全文获取类型
收费全文 | 237篇 |
免费 | 7篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 44篇 |
地球物理 | 45篇 |
地质学 | 87篇 |
海洋学 | 23篇 |
天文学 | 26篇 |
自然地理 | 17篇 |
出版年
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 20篇 |
2013年 | 12篇 |
2012年 | 4篇 |
2011年 | 15篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 18篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有249条查询结果,搜索用时 62 毫秒
81.
Future projections of temperature-related climate change impacts on the railway network of Great Britain 总被引:1,自引:0,他引:1
Erika J. Palin Hazel E. Thornton Camilla T. Mathison Rachel E. McCarthy Robin T. Clark John Dora 《Climatic change》2013,120(1-2):71-93
Great Britain’s main line railway network is known to experience various temperature-related impacts, e.g. track buckling and overhead power line sag at high ambient temperatures. Climate change could alter the frequency of occurrence of these impacts. We have therefore investigated the climate change impact on various temperature-related issues, identified during workshops with rail industry specialists, using a perturbed physics ensemble (PPE) of the Met Office’s regional climate model (RCM), HadRM3. We have developed novel approaches to combine RCM data with railway industry knowledge, typically by identifying key meteorological thresholds of interest and analysing exceedance of these out to the 2040s. We performed a statistical analysis of the projected changes for each issue, via bootstrapping of the unperturbed PPE member. Although neither the PPE nor the bootstrapping analysis samples the full range of uncertainty in the projections, they nonetheless provide complementary perspectives on the suitability of the projections for use in decision-making. Our main findings include projected increases in the summertime occurrence of temperature conditions associated with (i) track buckling, (ii) overhead power line sag, (iii) exposure of outdoor workers to heat stress, and (iv) heat-related delays to track maintenance; and (v) projected decreases in the wintertime occurrence of temperatures conditions associated with freight train failure owing to brake problems. For (i), the statistical significance varied with track condition and location; for (ii) and (iii), with location; and for (iv) and (v), projected changes were significant across Great Britain. As well as assessing the changes in climate-related hazard, information about the vulnerability of the network to past temperature-related incidents has been summarised. Combining the hazard and vulnerability elements will eventually support a climate risk assessment for the industry. 相似文献
82.
Isabel Márquez Josefa Masegosa Mariano Moles Jesús Varela Daniella Bettoni Giusseppe Galletta 《Astrophysics and Space Science》2003,284(2):711-714
We present the study of long slit spectra in the region ofHα emission line of a sample of 111 spiral galaxies with recognizable
and well defined spiral morphology and with a well determined environmental status, ranging from isolation to non-disruptive
interaction with satellites or companions. The form and properties of the rotation curves (RC) are considered as a function
of the isolation degree, morphological type, t, and luminosity. The line ratios are used to estimate the metallicity of all
the detected HII regions, thus producing a composite metallicity profile for different types of spirals. We have found that
isolated galaxies (ISO) tend to be of later types and lower luminosity than the interacting galaxies (INT). The outer parts
of the RC of ISO tend to be flatter than in INT, but they show similar relations between global parameters. The scatter of
the Tully-Fisher (TF) relation defined by ISO is significantly lower than that of INT. The [NII]/Hα ratios, used as a metallicity
indicator, show a clear trend between Z and t, with earlier spirals showing higher ratios; this trend is tighter when instead
of t the gradient of the inner RC, G, is used; no trend is found with the change in interaction status. The Z-gradient of
the disks depends on the type, being almost flat for early spirals, and increasing for later types. The [NII]/Hα ratios measured
for disk HII regions of INT are higher than for normal/ISO objects, even if all the galaxy families present similar distributions
of Hα Equivalent Width.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
83.
Theoretical arguments point to and recent observations confirm the existence of clouds in Titan's atmosphere, yet we possess very little data on their particle size, composition and formation mechanism. A time-dependent microphysical model is used to study the evolution of ice clouds in Titan's atmosphere. The model simulates nucleation, condensational growth, evaporation, coagulation, and transport of particles in a column of atmosphere. A variety of cloud compositions are studied, including pure ethane clouds, pure methane clouds, and mixed methane-ethane clouds (all with tholin cores). The abundance of methane cloud particles may be limited by the number of ethane coated tholin nuclei rather than the number of tholins with hydrocarbon coatings. However, even the condensation of methane onto these relatively sparse ethane/tholin cloud particles is sufficient to keep the methane close to saturation. Typical methane supersaturations are of order 0.06 on the average. For simulations which take into account recent lab measurements indicating it is relatively easy for methane to nucleate onto tholin particles without an ethane-layer present, the three types of clouds (methane, ethane, and mixed) exist simultaneously. Pure methane clouds are the most abundant cloud type and serve to lower the supersaturation to about 0.04. Cloud production does not require a continuous surface source of methane. However, clouds produced by mean motions are not the visible methane clouds seen in recent Cassini and ground-based observations. Ethane clouds in the troposphere almost instantaneously nucleate methane to form mixed clouds. However, a thin ethane ‘haze’ remains just above the tropopause for some scenarios and the mixed clouds at the tropopause remain ?50% ethane by mass. Also, evaporation of methane from the mixed cloud particles near the surface leaves a thicker layer of ethane cloud particles at ∼10 km. Nevertheless, the precipitation rate of methane to Titan's surface is between 0.001 and 0.5 cm/terrestrial-year, depending on various initial conditions such as critical saturation, size and abundance of cloud condensation nuclei, surface sources and eddy diffusion. 相似文献
84.
Shay L.K. Cook T.M. Peters H. Mariano A.J. Weisberg R. An P.E. Soloviev A. Luther M. 《Oceanic Engineering, IEEE Journal of》2002,27(2):155-169
An ocean surface current radar (OSCR) in the very high frequency (VHF) mode was deployed in South Florida Ocean Measurement Center (SFOMC) during the summer of 1999. During this period, a 29-d continuous time series of vector surface currents was acquired starting on 9 July 1999 and ending 7 August 1999. Over a 20-min sample interval, the VHF radar mapped coastal ocean currents over a 7.5 km × 8 km domain with a horizontal resolution of 250 m at 700 grid points. A total of 2078 snapshots of the two-dimensional current vectors were acquired during this time series and of these samples, only 69 samples (3.3%) were missing from the time series. During this period, complex surface circulation patterns were observed that included coherent, submesoscale vortices with diameters of 2 to 3 km inshore of the Florida Current. Comparisons to subsurface measurements from moored and ship-board acoustic Doppler current profiles revealed regression slopes of close to unity with biases ranging from 4 to 8 cm s-1 between surface and subsurface measurements at 3 to 4 m beneath the surface. Correlation coefficients were 0.8 or above with phases of - 10 to - 20° suggestive of an anticyclonic veering of current with depth relative to the surface current. The radar-derived surface current field provided spatial context for an observational network using mooring-, ship- and autonomous underwater vehicle-sensor packages that were deployed at the SFOMC 相似文献
85.
Jessica L. Nagel Hilary A. Neckles Glenn R. Guntenspergen Erika N. Rocks Donald R. SchoolmasterJr James B. Grace Dennis Skidds Sara Stevens 《Estuaries and Coasts》2018,41(2):334-348
Tools for assessing and communicating salt marsh condition are essential to guide decisions aimed at maintaining or restoring ecosystem integrity and services. Multimetric indices (MMIs) are increasingly used to provide integrated assessments of ecosystem condition. We employed a theory-based approach that considers the multivariate relationship of metrics with human disturbance to construct a salt marsh MMI for five National Parks in the northeastern USA. We quantified the degree of human disturbance for each marsh using the first principal component score from a principal components analysis of physical, chemical, and land use stressors. We then applied a metric selection algorithm to different combinations of about 45 vegetation and nekton metrics (e.g., species abundance, species richness, and ecological and functional classifications) derived from multi-year monitoring data. While MMIs derived from nekton or vegetation metrics alone were strongly correlated with human disturbance (r values from ?0.80 to ?0.93), an MMI derived from both vegetation and nekton metrics yielded an exceptionally strong correlation with disturbance (r = ?0.96). Individual MMIs included from one to five metrics. The metric-assembly algorithm yielded parsimonious MMIs that exhibit the greatest possible correlations with disturbance in a way that is objective, efficient, and reproducible. 相似文献
86.
Rock Glaciers in the Patagonian Andes: An Inventory for the Monte San Lorenzo (Cerro Cochrane) Massif, 47° S
下载免费PDF全文
![点击此处可从《Geografiska Annaler: Series A, Physical Geography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Daniel Falaschi Takeo Tadono Mariano Masiokas 《Geografiska Annaler: Series A, Physical Geography》2015,97(4):769-777
Although rock glaciers in the Central and Desert Andes of Argentina and Chile have been previously studied in detail, much less attention has been paid to the occurrence of these permafrost forms in Patagonia. Recently, however, the establishment of the Argentinean Glacier Inventory program, which intends to inventory and monitor all ice masses along the Argentinean Andes, has started a large amount of new geocryological research. The project is designed to provide reliable and worldwide comparable results, supported by well established technical procedures and background information. Presented here is the first rock glacier inventory of the Monte San Lorenzo (Cerro Cochrane) region in the southern Patagonian Andes. A total of 130 intact (9.86 km2) and 47 fossil (1.45 km2) landforms were inventoried using two 2.5 m resolution ALOS Panchromatic Remote‐sensing Instruments for Stereo Mapping images. Since the Argentinean federal initiative described above legally protects all rock glaciers in the country as water reserves, and due to the little scientific knowledge concerning rock glaciers in the vast majority of the Patagonian Andes, this inventory provides an important basis for political decision‐making and opens further geocryological research avenues for the Patagonian region in general. 相似文献
87.
Sabine Hahn Erika Griesshaber Wolfgang W. Schmahl Rolf D. Neuser Ann‐Christine Ritter Rene Hoffmann Dieter Buhl Andrea Niedermayr Anna Geske Adrian Immenhauser 《Sedimentology》2014,61(6):1625-1658
Throughout much of Earth's history, marine carbonates have represented one of the most important geological archives of environmental change. Several pivotal events during the Phanerozoic, such as mass extinctions or hyperthermal events have recently been associated with ocean acidification. Nevertheless, well‐defined geological proxies for past ocean acidification events are, at best, scarce. Here, experimental work explores the response of bivalve shell ultrastructure and isotope geochemistry (δ13C, δ18O and δ26Mg) to stressful environments, in particular to sea water acidification. In this study, the common blue mussel, Mytilus edulis, was cultured (from early juvenile stages to one year of age) at four pH regimes (pHNBS 7·2 to pH 8·0). Shell growth rate and ultrastructure of mainly the calcitic portion of the shells were compared between experimental treatments. Specimens exposed to low‐pH environments show patches of disordered calcitic fibre orientation in otherwise well‐structured shells. Furthermore, the electron backscattered diffraction analyses reveal that, under acidified conditions, the c‐axis of the calcite prisms exhibits a bimodal or multi‐modal distribution pattern. Similar shell disorder patterns have been reported from mytilids kept under naturally acidified sea water conditions. In contrast, this study found no evidence that different pH regimes affect shell carbon, oxygen or magnesium isotope ratios. Based on these observations, it is proposed that: (i) stressful environments, in this case low sea water pH, predictably affect bivalve biomineralization patterns; and (ii) these findings bear potential as a novel (petrographic) proxy for ancient sea water acidification. An assessment of the applicability of these data to well‐preserved fossil shell material from selected time intervals requires additional work. 相似文献
88.
89.
90.
Mariano Bonomo Alejandro Fabián Zucol Beatriz Gutiérrez Téllez Andrea Coradeghini María Susana Vigna 《Journal of Paleolimnology》2009,41(2):273-296
This paper presents results of interdisciplinary palaeoenvironmental research carried out on a sediment sequence from the
Nutria Mansa 1 archaeological site. This late Holocene site is located in the Pampean plains, Argentina. Siliceous microfossils
were recorded (i.e. phytoliths, diatoms, chrysophytes, sponges) and micro-charcoal was analyzed. In addition, fauna identified
at the site were correlated with regional palaeoclimatic evidence. Based on the microfossil associations, we concluded that
the human occupations occurred beside a fluvial and brackish-freshwater lacustrine setting. Grass communities were located
on its margins that developed under a warm temperate climate with evidence for dryness and marked seasonality in part of the
record. Although some stratigraphic and faunal evidence indicates a possible temperature increase, these fluctuations were
not sufficient to extirpate mammals of arid and cold environments. 相似文献