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251.
Effects of irradiance on benthic and water column processes in a Gulf of Mexico estuary: Pensacola Bay, Florida, USA 总被引:1,自引:0,他引:1
Michael C. Murrell Jed G. Campbell James D. Hagy III Jane M. Caffrey 《Estuarine, Coastal and Shelf Science》2009,81(4):501-512
We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during the summers of 2003 and 2004 on 16 dates distributed along depth and salinity gradients. Dissolved oxygen fluxes were measured on replicate sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH4+, NO3−, PO43−) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis–irradiance model and the parameter estimates were used to calculate daily integrated production in the water column and the benthos. The results suggest that shoal environments supported substantial benthic productivity, averaging 13.6 ± 4.7 mmol O2 m−2 d−1, whereas channel environments supported low benthic productivity, averaging 0.5 ± 0.3 mmol O2 m−2 d−1 (±SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O2 m−2 d−1, comprising about 16–32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O2 m−2 d−1, respectively Inorganic nutrient fluxes were generally low compared to relevant estuarine literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m−2 d−1 for NH4+, 0.58 ± 1.08 mmol m−2 d−1 for NO3−, 0.01 ± 0.09 mmol m−2 d−1 for PO43−. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in shallow estuarine systems. 相似文献
252.
Extreme heat events frequently have adverse effects on population health. Within every population certain groups and individuals are at a greater risk of heat-related morbidity and mortality than others. While certain physiological characteristics (advanced age, chronic conditions, etc.) are known to increase the risk of illness and/or death during periods of extreme heat, the role of social and community level factors in aggravating or mitigating this risk is poorly understood. This paper reviews the literature on the social and community level factors that affect heat-related morbidity and mortality in order to identify shortfalls in current heat health response plans so that new approaches can be recommended. While social isolation, ethnicity, socioeconomic status, and neighborhood characteristics have all been identified as potential factors affecting the risk of heat-related illness and mortality, these are rarely, if ever, identified as heat health research priorities and are thus often neglected in heat emergency planning. Current research and programming practices are often prioritized from the top down where decisions are made at the federal level and research priorities are determined by national research bodies. This, unfortunately, may not allow enough flexibility to meet the needs of physically, socially and culturally diverse communities. A more socio-ecological approach to heat health research and planning would better allow for the identification of community level vulnerabilities and available resources and would encourage communities to work with regional or national partners to adapt response plans accordingly. The development of future plans should involve more partnerships at the community level so that social and community level factors that are currently overlooked may be included in heat health response strategies. 相似文献
253.
Horsburgh Kevin Haigh Ivan D. Williams Jane De Dominicis Michela Wolf Judith Inayatillah Addina Byrne David 《Ocean Dynamics》2021,71(6-7):715-730
Ocean Dynamics - In this paper, we show that over the next few decades, the natural variability of mid-latitude storm systems is likely to be a more important driver of coastal extreme sea levels... 相似文献
254.
255.
The EM12 multibeam echosounder can record acoustic backscatter information as well as high resolution bathymetry. The dataset presented, from the axis of the Mid-Atlantic Ridge at 45° N, was the first EM12 survey of a mid-ocean ridge. This paper presents methods for utilising the backscatter information. Data processing enables the production of a mosaic of acoustic backscatter, and visualisation techniques are investigated to provide initial qualitative views of the combined backscatter and bathymetry datasets. The co-registration of the backscatter and bathymetry data enables quantitative analysis of their relationships. Various sites of different geological type have been selected and their angular acoustic backscattering relationships estimated, including the effect on backscatter of incidence angle, its regional variability with bottom type and the influence of bottom slope. Incidence angles and bottom type are shown to affect backscatter to a similar degree, while slopes appear to contribute little. The geometry of hull-mounted systems, such as the EM12, is significantly different from that of conventional sidescan sonars, such as GLORIA, and the backscatter images from the two types differ in various respects. Because of the wide variations in incidence angle that are common with hull-mounted systems, and the importance of incidence angle in determining backscatter strength, it is vital to consider the effect of incidence angle during interpretation. 相似文献
256.
If we assume that the periodic brightness variations ina Kuiper Belt lightcurve are determined only by theiraspherical shapes and the observing geomtry, the fractionof detectable Kuiper Belt lightcurves and the lightcurveamplitude distribution can be used to constrain the shapesof Kuiper Belt objects. The results indicate that most KuiperBelt objects (~85%) have shapes that are close to spherical(a/b ≤ 1.5$), but there is a small but significant fraction(~12%) possessing highly aspherical shapes (a/b ≥ 1.7).The distribution cannot be well fitted by a gaussian and is betterapproximated by a power law. 相似文献
257.
Sarah L. WILKISON Timothy J. McCOY Jane E. McCAMANT Mark S. ROBINSON Daniel T. BRITT 《Meteoritics & planetary science》2003,38(10):1533-1546
Abstract— Densities and porosities of meteorites are physical properties that can be used to infer characteristics of asteroid interiors. We report density and porosity measurements of 42 pieces of 30 ordinary chondrites and provide a quantification of the errors of the gas pycnometer method used in this study. Based on our measurements, we find that no significant correlation exists between porosity and petrologic grade, chemical group, sample mass, bulk and grain density, or shock level. To investigate variations in porosity and density between pieces of a meteorite, we examined stones from two showers, Holbrook and Pultusk. Examination of nine samples of Holbrook suggests relative homogeneity in porosity and density between pieces of this shower. Measurements of three samples of Pultusk show homogeneity in bulk density, in contrast to Wilkison and Robinson (2000), a study that reported significant variations in bulk density between 11 samples of Pultusk. Finally, examination of two friable ordinary chondrites, Bjurböle and Allegan, reveal variability in friability and porosity among pieces of the same fall. We suggest that friable ordinary chondrites may have formed in a regolith or fault zone of an asteroid. 相似文献
258.
259.
Firm finances, weather derivatives and geography 总被引:1,自引:0,他引:1
This paper considers some intellectual, practical and political dimensions of collaboration between human and physical geographers exploring how firms are using relatively new financial products - weather derivatives - to displace any costs of weather-related uncertainty and risk. The paper defines weather derivatives and indicates how they differ from weather insurance products before considering the geo-political, cultural and economic context for their creation. The paper concludes by reflecting on the challenges of research collaboration across the human-physical geography divide and suggests that while such initiatives may be undermined by a range of institutional and intellectual factors, conversations between physical and human geographers remain and are likely to become increasingly pertinent. The creation of a market in weather derivatives raises a host of urgent political and regulatory questions and the confluence of natural and social knowledges, co-existing within and through the geography academy, provides a constructive and creative basis from which to engage with this new market and wider discourses of uneven economic development and climate change. 相似文献
260.
On August 31th, 2006 the California Senate shelved SB1056, a bill which would have granted the State jurisdiction over the regulation of seed and nursery stock. Ostensibly proposed to ensure “a level playing field” for agricultural and food producers, SB1056 is one of a host of legislation drafted across the United States to preempt county and municipal bans on genetically engineered crops. In California, the heated struggle around “preemption” exemplifies the interweaving of neoliberal ideology with industry attempts to prevent an unfavorable regulatory environment, but more importantly the contingencies and vulnerabilities of this strategy. After reviewing SB1056’s history, this paper examines how a diverse opposition movement capitalized on the friction between the neoliberal arguments mobilized by supporters and dominant Californian political philosophies. The paper then highlights the ultimate effect of SB1056 through a critical exploration of current state and federal regulation and the entrenched interests of the California government. I argue that more than simply opening new spaces for accumulation, SB1056 would have muted opposition voices and transferred power to institutions financially committed to the technology’s commercialization. 相似文献