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121.
Thomas Boelens Henk Schuttelaars George Schramkowski Tom De Mulder 《Ocean Dynamics》2018,68(10):1285-1309
A new depth-averaged exploratory model has been developed to investigate the hydrodynamics and the tidally averaged sediment transport in a semi-enclosed tidal basin. This model comprises the two-dimensional (2DH) dynamics in a tidal basin that consists of a channel of arbitrary length, flanked by tidal flats, in which the water motion is being driven by an asymmetric tidal forcing at the seaward side. The equations are discretized in space by means of the finite element method and solved in the frequency domain. In this study, the lateral variations of the tidal asymmetry and the tidally averaged sediment transport are analyzed, as well as their sensitivity to changes in basin geometry and external overtides. The Coriolis force is taken into account. It is found that the length of the tidal basin and, to a lesser extent, the tidal flat area and the convergence length determine the behaviour of the tidally averaged velocity and the overtides and consequently control the strength and the direction of the tidally averaged sediment transport. Furthermore, the externally prescribed overtides can have a major influence on tidal asymmetry in the basin, depending on their amplitude and phase. Finally, for sufficiently wide tidal basins, the Coriolis force generates significant lateral dynamics. 相似文献
122.
A proposal for a new scenario framework to support research and assessment in different climate research communities 总被引:1,自引:0,他引:1
Detlef P. van Vuuren Keywan Riahi Richard Moss Jae Edmonds Allison Thomson Nebojsa Nakicenovic Tom Kram Frans Berkhout Rob Swart Anthony Janetos Steven K. Rose Nigel Arnell 《Global Environmental Change》2012,22(1):21-35
In this paper, we propose a scenario framework that could provide a scenario “thread” through the different climate research communities (climate change – vulnerability, impact, and adaptation - and mitigation) in order to support assessment of mitigation and adaptation strategies and climate impacts. The scenario framework is organized around a matrix with two main axes: radiative forcing levels and socio-economic conditions. The radiative forcing levels (and the associated climate signal) are described by the new Representative Concentration Pathways. The second axis, socio-economic developments comprises elements that affect the capacity for mitigation and adaptation, as well as the exposure to climate impacts. The proposed scenarios derived from this framework are limited in number, allow for comparison across various mitigation and adaptation levels, address a range of vulnerability characteristics, provide information across climate forcing and vulnerability states and span a full century time scale. Assessments based on the proposed scenario framework would strengthen cooperation between integrated-assessment modelers, climate modelers and vulnerability, impact and adaptation researchers, and most importantly, facilitate the development of more consistent and comparable research within and across these research communities. 相似文献
123.
Benjamin D. Santer Karl E. Taylor Tom M. L. Wigley Joyce E. Penner Philip D. Jones Ulrich Cubasch 《Climate Dynamics》1995,12(2):77-100
It has been hypothesized recently that regional-scale cooling caused by anthropogenic sulfate aerosols may be partially obscuring
a warming signal associated with changes in greenhouse gas concentrations. Here we use results from model experiments in which
sulfate and carbon dioxide have been varied individually and in combination in order to test this hypothesis. We use centered
[R (t)] and uncentered [C (t)] pattern similarity statistics to compare observed time-evolving surface temperature change patterns with the model-predicted
equilibrium signal patterns. We show that in most cases, the C (t) statistic reduces to a measure of observed global-mean temperature changes, and is of limited use in attributing observed
climate changes to a specific causal mechanism. We therefore focus on R (t), which is a more useful statistic for discriminating between forcing mechanisms with different pattern signatures but similar
rates of global mean change. Our results indicate that over the last 50 years, the summer (JJA) and fall (SON) observed patterns
of near-surface temperature change show increasing similarity to the model-simulated response to combined sulfate aerosol/CO2 forcing. At least some of this increasing spatial congruence occurs in areas where the real world has cooled. To assess the
significance of the most recent trends in R (t) and C (t), we use data from multi-century control integrations performed with two different coupled atmosphere-ocean models, which
provide information on the statistical behavior of 'unforced' trends in the pattern correlation statistics. For the combined
sulfate aerosol/CO2 experiment, the 50-year R (t) trends for the JJA and SON signals are highly significant. Results are robust in that they do not depend on the choice of
control run used to estimate natural variability noise properties. The R (t) trends for the CO2-only signal are not significant in any season. C (t) trends for signals from both the CO2-only and combined forcing experiments are highly significant in all seasons and for all trend lengths (except for trends
over the last 10 years), indicating large global-mean changes relative to the two natural variability estimates used here.
The caveats regarding the signals and natural variability noise which form the basis of this study are numerous. Nevertheless,
we have provided first evidence that both the largest-scale (global-mean) and smaller-scale (spatial anomalies about the global
mean) components of a combined CO2/anthropogenic sulfate aerosol signal are identifiable in the observed near-surface air temperature data. If the coupled-model
noise estimates used here are realistic, we can be highly confident that the anthropogenic signal that we have identified
is distinctly different from internally generated natural variability noise. The fact that we have been able to detect the
detailed spatial signature in response to combined CO2 and sulfate aerosol forcing, but not in response to CO2 forcing alone, suggests that some of the regional-scale background noise (against which we were trying to detect a CO2-only signal) is in fact part of the signal of a sulfate aerosol effect on climate. The large effect of sulfate aerosols found
in this study demonstrates the importance of their inclusion in experiments designed to simulate past and future climate change.
Received: 10 November 1994 / Accepted: 19 July 1995 相似文献
124.
Lisa K. Whalley Kate L. Furneaux Tom Gravestock Helen M. Atkinson Catherine S. E. Bale Trevor Ingham William J. Bloss Dwayne E. Heard 《Journal of Atmospheric Chemistry》2007,58(1):19-39
A Laser Induced Fluorescence (LIF) instrument has been developed to detect iodine monoxide (IO) radicals in the atmosphere.
An all solid-state Nd:YAG pumped Ti:Sapphire laser operating at approximately 445 nm was used to excite the (2,0) band of
the IO A2Π3/2 ← X2Π3/2 electronic transition, with off-resonance fluorescence in the (2,5) band detected at 521 nm. The sensitivity of the instrument
was determined by calibration. IO (between 10 and 150 pptV) was generated following the 184.9 nm photolysis of N2O/CF3I/N2 mixtures with O3 actinometry used to determine the photolysis flux. The detection limit was determined to be 0.3 pptV for a 300 s integration
period, with an uncertainty of 23% (1σ). The instrument was deployed in August/September 2006 during the RHaMBLe (Reactive Halogens in the Marine Boundary Layer)
campaign in Roscoff, France. Located on a small jetty, a few metres from the water’s edge at high tide, the instrument measured
significant levels of IO on 11 days, with a maximum of 27.6 ± 3.2 pptV observed on one day (averaged over 10 s) representing
the highest IO mixing ratio recorded in the marine boundary layer to date. IO displayed a clear diurnal profile with a maximum
at low tide during the daytime. These results represent the first point measurements of IO in the atmosphere by LIF. 相似文献
125.
On using mixed-layer transport parameterizations with radiometric surface temperature for computing regional scale sensible heat flux 总被引:4,自引:0,他引:4
Recent mixed-layer formulations for computing large-scale surface energy fluxes under daytime convective conditions do not require the estimation of surface-layer parameters, such as the roughness lengths for momentum and heat. This greatly simplifies approaches using operational satellite measurements of surface temperature for computing the surface energy balance at regional scales because the surface roughness parameters are not well known for many landscapes. The utility of such mixed-layer formulations is tested using data from several recent multidisciplinary field experiments (HAPEX-MOBILHY, FIFE and Monsoon 90). The results indicate that specific mixed-layer formulations adequately simulate surface sensible heat fluxes in the grassland and shrubland sites. However, use of the original values of proposed empirical coefficients for the forested site yield poor results. This is probably due to the fact that the forested site has significantly different surface geometry and associated distribution of temperature among the surface components (especially the relative importance of soil background temperatures) compared to the other sites. Therefore, the relationship between aerodynamic and radiometric surface temperature may have greatly differed between the forested site and the other locations. However, differences in aerodynamic roughness between the experimental sites were not correlated with changes required in the values of the coefficients. Instead, a two-source model which makes the distinction between aerodynamic and radiative temperature is proposed, as a means to determine which surface properties significantly affect the magnitude of the mixed-layer coefficients. 相似文献
126.
The Westerly Index as complementary indicator of the North Atlantic oscillation in explaining drought variability across Europe 总被引:1,自引:0,他引:1
127.
The most appropriate indices with which to quantify Australian bushfire danger are the McArthur fire danger meters. These meters use meteorological information to produce a fire danger index that is directly related to the chance of a fire starting - and to the severity of a fire once it has started. The Mark 5 forest-fire danger meter uses air temperature, relative humidity and wind speed, plus a drought factor that is calculated using daily rainfall and temperature information.Three years of daily data generated from the CSIRO four-level general circulation model, and thirty years of daily data generated from the CSIRO nine-level model were used to estimate the daily McArthur forest fire danger index for simulations corresponding to present conditions, and to those corresponding to doubled atmospheric CO2. The performance of these models with respect to fire danger was tested by comparing the fire danger index for Sale (in the Eastern part of Victoria, South-eastern Australia) calculated from analysis of daily climatological data with the modelled annual cumulative forest fire danger index for the grid point that was representative of Sale. Data from both models for all Australian grid points were also examined. Both models predict an increase in fire danger over much of Australia for their doubled CO2 scenarios.The results from the models confirm that annually averaged daily relative humidity is the single most important variable in the estimation of forest fire danger on an annual basis, yet the models tend to produce relative humidities that are slightly too low so that the fire danger is overestimated. A simple one-box model of evaporation indicates that the value of relative humidity to be expected under an altered climatic regime depends on the modelled relation between actual and potential evaporation, the present values of relative humidity and evaporation rate, as well as on the expected changes in wind speed. 相似文献
128.
Risk analysis and appraisal of the benefits of structural flood risk management measures such as embankments is well established. Here, a method to quantify, over extended timescales, the effectiveness of non-structural measures such as land use spatial planning, insurance and flood resilient construction is presented. The integrated approach couples socio-economic and climate change scenarios with long term land use modelling and flood risk analysis to generate maps and time series of expected annual damages. The analysis has been applied on a case study in the Thames Estuary in the UK. Stakeholders helped develop a number of scenarios that might lead to substantial changes in existing planning and insurance policies in the UK. The effectiveness of these changes was analysed and showed the substantial benefits in terms of reduction of future flood risks that are achievable with changes in planning policy, financial incentives and resilient property construction in the floodplain. Moreover, the reward can be increased through earlier action. Subsequently, the benefits of a range of policies are explored under the UK Foresight socio-economic scenarios. Different structural and non structural flood management interventions are tested and the results demonstrate that despite the potential for large increases in flood risk in the Thames Estuary, in all scenarios substantial flood risk reductions are possible. The effectiveness of non-structural measures is however sensitive to socio-economic changes and governance arrangements. The analysis described here will help to identify portfolios of non-structural and structural options that are robust to uncertainties. 相似文献
129.
We focus on an island wake episode that occurred in the Madeira Archipelago region of the north-east Atlantic at $32.5^{\circ }\mathrm{N}, 17^{\circ }\mathrm{W}$ . The Weather Research and Forecasting numerical model was used in a (one-way) downscaling mode, considering initial and boundary conditions from the European Centre for Medium-range Weather Forecasts system. The current literature emphasizes adiabatic effects on the dynamical aspects of atmospheric wakes. Changes in mountain height and consequently its relation to the atmospheric inversion layer should explain the shift in wake regimes, from a ‘strong-wake’ to ‘weak-wake’ scenario. Nevertheless, changes in sea-surface temperature variability in the lee of an island can induce similar regime shifts because of exposure to stronger solar radiation. Increase in evaporation contributes to the enhancement of convection and thus to the uplift of the stratified atmospheric layer above the critical height, with subsequent internal gravity wave activity. 相似文献
130.
Tom Jacob 《Climate Policy》2013,13(1):91-97
What is the significance of the 2007 United Nations Climate Change Conference in Bali? The formal outcomes, especially the ‘Bali Action Plan’, are described and commented on, along with the challenges for negotiating a post-2012 agreement in Copenhagen during 2008 and 2009. The article concludes that the outcome of the Bali meeting is insufficient when compared to the nature of the challenge posed by climate change. However, it can nevertheless be considered a success in terms of ‘Realpolitik’ in paving the way for the negotiations ahead, because some real changes have been discerned in the political landscape. The challenges for the road towards Copenhagen are manifold: the sheer volume and complexity of the issues and the far-reaching nature of decisions such as differentiation between non- Annex I countries pose significant challenges in themselves, while the dependency on the electoral process in the USA introduces a high element of risk into the whole process. The emergence of social justice as an issue turns climate policy into an endeavour to improve the world at large—thereby adding to the complexity. And, finally, the biggest challenge is the recognition that the climate problem requires a global solution, that Annex I and non-Annex I countries are mutually dependent on each other and that only cooperation regarding technology in combination with significant financial support will provide the chance to successfully tackle climate change. 相似文献