全文获取类型
收费全文 | 514篇 |
免费 | 35篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 53篇 |
地球物理 | 154篇 |
地质学 | 198篇 |
海洋学 | 32篇 |
天文学 | 63篇 |
综合类 | 1篇 |
自然地理 | 33篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 38篇 |
2015年 | 26篇 |
2014年 | 28篇 |
2013年 | 32篇 |
2012年 | 33篇 |
2011年 | 20篇 |
2010年 | 27篇 |
2009年 | 39篇 |
2008年 | 30篇 |
2007年 | 32篇 |
2006年 | 14篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 7篇 |
2001年 | 8篇 |
2000年 | 17篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1948年 | 2篇 |
1941年 | 1篇 |
排序方式: 共有552条查询结果,搜索用时 15 毫秒
141.
An extension of an existing analytical solution for the response of a flexible retaining wall subjected to seismic loading is presented. The solution is based on the assumption that the wall and the soil remain elastic and that there are no shear stresses at the wall–soil interface while the contact remains tied. In addition to the wall displacements due to bending, the wall can experience rigid‐body motions due to rotation and horizontal and vertical movements. The solution is verified by comparing its results with those of a finite element method. Results from the analytical solution together with those of the (FEM) are used to identify and quantify the relative importance of key parameters on the seismic response of a wall. The study shows that wall flexibility and horizontal rigid‐body motions of the wall and frequency content of the seismic input have a significant effect on the wall loads. The pressures behind a rigid wall decrease as the wall rotates about its base, whereas for a flexible wall, the soil pressures decrease as the friction between the backfill and the wall increases. The rigid‐body vertical movements of a wall have little impact on the dynamic pressures induced in the wall, except for a flexible wall where, when prevented, the dynamic loads may be reduced. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
142.
In this article, we estimated the alpha parameter of the Priestley–Taylor model under rain‐fed conditions. This study was conducted in an oat crop, from 7 September to 22 October 2009, in a region of subhumid plains (Tandil, Argentina). An energy balance station was installed within the experimental field to monitor its development. The alpha parameter value obtained was 1.41 ± 0.01, which led to an overestimation of the evapotranspiration of just 2% and a relative error in estimating evapotranspiration of 8%. The results suggest that the alpha parameter obtained is adequate in estimating the evapotranspiration of oat crops or similar crops in subhumid plains of Buenos Aires, Argentina. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
143.
Novelo-Casanova David A. Suárez Gerardo Cabral-Cano Enrique Fernández-Torres Enrique A. Fuentes-Mariles Oscar A. Havazli Emre Jaimes Miguel Á. López-Espinoza Erika D. Martin-Del Pozzo Ana Lillian Morales-Barrera Wendy V. Morales-Rodríguez Hipólito L. Nieto-Torres Amiel Rodríguez-Elizarrarás Sergio R. Solano-Rojas Darío Velasco-Herrera Victor M. 《Natural Hazards》2022,111(1):411-437
Natural Hazards - We present a Risk Atlas of Mexico City based on a Geographical Information System (RA-GIS). We identified the prevalent social risk to the more relevant hazards in Mexico City... 相似文献
144.
Comparative phylogeography and population genetic structure of three widespread mollusc species in the Mediterranean and near Atlantic
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Although several studies have evaluated the genetic structure and phylogeographic patterns in many species of marine invertebrates, a general model that applies to all of them remains elusive. For example, some species present an admixture of populations with high gene flow, whereas others exhibit more complex patterns characterized by small‐scale unstructured genetic heterogeneity, even at a local scale. These differences are thought to be due to clear biological aspects such as direct versus indirect development, or the presence of lecithotrophic versus planktotrophic larvae, but few studies compare animals with similar distributions and life modes. Here, we explore the phylogeographic and genetic structure patterns in two chiton (Chiton olivaceus and Lepidopleurus cajetanus) and one abalone (Haliotis tuberculata) species co‐occurring in the same habitat. Samples were obtained from shallow rocky bottoms along the Iberian Peninsula (Atlantic and Mediterranean coasts), Italy, Croatia and Greece, and the mitochondrial markers COI and 16S rRNA gene were sequenced. Our data show evidence of admixture and population expansion in C. olivaceus and H. tuberculata, whereas L. cajetanus exhibited a ‘chaotic patchiness’ pattern defined by a high genetic variability with locality‐exclusive haplotypes, high genetic divergence, and a lack of geographic structure. Shared haplotypes were sampled in both coasts of Iberia (for H. tuberculata) and in the Western and Eastern Mediterranean (for C. olivaceus), potentially indicating high dispersal ability and a recent expansion. The processes underlying the fine‐scale structuring in L. cajetanus remain a mystery. These results are especially interesting because the reproductive mode of the two chitons is similar but differs from that of the abalone, with a veliger larva, while instead the genetic structure of C. olivaceus and H. tuberculata are similar, thus contrasting with predictions based on the life history of the three molluscs and showing that the genetic patterns of marine species may be shaped by many factors, including historical ones. 相似文献
145.
J. Fernández C. Primo A. S. Cofiño J. M. Gutiérrez M. A. Rodríguez 《Climate Dynamics》2009,33(2-3):233-243
In a recent paper, Gutiérrez et al. (Nonlinear Process Geophys 15(1):109–114, 2008) introduced a new characterization of spatiotemporal error growth—the so called mean–variance logarithmic (MVL) diagram—and applied it to study ensemble prediction systems (EPS); in particular, they analyzed single-model ensembles obtained by perturbing the initial conditions. In the present work, the MVL diagram is applied to multi-model ensembles analyzing also the effect of model formulation differences. To this aim, the MVL diagram is systematically applied to the multi-model ensemble produced in the EU-funded DEMETER project. It is shown that the shared building blocks (atmospheric and ocean components) impose similar dynamics among different models and, thus, contribute to poorly sampling the model formulation uncertainty. This dynamical similarity should be taken into account, at least as a pre-screening process, before applying any objective weighting method. 相似文献
146.
Loreto Antón Alfonso Muñoz-Martin Gerardo De Vicente 《Central European Journal of Geosciences》2010,2(2):152-164
The study of intraplate tectonics is crucial for understanding the deformation within plates, far from active plate boundaries and associated stress transmission to the plate interiors. This paper examines the tectonic evolution of the Variscan basement at the western margin of the Cenozoic Duero basin. Located east of the Vilariça Fault System in NW Iberia, this intraplate zone is a relatively flat but elevated area with an intense NNE-SSW trending fault system and associated moderate seismicity. Although the area has played an important role in the Duero basin configuration, its Alpine to present-day tectonic evolution has not been well constrained. In order to characterize the successive paleostress fields, 1428 pairs of fault-striae were measured at 56 sites and two focal mechanisms were used. Stress inversion methods have been applied to analyze paleostress regimes. Results show the existence of three dominant maximum horizontal stress (Shmax) trends: N-S, NE-SW and E-W. Relative and absolute dating of the activated faults for each Shmax shows that the clearly predominant N-S paleostress field in the zone has been active since the Oligocene up to the present day; while a NE-SW stress field is found to have been active during the Cretaceous and an older E-W paleostress field was active in the earlier Alpine cycle (Late Triassic). 相似文献
147.
Zulema Varela J. A. Fernández J. R. Aboal C. Real A. Carballeira 《Journal of Atmospheric Chemistry》2010,65(1):37-48
The aim of the present study was to determine the optimal size of the sampling area that should be used in the moss biomonitoring
technique, in relation to the spatial variation in the concentrations of contaminants determined in samples collected within
short distances (<30 m). For this, the spatial structure in the concentrations of various metals and metalloids was explored
by use of semivariograms calculated by use of a robust estimator of the variance. In each of the 3 sampling sites considered
in the study (one sampled on two occasions), 50 samples of the moss Pseudoscleropodium purum were collected and the tissue concentrations of As, Cd, Cu, Hg, K, Ni, Pb, Se and Zn were determined. The results obtained
show that in most cases (25 out of 32), there was no spatial structure in the concentrations of the elements and that the
semivariograms were subject to the nugget effect. For those elements for which spatial independence or a linear spatial structure
was observed, the size of the sampling area did not affect the results, and the dimensions were irrelevant within the range
studied. The existence of spatial structure, which can be fitted to a spherical model, enabled a range of autocorrelation
to be defined, which corresponded to an area of diameter >16 m. The proposed method must be applied to other species and in
other regions, in order to standardize the size of the sampling sites in the moss biomonitoring technique. 相似文献
148.
Antonio Pedrera Jesús Galindo‐Zaldívar Antonio Ruiz‐Bustos José Rodríguez‐Fernández Ana Ruiz‐Constán 《第四纪科学杂志》2009,24(6):581-592
The NW–SE shortening between the African and the Eurasian plates is accommodated in the eastern Betic Cordillera along a broad area that includes large N‐vergent folds and kilometric NE–SW sinistral faults with related seismicity. We have selected the best exposed small‐scale tectonic structures located in the western Huércal‐Overa Basin (Betic Cordillera) to discuss the seismotectonic implications of such structures usually developed in seismogenic zones. Subvertical ESE–WNW pure dextral faults and E–W to ENE–ESW dextral‐reverse faults and folds deform the Quaternary sediments. The La Molata structure is the most impressive example, including dextral ESE–WNW Neogene faults, active southward‐dipping reverse faults and associated ENE–WSW folds. A molar M1 assigned to Mimomys savini allows for precise dating of the folded sediments (0.95–0.83 Ma). Strain rates calculated across this structure give ~0.006 mm a?1 horizontal shortening from the Middle Pleistocene up until now. The widespread active deformations on small‐scale structures contribute to elastic energy dissipation around the large seismogenic zones of the eastern Betics, decreasing the seismic hazard of major fault zones. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
149.
A modified multiple tension upward infiltration method to estimate the soil hydraulic properties
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Determination of saturated hydraulic conductivity, Ks, and the shape parameters α and n of the water retention curve, θ(h), is of paramount importance to characterize the water flow in the vadose zone. This work presents a modified upward infiltration method to estimate Ks, α and n from numerical inverse analysis of the measured cumulative upward infiltration (CUI) at multiple constant tension lower boundary conditions. Using the HYDRUS‐2D software, a theoretical analysis on a synthetic loam soil under different soil tensions (0, 0–10, 0–50 and 0–100 cm), with and without an overpressure step of 10 cm high from the top boundary condition at the end of the upward infiltration process, was performed to check the uniqueness and the accuracy of the solutions. Using a tension sorptivimeter device, the method was validated in a laboratory experiment on five different soils: a coarse and a fine sand, and a 1‐mm sieved loam, clay loam and silt‐gypseous soils. The estimated α and n parameters were compared to the corresponding values measured with the TDR‐pressure cell method. The theoretical analysis demonstrates that Ks and θ(h) can be simultaneously estimated from measured upward cumulative infiltration when high (>50 cm) soil tensions are initially applied at the lower boundary. Alternatively, satisfactory results can be also obtained when medium tensions (<50 cm) and the Ks calculated from the overpressure step at the end of the experiment are considered. A consistent relationship was found between the α (R2 = 0.86, p < 0.02) and n (R2 = 0.97, p < 0.001) values measured with the TDR‐pressure cell and the corresponding values estimated with the tension sorptivimeter. The error between the α (in logarithm scale) and n values estimated with the inverse analysis and the corresponding values measured with pressure chamber were 3.1 and 6.1%, respectively. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
150.