全文获取类型
收费全文 | 149篇 |
免费 | 6篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 11篇 |
地球物理 | 48篇 |
地质学 | 53篇 |
海洋学 | 17篇 |
天文学 | 15篇 |
综合类 | 1篇 |
自然地理 | 9篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 8篇 |
2012年 | 4篇 |
2011年 | 5篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 6篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有156条查询结果,搜索用时 31 毫秒
1.
Iron solubility equilibria were investigated in seawater at 36.22‰ salinity and 25°C using several filtration and dialysis techniques. In simple filtration experiments with 0.05 μm filters and Millipore ultra-filters, ferric chlorides fluorides, sulfates, and FeOH2+ species were found to be insignificant relative to Fe(OH)2+ at p[H+] = ?log [H+] greater than 6.0. Hydrous ferric oxide freshly precipitated from seawater yielded a solubility product of . Solubility studies based on the rates of dialysis of various seawater solutions and on the filtration of acidified seawater solutions indicated the existence of the Fe(OH)30 species. The formation constant for this species can be calculated as . The Fe(OH)4? species is present at concentrations which are negligible compared to Fe(OH)2+ and Fe(OH)30 in the normal pH range of seawater. However, there is at least one other significant ferric complex in seawater above p[H+] = 8.0 (possibly with bicarbonate, carbonate, or borate ions) in addition to the Fe(OH)2+ and Fe(OH)30 species. 相似文献
2.
Partial equivalent conductances and partial equivalent volumes of the major constituents in seawater were used to evaluate the specific gravity-conductivity-chlorinity-salinity relationships in the marine environment. For example, in the open ocean, the relationships between Cl‰ and both S‰ and specific gravity are valid to within 0.014‰ and 0.014 σt, respectively. The relationships between conductivity and S‰ and specific gravity are valid to within 0.006‰ and 0.007 σt. In river diluted nearshore areas specific gravity anomalies inferred from Cl‰, can be as great as 0.06 σt and 0.04 σt when inferred from a conductivity ratio measurement. 相似文献
3.
Copper in a series of samples from the northwestern Atlantic has been determined by anodic stripping voltammetry (ASV) and atomic absorption spectrometry after preconcentration by cobalt—APDC coprecipitation. Samples from a transect across the continental shelf directly off the New York Bight showed a linear relationship between total copper and salinity (31–34‰) and less than 5% of the total copper was detectable by ASV. A slope water station showed less than 9% of the total copper to be ASV detectable in the upper 780m, below which the ASV detectable copper increased to 70% at 3000 m. The Sargasso Sea profiles showed less than 7% ASV detectable copper in the upper 150 m; the fraction of the total copper detected by ASV increased to about 80% of the total copper at greater depths. The reduced availability of copper to the ASV measurement in coastal waters and open ocean surface waters appears to be related to recent contact with waters where biological productivity occurs. 相似文献
4.
Arthur C. R. Gleason Diego Lirman Dana Williams Nuno R. Gracias Brooke E. Gintert Hossein Madjidi R. Pamela Reid G. Chris Boynton Shahriar Negahdaripour Margaret Miller & Philip Kramer 《Marine Ecology》2007,28(2):254-258
Four hurricanes impacted the reefs of Florida in 2005. In this study, we evaluate the combined impacts of hurricanes Dennis, Katrina, Rita, and Wilma on a population of Acropora palmata using a newly developed video‐mosaic methodology that provides a high‐resolution, spatially accurate landscape view of the reef benthos. Storm damage to A. palmata was surprisingly limited; only 2 out of 19 colonies were removed from the study plot at Molasses Reef. The net tissue losses for those colonies that remained were only 10% and mean diameter of colonies decreased slightly from 88.4 to 79.6 cm. In contrast, the damage to the reef framework was more severe, and a large section (6 m in diameter) was dislodged, overturned, and transported to the bottom of the reef spur. The data presented here show that two‐dimensional video‐mosaic technology is well‐suited to assess the impacts of physical disturbance on coral reefs and can be used to complement existing survey methodologies. 相似文献
5.
Coastal Habitat Use and Residency of Juvenile Atlantic Sharpnose Sharks (Rhizoprionodon terraenovae)
John K. Carlson Michelle R. Heupel Dana M. Bethea Lisa D. Hollensead 《Estuaries and Coasts》2008,31(5):931-940
Coastal habitat use and residency of a coastal bay by juvenile Atlantic sharpnose sharks, Rhizoprionodon terraenovae, were examined by acoustic monitoring, gillnet sampling, and conventional tag–recapture. Acoustic monitoring data were used to define the residency and movement patterns of sharks within Crooked Island Sound, Florida. Over 3 years, sharks were monitored for periods of 1–37 days, with individuals regularly moving in and out of the study site. Individual sharks were continuously present within the study site for periods of 1–35 days. Patterns of movement could not be correlated with time of day. Home range sizes were typically small (average?=?1.29 km2) and did not vary on a yearly basis. Gillnet sampling revealed that juvenile Atlantic sharpnose sharks were present in all habitat types found within Crooked Island Sound, and peaks in abundance varied depending on month within a year. Although telemetry data showed that most individuals remained within the study site for short periods of time before emigrating, conventional tag–recapture data indicates some individuals return to Crooked Island Sound after extended absences (maximum length?=?1,352 days). Although conventional shark nursery theory suggests small sharks remain in shallow coastal waters to avoid predation, juvenile Atlantic sharpnose sharks frequently exited from protected areas and appear to move through deeper waters to adjacent coastal bays and estuaries. Given the high productivity exhibited by this species, the benefit gained through a nursery that reduces predation may be limited for this species. 相似文献
6.
Mid-infrared imaging photometry of the Orion BN/KL infrared cluster at eight wavelengths between 5 and 20µm using a 58 × 62 pixel imaging array camera has revealed new compact sources and the large-scale structure of the region in diffraction-limited (1 arcsec) detail. Several new objects have been detected within a few arcsec of IRc2, widely thought to be the principal luminosity source for the entire BN/KL complex. Detailed color temperature and emission opacity images are derived from the 7.8, 12.4 and 20.0µm observations, and the 9.8µm image is used to derive an image of silicate dust extinction for the region. The color temperature, opacity, and extinction images show that IRc2 may not be the single dominant luminosity source for the BN/KL region; substantial contributions to the luminosity could be made by IRc7, BN, KL, and five new compact 10µm sources detected within a few arcseconds of IRc2. We suggest that a luminous, early-type star near IRc2, which is associated with the compact radio source I and the Orion SiO maser, is the dominant luminosity source in the BN/KL region, hidden from view by cool dust material with at least Av 60 mag of visible extinction. 相似文献
7.
武汉市区第四系含水层地下水有机污染敏感性研究 总被引:14,自引:0,他引:14
在详细调查武汉市水文地质条件和地下水污染现状的基础上,获得了高精度的武汉市水环境中微量有机污染物的组成数据。所检测出的有机组分达30余种,以苯及相关苯系物为主,污染程度较高的地下水主要分布在人口密集区和工业,商业区,应用改进的DRASTIC模型-地下水污染敏感性评价模型,在GIS平台上,编制了武汉市区地下水污染敏感性分区图。根据其评价结果,建议集中对那些敏感性相对较高的区域采取有效的环保措施,开发利用时应作出风险评价。 相似文献
8.
Dana Micu 《Meteorology and Atmospheric Physics》2009,105(1-2):1-16
Snow pack characteristics and duration are considered to be key indicators of climate change in mountain regions, especially during the winter season (herein considered to last from the 1st of November to the 30th of April). Deviations recorded in the regime of the main explanatory variables of snow pack changes (i.e. temperature and precipitation) offer useful information on winter climate variability, in the conditions of the winter warming trend already seen in some areas of the Romanian Carpathians. The present work focuses on changes and trends in snow pack characteristics and its related parameters, registered at the 15 weather stations located in the alpine, sub-alpine and forest belts in all the three Romanian Carpathian branches (>1,000 m) over the 1961–2003 period. Changes in the snow pack regime were investigated in relation with the modifications of winter temperature and precipitation having been detected mostly at the end of the twentieth century. A winter standardized index was calculated to group winters over the 43-year period into severity classes and detect the respective changes. Links between the number of snow cover days and seasonal NAO index were also statistically analysed in this study. The general results show large regional and altitudinal variations and the complex character of the climate in the Romanian Carpathians, leading to the idea of an ongoing warming process associated with a lower incidence of snow cover, affecting to a large extent the forested mountain areas located below 1,600–1,700 m altitude. Also negative and weak correlations were found, particularly over the December–March interval, between the number of snow cover days and seasonal NAO index values. 相似文献
9.
Hannah M. Clilverd Yin‐Phan Tsang Dana M. Infante Abigail J. Lynch Ayron M. Strauch 《水文研究》2019,33(5):699-719
Climate change has fundamentally altered the water cycle in tropical islands, which is a critical driver of freshwater ecosystems. To examine how changes in streamflow regime have impacted habitat quality for native migratory aquatic species, we present a 50‐year (1967–2016) analysis of hydrologic records in 23 unregulated streams across the five largest Hawaiian Islands. For each stream, flow was separated into direct run‐off and baseflow and high‐ and low‐flow statistics (i.e., Q10 and Q90) with ecologically important hydrologic indices (e.g., frequency of flooding and low flow duration) derived. Using Mann–Kendall tests with a running trend analysis, we determined the persistence of streamflow trends through time. We analysed native stream fauna from ~400 sites, sampled from 1992 to 2007, to assess species richness among islands and streams. Declines in streamflow metrics indicated a general drying across the islands. In particular, significant declines in low flow conditions (baseflows), were experienced in 57% of streams, compared with a significant decline in storm flow conditions for 22% of streams. The running trend analysis indicated that many of the significant downward trends were not persistent through time but were only significant if recent decades (1987–2016) were included, with an average decline in baseflow and run‐off of 10.90% and 8.28% per decade, respectively. Streams that supported higher native species diversity were associated with moderate discharge and baseflow index, short duration of low flows, and negligible downward trends in flow. A significant decline in dry season flows (May–October) has led to an increase in the number of no‐flow days in drier areas, indicating that more streams may become intermittent, which has important implications for mauka to makai (mountain to ocean) hydrological connectivity and management of Hawai'i's native migratory freshwater fauna. 相似文献
10.
Dana?L.?DrewEmail author Ilya?N.?Bindeman Matthew?W.?Loewen Paul?J.?Wallace 《Contributions to Mineralogy and Petrology》2016,171(1):10
During the onset of caldera cluster volcanism at a new location in the Snake River Plain (SRP), there is an increase in basalt fluxing into the crust and diverse silicic volcanic products are generated. The SRP contains abundant and compositionally diverse hot, dry, and often low-δ18O silicic volcanic rocks produced through time during the formation of individual caldera clusters, but more H2O-rich eruptive products are rare. We report analyses of quartz-hosted melt inclusions from pumice clasts from the upper and lower Arbon Valley Tuff (AVT) to gain insight into the initiation of caldera cluster volcanism. The AVT, a voluminous, caldera-forming rhyolite, represents the commencement of volcanism (10.44 Ma) at the Picabo volcanic field of the Yellowstone hotspot track. This is a normal δ18O rhyolite consisting of early and late erupted members (lower and upper AVT, respectively) with extremely radiogenic Sr isotopes and unradiogenic Nd isotopes, requiring that ~50 % of the mass of these elements is derived from melts of Archean upper crust. Our data reveal distinctive features of the early erupted lower AVT melt including: variable F concentrations up to 1.4 wt%, homogenous and low Cl concentrations (~0.08 wt%), H2O contents ranging from 2.3 to 6.4 wt%, CO2 contents ranging from 79 to 410 ppm, and enrichment of incompatible elements compared to the late erupted AVT, subsequent Picabo rhyolites, SRP rhyolites, and melt inclusions from other metaluminous rhyolites (e.g., Bishop Tuff, Mesa Falls Tuff). We couple melt inclusion data with Ti measurements and cathodoluminescence (CL) imaging of the host quartz phenocrysts to elucidate the petrogenetic evolution of the AVT rhyolitic magma. We observe complex and multistage CL zoning patterns, the most critical being multiple truncations indicative of several dissolution–reprecipitation episodes with bright CL cores (higher Ti) and occasional bright CL rims (higher Ti). We interpret the high H2O, F, F/Cl, and incompatible trace element concentrations in the context of a model involving melting of Archean crust and mixing of the crustal melt with basaltic differentiates, followed by multiple stages of fractional crystallization, remelting, and melt extraction. This multistage process, which we refer to as distillation, is further supported by the complex CL zoning patterns in quartz. We interpret new Δ18O(Qz-Mt) isotope measurements, demonstrating a 0.4 ‰ or ~180 °C temperature difference, and strong Sr isotopic and chemical differences between the upper and lower AVT to represent two separate eruptions. Similarities between the AVT and the first caldera-forming eruptions of other caldera clusters in the SRP (Yellowstone, Heise and Bruneau Jarbidge) suggest that the more evolved, lower-temperature, more H2O-rich rhyolites of the SRP are important in the initiation of a caldera cluster during the onset of plume impingement. 相似文献