全文获取类型
收费全文 | 400篇 |
免费 | 17篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 37篇 |
地球物理 | 152篇 |
地质学 | 115篇 |
海洋学 | 40篇 |
天文学 | 50篇 |
自然地理 | 16篇 |
出版年
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 19篇 |
2015年 | 17篇 |
2014年 | 27篇 |
2013年 | 33篇 |
2012年 | 19篇 |
2011年 | 27篇 |
2010年 | 20篇 |
2009年 | 42篇 |
2008年 | 22篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 13篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1958年 | 3篇 |
1956年 | 2篇 |
1955年 | 3篇 |
1954年 | 1篇 |
1953年 | 2篇 |
1952年 | 2篇 |
1951年 | 3篇 |
1950年 | 3篇 |
1949年 | 1篇 |
1948年 | 1篇 |
1946年 | 2篇 |
1945年 | 1篇 |
1944年 | 3篇 |
排序方式: 共有422条查询结果,搜索用时 15 毫秒
41.
Tobias Lung Alessandro Dosio William Becker Carlo Lavalle Laurens M. Bouwer 《Climatic change》2013,120(1-2):211-227
Despite an increasing understanding of potential climate change impacts in Europe, the associated uncertainties remain a key challenge. In many impact studies, the assessment of uncertainties is underemphasised, or is not performed quantitatively. A key source of uncertainty is the variability of climate change projections across different regional climate models (RCMs) forced by different global circulation models (GCMs). This study builds upon an indicator-based NUTS-2 level assessment that quantified potential changes for three climate-related hazards: heat stress, river flood risk, and forest fire risk, based on five GCM/RCM combinations, and non-climatic factors. First, a sensitivity analysis is performed to determine the fractional contribution of each single input factor to the spatial variance of the hazard indicators, followed by an evaluation of uncertainties in terms of spread in hazard indicator values due to inter-model climate variability, with respect to (changes in) impacts for the period 2041–70. The results show that different GCM/RCM combinations lead to substantially varying impact indicators across all three hazards. Furthermore, a strong influence of inter-model variability on the spatial patterns of uncertainties is revealed. For instance, for river flood risk, uncertainties appear to be particularly high in the Mediterranean, whereas model agreement is higher for central Europe. The findings allow for a hazard-specific identification of areas with low vs. high model agreement (and thus confidence of projected impacts) within Europe, which is of key importance for decision makers when prioritising adaptation options. 相似文献
42.
Thresholds of hydrologic flow regime of a river and investigation of climate change impact—the case of the Lower Brahmaputra river Basin 总被引:1,自引:0,他引:1
The sustainability of social-ecological systems depends on river flows being maintained within a range to which those systems are adapted. In order to determine the extent of this natural range of variation, we assess ecological flow thresholds and the occurrence of potentially damaging flood events to society in the context of the Lower Brahmaputra river basin. The ecological flow threshold was calculated using twenty-two ‘Range of Variability (RVA)’ parameters, considering the range between?±?1 standard deviation from the mean of the natural flow. Damaging flood events were calculated using flood frequency analysis of Annual Maxima series and using the flood classification of Bangladesh. The climate change impacts on future river flow were calculated by using a weighted ensemble analysis of twelve global circulation models (GCMs) outputs driving a large-scale hydrologic model. The simulated climate change induced altered flow regime of the Lower Brahmaputra River Basin was then investigated and compared with the calculated threshold flows. The results demonstrate that various parameters including the monthly mean of low flow (January, February and March) and high flow (June, July and August) periods, the 7-day average minimum flow, and the yearly maximum flow will exceed the threshold conditions by 1956–1995 under the business-as-usual A1B and A2 future scenarios. The results have a number of policy level implications for government agencies of the Lower Brahmaputra River Basin, specifically for Bangladesh. The calculated thresholds may be used as a good basis for negotiations with other riparian countries of the basin. The methodological approach presented in this study can be applied to other river basins and provide a useful basis for transboundary water resources management. 相似文献
43.
GiuseppeCarloMarano 《地震工程与工程振动(英文版)》2005,4(1):95-106
Bridge seismic isolation strategy is based on the reduction of shear forces transmitted from the superstructure to the piers by two means: shifting natural period and earthquake input energy reduction by dissipation concentrated in protection devices. In this paper, a stochastic analysis of a simple isolated bridge model for different bridge and device parameters is conducted to assess the efficiency of this seismic protection strategy. To achieve this aim, a simple nonlinear softening constitutive law is adopted to model a wide range of isolation devices, characterized by only three essential mechanical parameters. As a consequence of the random nature of seismic motion, a probabilistic analysis is carried out and the time modulated Kanai-Tajimi stochastic process is adopted to represent the seismic action. The response covariance in the state space is obtained by solving the Lyapunov equation for a stochastic linearized system. After a sensitivity analysis, the failure probability referred to extreme displacement and the mean value of dissipated energy are assessed by using the introduced stochastic indices of seismic bridge protection efficiency. A parametric analysis for protective devices with different mechanical parameters is developed for a proper selection of parameters of isolation devices under different situations. 相似文献
44.
A Laser-induced Fluorescence Instrument for Detecting Tropospheric OH and HO2: Characteristics and Calibration 总被引:1,自引:0,他引:1
45.
Diffuse CO<Subscript>2</Subscript> degassing at Vesuvio,Italy 总被引:1,自引:0,他引:1
Francesco?FrondiniEmail author Giovanni?Chiodini Stefano?Caliro Carlo?Cardellini Domenico?Granieri Guido?Ventura 《Bulletin of Volcanology》2004,66(7):642-651
At Vesuvio, a significant fraction of the rising hydrothermal–volcanic fluids is subjected to a condensation and separation process producing a CO2–rich gas phase, mainly expulsed through soil diffuse degassing from well defined areas called diffuse degassing structures (DDS), and a liquid phase that flows towards the outer part of the volcanic cone. A large amount of thermal energy is associated with the steam condensation process and subsequent cooling of the liquid phase. The total amount of volcanic–hydrothermal CO2 discharged through diffuse degassing has been computed through a sequential Gaussian simulation (sGs) approach based on several hundred accumulation chamber measurements and, at the time of the survey, amounted to 151 t d–1. The steam associated with the CO2 output, computed assuming that the original H2O/CO2 ratio of hydrothermal fluids is preserved in fumarolic effluents, is 553 t d–1, and the energy produced by the steam condensation and cooling of the liquid phase is 1.47×1012 J d–1 (17 MW). The location of the CO2 and temperature anomalies show that most of the gas is discharged from the inner part of the crater and suggests that crater morphology and local stratigraphy exert strong control on CO2 degassing and subsurface steam condensation. The amounts of gas and energy released by Vesuvio are comparable to those released by other volcanic degassing areas of the world and their estimates, through periodic surveys of soil CO2 flux, can constitute a useful tool to monitor volcanic activity.Editorial responsibility: H. Shinohara 相似文献
46.
47.
Despite the growing concern about actual on-going climate change, there is little consensus on the scale and timing of actions needed to stabilise the concentrations of greenhouse gases. Many countries are unwilling to implement mitigation strategies, at least in the short term, and no agreement on an ambitious global stabilisation target has yet been reached. It is thus likely that international climate policies will be characterized by a high degree of uncertainty over the stringency of the climate objective, and that some countries might delay their participation to global action. What additional economic costs will this delay in the adoption of mitigation measures imply? What would the optimal short-term strategy be given the uncertainty surrounding the climate policy to come? Is there a hedging strategy that decision makers can adopt to cope with delayed action and uncertain targets? This paper addresses these questions by quantifying the economic implications of delaying mitigation action, and by computing the optimal abatement strategy in the presence of uncertainty about a global stabilisation target (which will be agreed upon in future climate negotiations). Results point to short-term inaction as the key determinant for the economic costs of ambitious climate policies. They also indicate that there is an effective hedging strategy that could minimise the cost of climate policy uncertainty over the global stabilisation target: a short-term moderate climate policy would be a good strategy to reduce the costs of delayed action and to cope with uncertainty about the outcome of future climate negotiations. By contrast, failing to curb emissions in the short term imposes rapidly increasing additional costs of compliance. 相似文献
48.
Till Kuhlbrodt Stefan Rahmstorf Kirsten Zickfeld Frode Bendiksen Vikebø Svein Sundby Matthias Hofmann Peter Michael Link Alberte Bondeau Wolfgang Cramer Carlo Jaeger 《Climatic change》2009,96(4):489-537
This paper discusses the risks of a shutdown of the thermohaline circulation (THC) for the climate system, for ecosystems
in and around the North Atlantic as well as for fisheries and agriculture by way of an Integrated Assessment. The climate
model simulations are based on greenhouse gas scenarios for the 21st century and beyond. A shutdown of the THC, complete by
2150, is triggered if increased freshwater input from inland ice melt or enhanced runoff is assumed. The shutdown retards
the greenhouse gas-induced atmospheric warming trend in the Northern Hemisphere, but does not lead to a persistent net cooling.
Due to the simulated THC shutdown the sea level at the North Atlantic shores rises by up to 80 cm by 2150, in addition to
the global sea level rise. This could potentially be a serious impact that requires expensive coastal protection measures.
A reduction of marine net primary productivity is associated with the impacts of warming rather than a THC shutdown. Regional
shifts in the currents in the Nordic Seas could strongly deteriorate survival chances for cod larvae and juveniles. This could
lead to cod fisheries becoming unprofitable by the end of the 21st century. While regional socioeconomic impacts might be
large, damages would be probably small in relation to the respective gross national products. Terrestrial ecosystem productivity
is affected much more by the fertilization from the increasing CO2 concentration than by a THC shutdown. In addition, the level of warming in the 22nd to 24th century favours crop production
in northern Europe a lot, no matter whether the THC shuts down or not. CO2 emissions corridors aimed at limiting the risk of a THC breakdown to 10% or less are narrow, requiring departure from business-as-usual
in the next few decades. The uncertainty about THC risks is still high. This is seen in model analyses as well as in the experts’
views that were elicited. The overview of results presented here is the outcome of the Integrated Assessment project INTEGRATION. 相似文献
49.
Matteo Barnabè Carlo Nipoti Léon V. E. Koopmans Simona Vegetti Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2009,393(4):1114-1126
We apply the joint lensing and dynamics code for the analysis of early-type galaxies, 'Combined Algorithm for Unified Lensing and Dynamics ReconstructiON ( cauldron )', to a rotating N -body stellar system with dark matter halo which significantly violates the two major assumptions of the method, i.e. axial symmetry supported by a two-integral distribution function. The goal is to study how cauldron performs in an extreme case, and to determine which galaxy properties can still be robustly recovered. Three data sets, corresponding to orthogonal lines of sight, are generated from the N -body system and analysed with the identical procedure followed in the study of real lens galaxies, adopting an axisymmetric power-law total density distribution. We find that several global properties of the N -body system are recovered with remarkable accuracy, despite the fact that the adopted power-law model is too simple to account for the lack of symmetry of the true density distribution. In particular, the logarithmic slope of the total density distribution is robustly recovered to within less than 10 per cent (with the exception of the ill-constrained very inner regions), the inferred angle-averaged radial profile of the total mass closely follows the true distribution, and the dark matter fraction of the system (inside the effective radius) is correctly determined within ∼10 per cent of the total mass. Unless the line-of-sight direction is almost parallel to the total angular momentum vector of the system, reliably recovered quantities also include the angular momentum, the V /σ ratio and the anisotropy parameter δ. We conclude that the cauldron code can be safely and effectively applied to real early-type lens galaxies, also providing reliable information for the systems that depart significantly from the method's assumptions. 相似文献
50.
James Binney Carlo Nipoti Filippo Fraternali 《Monthly notices of the Royal Astronomical Society》2009,397(4):1804-1815
We examine the proposal that the H i 'high-velocity' clouds (HVCs) surrounding the Milky Way and other disc galaxies form by condensation of the hot galactic corona via thermal instability. Under the assumption that the galactic corona is well represented by a non-rotating, stratified atmosphere, we find that for this formation mechanism to work the corona must have an almost perfectly flat entropy profile. In all other cases, the growth of thermal perturbations is suppressed by a combination of buoyancy and thermal conduction. Even if the entropy profile were nearly flat, cold clouds with sizes smaller than 10 kpc could form in the corona of the Milky Way only at radii larger than 100 kpc , in contradiction with the determined distances of the largest HVC complexes. Clouds with sizes of a few kpc can form in the inner halo only in low-mass systems. We conclude that unless even slow rotation qualitatively changes the dynamics of a corona, thermal instability is unlikely to be a viable mechanism for formation of cold clouds around disc galaxies. 相似文献