全文获取类型
收费全文 | 362篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 19篇 |
地球物理 | 102篇 |
地质学 | 103篇 |
海洋学 | 31篇 |
天文学 | 55篇 |
综合类 | 1篇 |
自然地理 | 66篇 |
出版年
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 18篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 19篇 |
2012年 | 10篇 |
2011年 | 21篇 |
2010年 | 20篇 |
2009年 | 31篇 |
2008年 | 20篇 |
2007年 | 20篇 |
2006年 | 18篇 |
2005年 | 10篇 |
2004年 | 12篇 |
2003年 | 14篇 |
2002年 | 7篇 |
2001年 | 15篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1933年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有384条查询结果,搜索用时 30 毫秒
141.
A comparison of seismic risk maps for Italy 总被引:5,自引:3,他引:2
Helen Crowley Miriam Colombi Barbara Borzi Marta Faravelli Mauro Onida Manuel Lopez Diego Polli Fabrizio Meroni Rui Pinho 《Bulletin of Earthquake Engineering》2009,7(1):149-180
National seismic risk maps are an important risk mitigation tool as they can be used for the prioritization of regions within
a country where retrofitting of the building stock or other risk mitigation measures should take place. The production of
a seismic risk map involves the convolution of seismic hazard data, vulnerability predictions for the building stock and exposure
data. The seismic risk maps produced in Italy over the past 10 years are compared in this paper with recent proposals for
seismic risk maps based on state-of-the-art seismic hazard data and mechanics-based vulnerability assessment procedures. The
aim of the paper is to open the discussion for the way in which future seismic risk maps could be produced, making use of
the most up-to-date information in the fields of seismic hazard evaluation and vulnerability assessment. 相似文献
142.
Lynda C. Howard Paul J. Wood Malcolm T. Greenwood Helen M. Rendell 《Journal of Paleolimnology》2009,42(4):453-466
Sub-fossil insect remains have the potential to characterise changing environmental conditions in both lentic and lotic water
systems, however, relatively few studies have been undertaken in riverine environments. This paper uses sub-fossil caddisfly
larvae (Trichoptera) and aquatic beetles (Coleoptera) to reconstruct river flow conditions for a large paleochannel (from
multiple monoliths) using the Lotic invertebrate Index for Flow Evaluation (LIFE). Examination of the larval Trichoptera and
Coleoptera remains indicated a marked change in the community and flow environment, as suggested by paleoLIFE scores within
the profile of three of the monoliths examined. At the base of the channel the community was characterised by taxa indicative
of high energy lotic habitats with predominantly mineral substrates (e.g. Trichoptera: Hydropsyche
contubernalis and Brachycentrus
subnubilis, Coleoptera: Elmis
aenea and Esolus
parallelepipedus). Within three of the monoliths there was a change in community composition to one indicative of a low energy backwater/lentic
environment with abundant submerged and emergent vegetation (e.g. Trichoptera: Phryganea
bipunctata and Limnephilus
flavicornis, Coleoptera: Colymbetes
fuscus and Hydrobius
fuscipes). Detrended Correspondence Analysis (DCA) and loss of mass on ignition (LOI) indicated the presence of a strong environmental
gradient within the data, associated with river flow. The utilisation of two aquatic insect orders provides clear evidence
of temporal changes within the instream community and when combined with knowledge of ecological and habitat associations,
allows differences between the two groups to be interpreted more clearly. 相似文献
143.
Development and assessment of damage‐to‐loss models for moment‐frame reinforced concrete buildings
下载免费PDF全文
![点击此处可从《地震工程与结构动力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Luís Martins Vítor Silva Mário Marques Helen Crowley Raimundo Delgado 《地震工程与结构动力学》2016,45(5):797-817
The assessment of earthquake loss often requires the definition of a relation between a measure of damage and a quantity of loss, usually achieved through the employment of a damage‐to‐loss model. These models are frequently characterized by a large variability, which inevitably increases the uncertainty in the vulnerability assessment and earthquake loss estimation. This study provides an insight on the development of damage‐to‐loss functions for moment‐frame reinforced concrete buildings through an analytical methodology. Tri‐dimensional finite element models of existing reinforced concrete buildings were subjected to a number of ground motion records compatible with the seismicity in the region of interest, through nonlinear dynamic analysis. These results were used to assess, for a number of damage states, the probability distribution of loss ratio, taking into consideration member damage and different repair techniques, as well as to derive sets of fragility functions. Then, a vulnerability model (in terms of the ratio of cost of repair to cost of replacement, conditional on the level of ground shaking intensity) was derived and compared with the vulnerability functions obtained through the combination of various damage‐to‐loss models with the set of fragility functions developed herein. In order to provide realistic estimates of economic losses due to seismic action, a comprehensive study on repair costs using current Portuguese market values was also carried out. The results of this study highlight important issues in the derivation of vulnerability functions, which are a fundamental component for an adequate seismic risk assessment. © 2015 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd. 相似文献
144.
Helen M. Roe G. Russell Coope Robert J.N. Devoy Colin J.O. Harrison Kirsty E.H. Penkman Richard C. Preece Danielle C. Schreve 《Quaternary Science Reviews》2009,28(23-24):2342-2373
Multidisciplinary investigations of the vegetational, faunal and sea-level history inferred from the infills of buried channels on the coast of eastern Essex have a direct bearing on the differentiation of MIS 11 and MIS 9 in continental records. New data are presented from Cudmore Grove, an important site on Mersea Island that can be linked to the terrace sequence of the River Thames. The vegetational history has been reconstructed from a pollen sequence covering much of the interglacial represented. The temperate nature of the climate is apparent from a range of fossil groups, including plant remains, vertebrates (especially the rich herpetofauna), molluscs and beetles, which all have strong thermophilous components. The beetle data have been used to derive a Mutual Climatic Range reconstruction, suggesting that mean July temperatures were about 2 °C warmer than modern values for southeast England, whereas mean January temperatures may have been slightly colder. The sea-level history has been reconstructed from the molluscs, ostracods and especially the diatoms, which indicate that the marine transgression occurred considerably earlier in the interglacial cycle than at the neighbouring Hoxnian site at Clacton. There are a number of palynological similarities between the sequence at Cudmore Grove and Clacton, especially the presence of Abies and the occurrence of Azolla filiculoides megaspores. Moreover, both sites have yielded Palaeolithic archaeology, indeed the latter is the type site of the Clactonian (flake-and-core) industry. However, the sites can be differentiated on the basis of mammalian biostratigraphy, new aminostratigraphic data, as well as the differences in the sea-level history. The combined evidence suggests that the infill of the channel at Cudmore Grove accumulated during MIS 9, whereas the deposits at Clacton formed during MIS 11. The infill of a much later channel, yielding non-marine molluscs and vertebrates including Hippopotamus, appears to have formed during the Ipswichian (MIS 5e). This evidence is compared with other important sites of late Middle Pleistocene age in Britain and elsewhere on the continent and the importance of a multidisciplinary approach is stressed. 相似文献
145.
The Pacific island nation-state of Tuvalu featured significantly at the Copenhagen Conference of Parties (COP) 15 climate change negotiations, where the vulnerability of Tuvalu to sea level rise and emotional outpourings of the Tuvaluan delegation contributed to the nation's prominence. In this paper we discuss the likely impacts for Tuvalu of a 1.5°C versus 2°C global warming target and explore sadness and discomfort surrounding discussion of these targets during COP 15. We highlight tensions between science and emotion, arguing that affective encounters can be significant in climate change decision-making. Weeping by a member of the Tuvalu delegation evoked discomfort in the conference plenary. This discomfort briefly unsettled the apparently stable boundaries of convention and protocol that seek to separate emotion from science and politics. We argue that possibilities for change arise when emotions enter climate change negotiations, even though (or perhaps because) these are arenas that privilege rational exchange. Our conclusion urges that more attention be paid to how climate science and emotion are intertwined in climate change politics. 相似文献
146.
Deformation-related microstructures in magmatic zircon and implications for diffusion 总被引:1,自引:1,他引:0
Steven Michael Reddy Nicholas E. Timms Patrick Joseph Hamilton Helen R. Smyth 《Contributions to Mineralogy and Petrology》2009,157(2):231-244
An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole
glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation.
A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous
zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron
backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of
up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic
bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations
are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD
maps. Less common <100> misorientation axes account for minor components of crystallographic dispersion. These observations
are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with
the operation of <001>{100} and <100>{010} slip systems. The restriction of deformation microstructures to large glomerocrysts
and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon
grains, indicate that zircon deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior
to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic
stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain
deformation of the cumulate in the late stages of initial crystallisation. These results provide the first evidence of crystal
plastic dislocation creep in zircon associated with magmatic crystallisation and indicate that the development of crystal-plastic
microstructures in zircon is not restricted to high-strain rocks. Such microstructures have previously been shown to enhance
bulk diffusion of trace elements (U, Th and REE) in zircon. The development of deformation microstructures, and therefore
multiple diffusion pathways in zircon in the magmatic environment, has significant implications for the interpretation of
geochemical data from igneous zircon and the trace element budgets of melts due to the potential enhancement of bulk diffusion
and dissolution rates. 相似文献
147.
Roberto Soria Kinwah Wu Helen M. Johnston 《Monthly notices of the Royal Astronomical Society》1999,310(1):71-77
We carried out spectroscopic observations of the candidate black hole binary GX 339−4 during its low–hard and high–soft X-ray states. We have found that the spectrum is dominated by emission lines of neutral elements with asymmetric, round-topped profiles in the low–hard state. In the high–soft state, however, the emission lines from both neutral and ionized elements have unambiguously resolved double-peaked profiles. The detection of double-peaked emission lines in the high–soft state, with a larger peak separation for higher ionization lines, indicates the presence of an irradiatively heated accretion disc. The round-topped lines in the low–hard state are probably caused by a dense matter outflow from an inflated non-Keplerian accretion disc. Our data do not show velocity modulations of the line centres caused by the orbital motion of the compact object, neither do the line basewidths show substantial variations in each observational epoch. There are no detectable absorption lines from the companion star. All these features are consistent with those of a system with a low-mass companion star and low orbital inclination. 相似文献
148.
Ezer Tal Carniel Sandro Amin Chabchoub de Camargo Ricardo Estrada-Allis Sheila N. Gao Guoping Greatbatch Richard J. Lermusiaux Pierre F. J. Liu Zhiyu Miyazawa Yasumasa Forster Alejandro Orfila Panickal Swapna Phillips Helen Pinones Andrea Stanev Emil Volker Christoph Xu Fanghua Young Emma 《Ocean Dynamics》2023,73(1):35-38
149.
The results of a thermoluminescence (TL) dating and geochemical survey of loessic deposits in southeast England, involving sampling at 26 localities, demonstrate that the loessic deposits appear to be the product of at least three depositional phases of aeolian silt during the Late Pleistocene, namely 10-25 ka BP, 50–125 ka BP and > 170 ka BP. The majority of localities sampled date to the Late Devensian, but isolated pockets of older material were found throughout the area. The majority of the samples analysed were of decalcified material. The results of geochemical analyses of major oxide and trace element concentrations indicate the uniformity of material and suggest a common provenance. 相似文献
150.
Helen J. Fraser † Mark P. Collings Martin R. S. McCoustra David A. Williams 《Monthly notices of the Royal Astronomical Society》2001,327(4):1165-1172
Water (H2 O) ice is an important solid constituent of many astrophysical environments. To comprehend the role of such ices in the chemistry and evolution of dense molecular clouds and comets, it is necessary to understand the freeze-out, potential surface reactivity and desorption mechanisms of such molecular systems. Consequently, there is a real need from within the astronomical modelling community for accurate empirical molecular data pertaining to these processes. Here we give the first results of a laboratory programme to provide such data. Measurements of the thermal desorption of H2 O ice, under interstellar conditions, are presented. For ice deposited under conditions that realistically mimic those in a dense molecular cloud, the thermal desorption of thin films (≪50 molecular layers) is found to occur with zeroth-order kinetics characterized by a surface binding energy, E des , of 5773 ± 60 K, and a pre-exponential factor, A , of 1030 ± 2 molecules cm−2 s−1 . These results imply that, in the dense interstellar medium, thermal desorption of H2 O ice will occur at significantly higher temperatures than has previously been assumed. 相似文献