全文获取类型
收费全文 | 695篇 |
免费 | 12篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 101篇 |
地球物理 | 127篇 |
地质学 | 212篇 |
海洋学 | 30篇 |
天文学 | 167篇 |
综合类 | 4篇 |
自然地理 | 72篇 |
出版年
2023年 | 4篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 20篇 |
2013年 | 35篇 |
2012年 | 14篇 |
2011年 | 29篇 |
2010年 | 16篇 |
2009年 | 27篇 |
2008年 | 22篇 |
2007年 | 33篇 |
2006年 | 29篇 |
2005年 | 19篇 |
2004年 | 31篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 29篇 |
2000年 | 23篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 18篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 14篇 |
1983年 | 11篇 |
1981年 | 5篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1972年 | 3篇 |
1971年 | 12篇 |
排序方式: 共有716条查询结果,搜索用时 546 毫秒
651.
Combined photometry and radiometry of Iapetus can be used to investigate the nature of its surface and, in particular, the distribution of albedo that is responsible for the large variations in its visible and infrared brightness as it rotates. We present new 20-μm radiometric observations made in 1971–1973 and discuss these together with the photometric studies by Widorn (in 1949), Mills (in 1971), Noland et al. (in 1972–1973), and Franklin and Cook (in 1972–1974). The linear phase coefficient varies as the satellite rotates from 0.028 to 0.068 mag deg?1. When corrected for this effect, the photometric variations suggest an albedo distribution characterized by a dark area covering most of the leading hemisphere and a bright trailing hemisphere and bright south polar cap. A combined analysis of the photometry and radiometry yields a radius of 800 to 850 km and mean geometric albedos for the light and dark faces of about 0.35 and 0.07, respectively. The average phase integral of the bright hemisphere is between 1.0 and 1.5. We offer no explanation for the unique photometric properties of this satellite. 相似文献
652.
Brenda L. Murphy 《Natural Hazards》2007,41(2):297-315
This paper distinguishes between two types of emergency management at the local scale—municipal government responsibilities
and community-level initiatives. It argues that these are interdependent, but separate aspects of emergency management. Communities,
whether or not tied to particular places, are posited as being key, but often overlooked resources in both proactive and reactive
phases of emergency management. Of particular importance within communities are the social capital resources (networks of
strong and weak ties) that may work to improve a community’s resilience to risks and hazards. Two cases studies, the 2003
electricity power blackout in the eastern parts of both Canada and the United States and the 2000 water-borne disaster in
Walkerton are utilised to demonstrate the concepts developed in the paper. 相似文献
653.
A number of authors have reported the problem of unrealistic velocities (“rogue trajectories”) when computing the paths of
particles in a turbulent flow using modern Lagrangian stochastic (LS) models, and have resorted to ad hoc interventions. We
suggest that this problem stems from two causes: (1) unstable modes that are intrinsic to the dynamical system constituted
by the generalized Langevin equations, and whose actual triggering (expression) is conditional on the fields of the mean velocity
and Reynolds stress tensor and is liable to occur in complex, disturbed flows (which, if computational, will also be imperfect
and discontinuous); and, (2) the “stiffness” of the generalized Langevin equations, which implies that the simple stochastic
generalization of the Euler scheme usually used to integrate these equations is not sufficient to keep round-off errors under
control. These two causes are connected, with the first cause (dynamical instability) exacerbating the second (numerical instability);
removing the first cause does not necessarily correct the second, and vice versa. To overcome this problem, we introduce a
fractional-step integration scheme that splits the velocity increment into contributions that are linear (U
i
) and nonlinear (U
i
U
j
) in the Lagrangian velocity fluctuation vector U, the nonlinear contribution being further split into its diagonal and off-diagonal parts. The linear contribution and the
diagonal part of the nonlinear contribution to the solution are computed exactly (analytically) over a finite timestep Δt, allowing any dynamical instabilities in the system to be diagnosed and removed, and circumventing the numerical instability
that can potentially result in integrating stiff equations using the commonly applied explicit Euler scheme. We contrast results
using this and the primitive Euler integration scheme for computed trajectories in a drastically inhomogeneous urban canopy
flow. 相似文献
654.
Eugene Yee Ralph M. Gailis Alexander Hill Trevor Hilderman Darwin Kiel 《Boundary-Layer Meteorology》2006,121(3):389-432
We report on measurements of the near-field dispersion of contaminant plumes in a large array of building-like obstacles at three scales; namely, at full-scale in a field experiment, at 1:50 scale in a wind-tunnel simulation, and at 1:205 scale in a water-channel simulation. Plume concentration statistics extracted from the physical modelling in the wind-tunnel and water-channel simulations are compared to those obtained from a field experiment. The modification of the detailed structure of the plume as it interacts with the obstacles is investigated. To this purpose, measurements of the evolution of the mean concentration, concentration fluctuation intensity, concentration probability density function, and integral time scale of concentration fluctuations in the array plume obtained from the field experiment and the scaled wind-tunnel and water-channel experiments are reported and compared, as well as measurements of upwind and within-array velocity spectra. Generally, the wind-tunnel and water-channel results on the modification of the detailed plume structure by the obstacles were qualitatively similar to those observed in the field experiments. However, with the appropriate scaling, the water-channel simulations were able to reproduce quantitatively the results of the full-scale field experiments better than the wind-tunnel simulations. 相似文献
655.
Rosemary Charlton Rowan Fealy Sonja Moore John Sweeney Conor Murphy 《Climatic change》2006,74(4):475-491
Estimates are made of changes in effective runoff at a high spatial resolution for the island of Ireland under different climate
change scenarios. The first part of the investigation examines changes in annual and seasonal effective runoff for the whole
land area of Ireland. The rainfall-runoff model HYSIM is used to carry out the hydrological simulations. The output from the
HadCM3 Global Climate Model (GCM) is downscaled using statistical techniques to provide precipitation and evaporation data
at a 10 km × 10 km resolution; this data is then used to drive the HYSIM model. Simulations are carried out for each of the
825 10 km × 10 km grid cells covering Ireland for the baseline period (1961–1990) and two future scenarios; 2041–2070 and
2061–2090. Parameter values are derived for each square using data from the Soil Survey of Ireland and the CORINE land use
database and validation is carried out for selected catchments. The results of these simulations indicate a decrease in annual
runoff that is most marked in the east and southeast of the country, whereas an increase is likely for the extreme northwest.
The reduction in effective runoff for the east of the country is particularly marked during the summer months. It is these
areas that have highest population density and also where greatest population growth is likely to occur. During the winter
months an increase in effective runoff is suggested for the western half of country which could have implications for flood
frequency, as well as the extent and duration of winter flooding. 相似文献
656.
Towards quantifying uncertainty in transient climate change 总被引:2,自引:3,他引:2
Matthew Collins Ben B. B. Booth Glen R. Harris James M. Murphy David M. H. Sexton Mark J. Webb 《Climate Dynamics》2006,27(2-3):127-147
Ensembles of coupled atmosphere–ocean global circulation model simulations are required to make probabilistic predictions of future climate change. “Perturbed physics” ensembles provide a new approach in which modelling uncertainties are sampled systematically by perturbing uncertain parameters. The aim is to provide a basis for probabilistic predictions in which the impact of prior assumptions and observational constraints can be clearly distinguished. Here we report on the first perturbed physics coupled atmosphere–ocean model ensemble in which poorly constrained atmosphere, land and sea-ice component parameters are varied in the third version of the Hadley Centre model (the variation of ocean parameters will be the subject of future study). Flux adjustments are employed, both to reduce regional sea surface temperature (SST) and salinity biases and also to admit the use of combinations of model parameter values which give non-zero values for the global radiation balance. This improves the extent to which the ensemble provides a credible basis for the quantification of uncertainties in climate change, especially at a regional level. However, this particular implementation of flux-adjustments leads to a weakening of the Atlantic overturning circulation, resulting in the development of biases in SST and sea ice in the North Atlantic and Arctic Oceans. Nevertheless, model versions are produced which are of similar quality to the unperturbed and un-flux-adjusted version. The ensemble is used to simulate pre-industrial conditions and a simple scenario of a 1% per year compounded increase in CO2. The range of transient climate response (the 20 year averaged global warming at the time of CO2 doubling) is 1.5–2.6°C, similar to that found in multi-model studies. Measures of global and large scale climate change from the coupled models show simple relationships with associated measures computed from atmosphere-mixed-layer-ocean climate change experiments, suggesting that recent advances in computing the probability density function of climate change under equilibrium conditions using the perturbed physics approach may be extended to the transient case. 相似文献
657.
Understanding how Holocene sea levels influenced coastal wetland development in the Caribbean will aid wetland management in the context of predicted sea level rise. Nine radiocarbon dates from the Maracas and Nariva Swamps on wave-dominated coasts from Trinidad, show sea level was –9 m approximately 7000 yr BP, and rose gradually to –2 m by 2000 yr BP. Since then there may have been isostatic readjustment. Wetlands developed with a transgression of dry upland habitats by rising seas and the facultative halophyte Rhizophora colonized the new brackish water environment. A freshwater plant community gradually replaced the Rhizophora as the marine influence decreased. At Maracas, higher sea levels caused wetland retreat as beach and lagoon habitats migrated inland. Sand ridges in Nariva Swamp indicate that, as in Maracas Swamp, sea level rise created beaches and lagoons, but that these landforms prograded as additional nearshore sediments were deposited. Basins were also filled with sediment delivered by streams that drain the watershed, and by mangrove peat accumulation. 相似文献
658.
Regional growth curves (RGCs) have been recently used to provide a new basis for removing nonclimatic trend from tree-ring data. Here we propose a different use for RGCs and explore their properties along two transects, one meridional and the other elevational. RGCs consisting of mean ring width plotted against cambial age were developed for larch samples from 34 sites along a meridional transect (55-72°N) in central Siberia, and for 24 sites on an elevational gradient (1120 and 2350 m a.s.l.) in Tuva and neighboring Mongolia at approximately 51°N. There are systematic gradients of the parameters of the RGCs, such as I0-maximum tree-ring width near pith, and Imin, the asymptotic value of tree-ring width in old trees. They are smaller at higher latitude and elevation. Annual mean temperature and mean May-September temperature are highly correlated with latitude here, and hence RGC parameters are correlated with these climatic variables. Correlations with precipitation are more complex, and contradictory between meridional and elevational transects. The presence of a similar gradient in the elevational transect is consistent with temperature being the causal factor for both gradients, rather than, for example, latitude-dependent patterns of seasonal photoperiod change. Taking ring measurements from collections of relict and subfossil wood, the RGC-latitude and RGC-temperature relationships are used to estimate paleo-temperatures on centennial time scales. These estimates are consistent with earlier “traditional” dendroclimatic approaches, and with independent information on the northern extent of forest growth in the early mid-Holocene. It may be possible to use this same approach to make estimates of century-scale paleo-temperatures in other regions where abundant relict wood is present. 相似文献
659.
Thomas L. Pratt Mark Holmes Eugene S. Schweig Joan Gomberg Hugh A. Cowan 《Tectonophysics》2003,368(1-4):211
High-resolution seismic reflection profiles from Limón Bay, Republic of Panama, were acquired as part of a seismic hazard investigation of the northern Panama Canal region. The seismic profiles image gently west and northwest dipping strata of upper Miocene Gatún Formation, unconformably overlain by a thin (<20 m) sequence of Holocene muds. Numerous faults, which have northeast trends where they can be correlated between seismic profiles, break the upper Miocene strata. Some of the faults have normal displacement, but on many faults, the amount and type of displacement cannot be determined. The age of displacement is constrained to be Late Miocene or younger, and regional geologic considerations suggest Pliocene movement. The faults may be part of a more extensive set of north- to northeast-trending faults and fractures in the canal region of central Panama. Low topography and the faults in the canal area may be the result of the modern regional stress field, bending of the Isthmus of Panama, shearing in eastern Panama, or minor deformation of the Panama Block above the Caribbean subduction zone. For seismic hazard analysis of the northern canal area, these faults led us to include a source zone of shallow faults proximal to northern canal facilities. 相似文献
660.
Maps are presented of 3 P 1 →3 P 0 [C i ] and J =2→1 C18 O line emission from the interstellar molecular cloud G35.2−0.74N. The maps are interpreted with reference to a previous model for the structure of the cloud in which opposing jets from a central object, embedded in a rotating interstellar disc, precess and drive a bipolar molecular outflow. The C18 O emission traces the rotating interstellar disc, but the [C i ] emission shows several features. An unresolved component is observed which probably results from dissociation of CO in the centre of the disc by UV radiation from the central source. Background [C i ] emission is also observed which shares the rotation of the disc on larger scales. The C i /CO ratio in these components is typically a few per cent. High-velocity [C i ] emission, where C i /CO is high (>0.1–0.4), is observed between the CO molecular outflow and the cavity exacavated by the jet. This material has probably been accelerated by the jet but dissociated by far-UV radiation propagating through the cavity. The C i /CO ratio falls as the shocked outflow later sweeps up CO. 相似文献