total carbon storage by
1.36 Pg C and precipitation variability alone causes a loss of 1.99 Pg C. The effect of the increasing
CO2 concentration alone increased the total carbon storage in the potential vegetation of China by
3.22 Pg C over the past 100 years. With the changing of the climate, the CO2 fertilization on China's
ecosystems is the result of the enhanced net biome production (NBP), which is caused by a greater
stimulation of the gross primary production (GPP) than the total soil-vegetation respiration. Our study
also shows notable interannual and decadal variations in the net carbon exchange between the atmosphere
and terrestrial ecosystems in China due to the historical climate variability. 相似文献
816.
The Central India Tectonic Zone (CITZ) is a prominent divide and a major suture zone between the North Indian and South Indian crustal blocks. The resistive upper crust as modeled in the magnetotelluric data from CITZ suggests a dominant tonalite–trdondhjemite–granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components. The highly conductive bodies in this zone might represent mafic/ultramafic-layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the Cretaceous Deccan flood basalts. The uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of Archaean and Paleoproterozoic subducted slabs. We redefine the nature of deep faults traversing the CITZ, which were described as steep and penetrating the Moho by previous workers, and classify them as listric faults with gentle dips at depth.Seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the Bhandara Craton. Reflection data from the central part of the CITZ show northerly dip in the southern part suggesting northward subduction of the Dharwar Craton. However, an opposite trend is observed in the northern part of the suture with a southward dip of the Bundelkhand craton. Based on these features, and in conjunction with existing magnetotelluric models, we propose a double-sided subduction history along the CITZ. This would be similar to the ongoing subduction–accretion process in the western Pacific region, which possibly led to the development of paired collision-type and Pacific-type orogens. One important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust. The high resistivity felsic domain suggests underplated sediments/felsic crust that would have caused the doming. Our model also accounts for the extrusion of regional metamorphic belts at the orogenic core, and the occurrence of high pressure–ultrahigh-temperature paired metamorphic belts within the suture. 相似文献
817.
818.
In the British and Irish Isles, the understanding of expansion and retreat of the last ice sheet in Marine Isotope Stage (MIS) 2 has been hindered by a lack of chronological control for the timing of its maximum extent and subsequent retreat stages. In this research, a suite of lithofacies from a former distal ice marginal sandur at Orrisdale, Isle of Man, were identified and selected for optically stimulated luminescence dating. Different‐size fractions of quartz grains were extracted from selected lithofacies types with the aim of identifying which depositional environments and grain size fractions are best suited for optical dating. Tests have been undertaken to identify the luminescence properties of this quartz, including preheat dose recovery and constant‐wave optically stimulated luminescence (OSL) decay curve fitting. Equivalent dose distributions for all samples were wide and positively skewed, indicative of heterogeneous bleaching. A comprehensive statistically based decision‐making protocol has been defined in order to find the appropriate statistical model for burial dose estimation. Ages in the range of 17–14 ka have been obtained which agree with the expected geologically constrained chronology. The Orrisdale Formation is contemporaneous with Heinrich Event 1 and the Killard Point Stadial identified in eastern Ireland ca. 16.4 ka. The suggested approach for OSL dating of glaciofluvial sediments has the potential for much wider application to high latitude or temperate areas where there is an abundance of such sediments and where improved chronological control is much needed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
819.
820.
Cosmology with the gravitational and cosmological constants generalized as coupling scalars in Einsteins theory is considered.
A general method of solving the field equations is given. Exact solution for Zeldovich fluid satisfying G=G
0(R/R
0)
n
is given. 相似文献