全文获取类型
收费全文 | 700篇 |
免费 | 61篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 36篇 |
大气科学 | 52篇 |
地球物理 | 185篇 |
地质学 | 268篇 |
海洋学 | 73篇 |
天文学 | 74篇 |
综合类 | 2篇 |
自然地理 | 83篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 21篇 |
2020年 | 18篇 |
2019年 | 25篇 |
2018年 | 30篇 |
2017年 | 28篇 |
2016年 | 34篇 |
2015年 | 27篇 |
2014年 | 40篇 |
2013年 | 69篇 |
2012年 | 37篇 |
2011年 | 30篇 |
2010年 | 29篇 |
2009年 | 39篇 |
2008年 | 31篇 |
2007年 | 36篇 |
2006年 | 24篇 |
2005年 | 25篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 17篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 10篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1967年 | 2篇 |
1966年 | 3篇 |
排序方式: 共有773条查询结果,搜索用时 281 毫秒
761.
Enrico Pirotta Barbara Eva Laesser Andrea Hardaker Nicholas Riddoch Marianne Marcoux David Lusseau 《Marine pollution bulletin》2013
The exponential growth of the human population and its increasing industrial development often involve large scale modifications of the environment. In the marine context, coastal urbanisation and harbour expansion to accommodate the rising levels of shipping and offshore energy exploitation require dredging to modify the shoreline and sea floor. While the consequences of dredging on invertebrates and fish are relatively well documented, no study has robustly tested the effects on large marine vertebrates. We monitored the attendance of common bottlenose dolphins (Tursiops truncatus) to a recently established urbanised foraging patch, Aberdeen harbour (Scotland), and modelled the effect of dredging operations on site usage. We found that higher intensities of dredging caused the dolphins to spend less time in the harbour, despite high baseline levels of disturbance and the importance of the area as a foraging patch. 相似文献
762.
Abstract Hydrological data may be temporally autocorrelated requiring autoregressive process parameters to be estimated. Current statistical methods for hydrological change detection in paired watershed studies rely on prediction intervals, but the current form of prediction intervals does not include all appropriate sources of variation. Corrected prediction intervals for the analysis of paired watershed study data that include variation associated with covariance and linear model parameter estimation are presented. We provide an example of their application to data from the Hinkle Creek Paired Watershed Study located in the western Cascade foothills of Southern Oregon, USA. Research implications of using the correct prediction limits and incorporating the estimation uncertainty of autoregressive process parameters are discussed. Editor D. Koutsoyiannis Citation Som, N.A., Zégre, N.P., Ganio, L.M. and Skaugset, A.E., 2012. Corrected prediction intervals for change detection in paired watershed studies. Hydrological Sciences Journal, 57 (1), 134–143. 相似文献
763.
Nicholas Culshaw Emilia Mosonyi Peter Reynolds 《International Journal of Earth Sciences》2012,101(1):291-306
The Rodna Mountains afford the most internal structural window into the crystalline units of the Eastern Carpathians in Romania.
The Rodna Mountains consist of Variscan metamorphic nappes that were restacked in the Alpine phase of Carpathian development
forming the Subbucovinian and Infrabucovinian nappes. In order to evaluate age of deformation, ten samples were taken from
the zone of greenschist facies mylonitic schist that marks the Alpine tectonic boundary between the Subbucovinian and Infrabucovinian
nappes and 40Ar/39Ar laser single-grain ages determined for schistosity-forming muscovite. Microstructural assessment of quartz and muscovite
distinguished two deformation events. Single-grain ages from the microstructurally most strongly reworked samples (four samples)
give a tight clustering of ages at ca. 95 Ma. The least reworked schists have a broader clustering of ages spanning ca. 200–280 Ma
with a late Permian peak and some samples showing outlier ages in the range 200–100 Ma. The relative development of the outliers,
which correlates with evidence for increased microstructural reworking, is interpreted to mark progressive isotopic resetting.
The ca. 95 Ma ages for the most reworked schists are estimates for the age of the Alpine nappe stacking. The ca. 200–280 Ma
ages are similar to those of magmatism, metamorphism, and sedimentation thought to mark post-Variscan-pre-Alpine rifting and
ocean basin formation in parts of the Alps and may be the thermal imprint of a related event in the Eastern Carpathians. 相似文献
764.
Analytical hydrologic models and the design of policy instruments for groundwater-quality management
This paper explores how analytical hydrologic models can inform the effective design and choice of policy instruments to manage groundwater quality by coupling a social-planner’s problem of optimal groundwater-quality management with analytical solutions from the hydrology literature. A theoretical analysis is performed in order to characterize the properties of an optimal emissions policy. The model is then applied in a numerical analysis of groundwater contamination by chloride from highway deicers, demonstrating the relevance of the theoretical results to practical management settings. This analytical approach can help determine which policy instruments are likely to be effective in controlling groundwater pollution, especially if costly numerical groundwater models are not available for the aquifer in question. Unlike previous economic studies of groundwater contamination, this approach defines optimal emissions policies as a function of geophysical parameters employed by hydrologists such as distance between source and sink, groundwater velocity, and aquifer dispersivity. The theoretical section of this paper also demonstrates that the relationship between geophysical parameters and optimal emissions levels may be ambiguous. 相似文献
765.
Appropriate Uses and Practical Limitations of 2D Numerical Analysis of Tunnels and Tunnel Support Response 总被引:5,自引:3,他引:2
Nicholas Vlachopoulos Mark S. Diederichs 《Geotechnical and Geological Engineering》2014,32(2):469-488
In spite of the gradual development of three-dimensional analysis packages utilizing finite element models or finite difference algorithms for stress–strain calculations, two-dimensional (2D) analysis is still used as the primary engineering tool for practical analysis of tunnel behavior and tunnel support performance for design—particularly at the preliminary stage of a project. The applicability of 2D finite element analysis or analytical convergence confinement solutions to staged support installation depend on the application of an assumed or validated longitudinal displacement profile. Convergence in commonly applied 2D staged models is controlled by boundary displacement or internal pressure relaxation. While there have been developments to improve this methodology, this often assumes independence between the ground reaction curve and the support resistance, independence between the longitudinal displacement profile to support application, and the assumption that non-isotropic stresses and non-circular geometries can be handled in the same way as circular tunnels in isotropic conditions. This paper examines the validity of these assumptions and the error inherent in these extensions to 2D tunnel analysis. Anisotropic stresses and lagged (staged) excavation present a particular problem. Practical solutions are proposed for support longitudinal displacement LDPs in simplified conditions. 相似文献
766.
Coralie?SiégelEmail author Nicholas?Arndt Stephen?Barnes Anne-Laure?Henriot Pierre?Haenecour Vinciane?Debaille Nadine?Mattielli 《Contributions to Mineralogy and Petrology》2014,168(6):1084
Two Archaean komatiitic flows, Fred’s Flow in Canada and the Murphy Well Flow in Australia, have similar thicknesses (120 and 160 m) but very different compositions and internal structures. Their contrasting differentiation profiles are keys to determine the cooling and crystallization mechanisms that operated during the eruption of Archaean ultramafic lavas. Fred’s Flow is the type example of a thick komatiitic basalt flow. It is strongly differentiated and consists of a succession of layers with contrasting textures and compositions. The layering is readily explained by the accumulation of olivine and pyroxene in a lower cumulate layer and by evolution of the liquid composition during downward growth of spinifex-textured rocks within the upper crust. The magmas that erupted to form Fred’s Flow had variable compositions, ranging from 12 to 20 wt% MgO, and phenocryst contents from 0 to 20 vol%. The flow was emplaced by two pulses. A first ~20-m-thick pulse was followed by another more voluminous but less magnesian pulse that inflated the flow to its present 120 m thickness. Following the second pulse, the flow crystallized in a closed system and differentiated into cumulates containing 30–38 wt% MgO and a residual gabbroic layer with only 6 wt% MgO. The Murphy Well Flow, in contrast, has a remarkably uniform composition throughout. It comprises a 20-m-thick upper layer of fine-grained dendritic olivine and 2–5 vol% amygdales, a 110–120 m intermediate layer of olivine porphyry and a 20–30 m basal layer of olivine orthocumulate. Throughout the flow, MgO contents vary little, from only 30 to 33 wt%, except for the slightly more magnesian basal layer (38–40 wt%). The uniform composition of the flow and dendritic olivine habits in the upper 20 m point to rapid cooling of a highly magnesian liquid with a composition like that of the bulk of the flow. Under equilibrium conditions, this liquid should have crystallized olivine with the composition Fo94.9, but the most magnesian composition measured by electron microprobe in samples from the flow is Fo92.9. To explain these features, we propose that the parental liquid contained around 32 wt% MgO and 3 wt% H2O. This liquid degassed during the eruption, creating a supercooled liquid that solidified quickly and crystallized olivine with non-equilibrium textures and compositions. 相似文献
767.
Prey availability and feeding success affect survival of larval striped bass (Morone saxatilis) in Chesapeake Bay and contribute to the >30-fold interannual recruitment variability. Gut contents and stable isotope analyses (δ15N and δ13C) were conducted on striped bass larvae to evaluate sources of nutrition in 2007 and 2008, years of high and poor recruitment, respectively. Ichthyoplankton and zooplankton were surveyed in the upper Chesapeake Bay, in proximity to the estuarine turbidity maximum and associated salt front. Feeding incidence and numbers of prey per gut were similar in both years and varied in relation to the salt front. The primary prey in each year was the estuarine copepod Eurytemora affinis. Substantial consumption of the freshwater cladoceran Bosmina spp. also occurred, especially up-estuary of the salt front in 2007, demonstrating that secondary prey are important to larval diets in some years. Stable isotope analysis of yolk sac and feeding-stage larvae of striped bass revealed an ontogenetic shift from maternal stable isotope signatures to those indicative of prey source. Feeding-stage larvae from up-estuary locations had the most negative δ13C values, indicating a relatively high terrestrial carbon source in prey. Spatio-temporal variability in δ15N signatures of larvae followed similar trends of δ15N variability in zooplankton prey with the highest δ15N values up-estuary of the salt front and estuarine turbidity maximum. A stable isotope analysis on archived striped bass larvae collected in 1998 and 2003, years of moderate and high recruitment, respectively, expanded the documented range of isotope signatures but did not clearly distinguish effects of nutritional sources on recruitment. 相似文献
768.
Nicholas J. Nidzieko Joseph A. Needoba Stephen G. Monismith Kenneth S. Johnson 《Estuaries and Coasts》2014,37(1):91-110
Optical in situ chemical sensors enable sampling intervals and durations that rival acoustic techniques used for measuring currents. Coupling these high-frequency biogeochemical and physical measurements in estuaries to address ecosystem-scale questions, however, is still comparatively novel. This study investigated how tides affect ecosystem metabolism in a mesotidal estuary in central California (Elkhorn Slough). Dissolved oxygen measurements were used to estimate the terms in a control volume budget for a tidal creek/marsh complex at tidal timescales over several weeks. Respiration rates were 1.6 to 7.3 g O2 m?2 day?1; net community production approached 20 g O2 m?2 day?1. We found that aquatic NCP integrated throughout the creek complex varied significantly over the spring-neap cycle. The intertidal contribution to aquatic metabolism was net heterotrophic during spring tides and generally in balance during neap tides because spring-tide marsh inundation was limited to nighttime, and therefore the marsh could not contribute any primary production to the water column. At the estuary scale, the fortnightly export of oxygen from the main channel to the intertidal was largely balanced by an advective flux up-estuary. 相似文献
769.
Shaun Cole Will J. Percival John A. Peacock Peder Norberg Carlton M. Baugh Carlos S. Frenk Ivan Baldry Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Nicholas J. G. Cross Gavin Dalton Vincent R. Eke Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Karl Glazebrook Carole Jackson Adrian Jenkins Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2005,362(2):505-534
770.
The potential for western mosquitofish, Gambusia affinis, to negatively affect populations of black mudfish in New Zealand wetlands was investigated with annual fishing surveys of the Whangamarino wetland and by laboratory experiments evaluating competition and predation of mosquitofish on mudfish adults and larvae. Abundance of mudfish juveniles was reduced in the presence of mosquitofish at marginal wetland sites close to permanent water, but mosquitofish were not found at ephemeral adult mudfish habitats. In constructed wetland microcosms, mosquitofish reduced both growth and condition of post‐larval mudfish but did not attack or kill mudfish. In laboratory aquaria, mosquitofish rapidly consumed mudfish fry but survival time of the latter was significantly extended by an increase in density of submerged structures and by the presence of an alternative food source for mosquitofish. Because mosquitofish cannot survive in ephemeral wetlands that dry over summer, the impacts of mosquitofish on mudfish are likely to be minimal except in habitats where mosquitofish can survive year‐round owing to the presence of permanent standing water. 相似文献