全文获取类型
收费全文 | 178篇 |
免费 | 23篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 17篇 |
地球物理 | 58篇 |
地质学 | 68篇 |
海洋学 | 11篇 |
天文学 | 28篇 |
综合类 | 4篇 |
自然地理 | 7篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 8篇 |
2019年 | 3篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 13篇 |
2013年 | 15篇 |
2012年 | 3篇 |
2011年 | 13篇 |
2010年 | 10篇 |
2009年 | 16篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有201条查询结果,搜索用时 156 毫秒
121.
Temporal evolution of surface humidity in Spain: recent trends and possible physical mechanisms 总被引:1,自引:0,他引:1
Sergio M. Vicente-Serrano Cesar Azorin-Molina Arturo Sanchez-Lorenzo Enrique Morán-Tejeda Jorge Lorenzo-Lacruz Jesús Revuelto Juan I. López-Moreno Francisco Espejo 《Climate Dynamics》2014,42(9-10):2655-2674
We analyzed the evolution of surface relative humidity (RH) and specific humidity (q) in Spain, based on complete records available from the State Meteorological Agency of Spain. The surface RH records used span the period 1920–2011, but because of spatial and temporal constraints in the dataset we used a subset of the data, covering the period 1961–2011. The subset contained 50 monthly series of RH, which were created through a process of quality control, reconstruction and homogenization. The data shows that there was a large decrease in RH over mainland Spain from 1961 to 2011, which was greatest in spring and summer. In contrast, there was no overall change in the specific humidity in this period, except in spring, when an increase was observed. The decrease in RH affected the entire country, but the changes in specific humidity were less homogeneous. For specific humidity there was a general increase in the northern and eastern parts of Spain, whereas negative trends dominated in the central and southern areas, mainly during the summer months. The results suggest that an increase in the water holding capacity of the atmosphere as a consequence of warming during recent decades has not been accompanied by an increase in the surface water vapor content, probably because the supply of water vapor from the main terrestrial and oceanic areas has been constrained. We discuss the implications of these findings for evapotranspiration processes, precipitation and water management in Spain. 相似文献
122.
Remediation of contaminated aquifers demands a reliable characterization of hydraulic connectivity patterns. Hydraulic diffusivity is possibly the best indicator of connectivity. It can be derived using the tidal response method (TRM), which is based on fitting observations to a closed-form solution. Unfortunately, the conventional TRM assumes homogeneity. The objective of this study was to overcome this limitation and use tidal response to identify preferential flowpaths. Additionally, the procedure requires joint inversion with hydraulic test data. These provide further information on connectivity and are needed to resolve diffusivity into transmissivity and storage coefficient. Spatial variability is characterized using the regularized pilot points method. Actual application may be complicated by the need to filter tidal effects from the response to pumping and by the need to deal with different types of data, which we have addressed using maximum likelihood methods. Application to a contaminated artificial coastal fill leads to flowpaths that are consistent with the materials used during construction and to solute transport predictions that compare well with observations. We conclude that tidal response can be used to identify connectivity patterns. As such, it should be useful when designing measures to control sea water intrusion. 相似文献
123.
Martín Lara Jesús F. Palacián Ryan P. Russell 《Celestial Mechanics and Dynamical Astronomy》2010,108(1):1-22
Preliminary mission design for planetary satellite orbiters requires a deep knowledge of the long term dynamics that is typically
obtained through averaging techniques. The problem is usually formulated in the Hamiltonian setting as a sum of the principal
part, which is given through the Kepler problem, plus a small perturbation that depends on the specific features of the mission.
It is usually derived from a scaling procedure of the restricted three body problem, since the two main bodies are the Sun
and the planet whereas the satellite is considered as a massless particle. Sometimes, instead of the restricted three body
problem, the spatial Hill problem is used. In some cases the validity of the averaging is limited to prohibitively small regions,
thus, depriving the analysis of significance. We find this paradigm at Enceladus, where the validity of a first order averaging
based on the Hill problem lies inside the body. However, this fact does not invalidate the technique as perturbation methods
are used to reach higher orders in the averaging process. Proceeding this way, we average the Hill problem up to the sixth
order obtaining valuable information on the dynamics close to Enceladus. The averaging is performed through Lie transformations
and two different transformations are applied. Firstly, the mean motion is normalized whereas the goal of the second transformation
is to remove the appearance of the argument of the node. The resulting Hamiltonian defines a system of one degree of freedom
whose dynamics is analyzed. 相似文献
124.
Antonio Pedrera Jesús Galindo-Zaldívar Ana Ruíz-Constán Carlos Duque Carlos Marín-Lechado Inmaculada Serrano 《Tectonophysics》2009,463(1-4):145-160
Rheological heterogeneities in the upper-crust have a close relationship with the fold position where rigid bodies could constitute initial perturbations that allow the nucleation of folds. Consequently, establish the position and geometry of anomalous rocks located in the upper-crust by geophysical studies help to understand the folded structure observed on surface. New geological observations in the field, along with gravity, magnetic, magnetotelluric and seismicity data, reveal the subsurface structure in the Sierra de Los Filabres–Sierra de Las Estancias folded region part of the Alpine belt in southern Spain. The geometry of the upper crust is determined by geological field data, 2D gravity models, 2D magnetic models and 2D MT resistivity model, while seismicity evidences the location of the deep active structures. These results allow us to propose that a basic rock body at 4 to 9 km depth has determined the nucleation and development of the Sierra de Los Filabres kilometric antiform. N-vergent large late folds are subjected to a variable present-day stress field. Earthquake focal mechanisms suggest the presence in depth of a regional NW–SE compressive stress field. However, most of the seismogenetic structures do not extend up to the surface, where NW–SE and WNW–ESE outcropping active normal faults are observed, thus indicating a NE–SW extension in the upper crust simultaneous to orthogonal NW–SE compression related to reverse faults and minor folds developed in the Eastern Almanzora Corridor and in the nearby Huércal–Overa Basin. The recent and active tectonic studies of cordilleras hinterland subjected to late folding greatly benefits from the integration of surface observations together with geophysical data. 相似文献
125.
César Viseras Juan Fernández Fernando García-García Jesús M. Soria María Luisa Calvache Pedro Jáuregui 《Environmental Geology》2009,56(7):1353-1369
An analysis has been made of sedimentary systems involved in the rapid silting of a reservoir constructed in 1974 in Alhama
de Granada (S. Spain); in only 30 years the storage capacity of the reservoir has shrunk by 80% and its perimeter has decreased
by 64%. A study of sediment lithofacies identified in a series of shallow trenches and of georadar facies identified in a
series of almost 900 m lines of ground penetrating radar (GPR) images, together with a survey of surface geology, has identified
3 alluvial systems (2 transversal systems and a longitudinal system) whose deltas have filled in the reservoir. Thus, there
are three phases in the evolution of the reservoir siltation: (1) an initial stage (1974–1977) typified by northward progradation
of the longitudinal river delta of about 100 m year−1 and an eastward progradation of the transversal system delta of about 20 m year−1; (2) an intermediate stage (1977–1984) in which the longitudinal river delta progradation slowed to 25 m year−1 and the axial drainage became obstructed due to the considerable eastward progradation of the transversal delta; and (3)
a final phase (1984–present) in which there have been few changes in the areal distribution of the deltas apart from a southeastward
expansion of the transversal delta. Generally, aggradational growth patterns (vertical accretion) have dominated in this final
phase. The lithology of the source area, the slope and precipitation distribution has a significant effect not only on the
sediment supply, but also indirectly on the creation of accommodation space and on the evolution of stratal growth patterns. 相似文献
126.
Submillimeter observations with ALMA will be the essential next step in our understanding of how stars and planets form. Key
projects range from detailed imaging of the collapse of pre-stellar cores and measuring the accretion rate of matter onto
deeply embedded protostars, to unravelling the chemistry and dynamics of high-mass star-forming clusters and high-spatial
resolution studies of protoplanetary disks down to the 1 AU scale. 相似文献
127.
Brenda Matthews Edwin Bergin Antonio Crapsi Michiel Hogerheijde Jes Jørgensen Dan Marrone Ramprasand Rao 《Astrophysics and Space Science》2008,313(1-3):65-68
We present our most recent results from an ongoing study of the Class 0 source Barnard 1c in Perseus. This source is of particular
interest because it exhibits evidence of strong alignment of grains all the way to the core’s centre, which is contrary to
all other low-mass protostellar cores observed to date. Our goal is to clarify the source of poor alignment in other sources
by identifying the source of strong alignment in B1c. A central cavity has been identified in N2H+ emission; its anticorrelation with C18O emission suggests that heating in the centre has released CO from grain mantles, in turn destroying N2H+. We present sensitivity-limited, high spatial resolution polarimetry data from the SubMillimeter Array and discuss the potential
implications of these data. 相似文献
128.
Izaskun Jiménez-Serra Jesús Martín-Pintado Arturo Rodríguez-Franco Paola Caselli Serena Viti Tom Hartquist 《Astrophysics and Space Science》2008,313(1-3):159-163
We present the first C-shock and radiative transfer model that calculates the evolution of the line profiles of neutral and
ion species like SiO, H13CO+ and HN13C for different flow times along the propagation of the shock through the unperturbed gas. We find that the line profiles
of SiO characteristic of the magnetic precursor stage have very narrow linewidths and are centered at velocities close to
the ambient cloud velocity, as observed toward the young shocks in the L1448-mm outflow. Consistently with previous works,
our model also reproduces the broad SiO emission detected in the high velocity gas in this outflow, for the downstream postshock
gas in the shock. This implies that the different velocity components observed in L1448-mm are due to the coexistence of different
shocks at different evolutionary stages. 相似文献
129.
130.
Guillermo Curado Juan E. Sánchez-Moyano Enrique Figueroa Jesús M. Castillo 《Estuaries and Coasts》2014,37(3):589-601
Ecological restoration of salt marshes using plantations may enhance the macroinvertebrate community, but little is known about the development of benthic macroinvertebrates after ecological engineering projects in European salt marshes. This study analyzed the environment and the macroinvertebrate community in European salt marshes 3 years after restoration using Spartina maritima plantations in comparison with non-restored and preserved marshes in Odiel Marshes (Southwest Iberian Peninsula). We hypothesized that planting Spartina maritima on intertidal mudflats would increase species richness and diversity (Shannon–Weaver index) of the benthic macroinvertebrate community by increasing environmental heterogeneity, providing feeding resources and improving sediments characteristics. Benthic macrofauna samples (composed mainly of annelids, crustaceans, and mollusks) were sampled in plots of 20 cm?×?25 cm to 5 cm depth between +1.8 and +3.0 m above Spanish Hydrographic Zero. Sediment organic matter content, bulk density, pH, and redox potential were the variables that best explained macroinvertebrate distribution. Restored marshes achieved similar diversity and even higher specific richness than preserved marshes, although with differences in species composition. Non-restored marshes showed the lowest diversity. Restored and preserved marshes did not differ in total abundance or biomass of macroinvertebrates, both being higher than in non-restored marshes. The macroinvertebrate communities in preserved and non-restored marshes showed the largest difference in taxa composition, with restored marshes occupying an intermediate position. Salt marsh restoration using S. maritima increased the complexity (ecological diversity and species richness) and abundance of the benthic macroinvertebrate community. Our study offers new information about the role of salt marsh plants in mediating faunal communities via ecological engineering projects. 相似文献