全文获取类型
收费全文 | 190篇 |
免费 | 13篇 |
国内免费 | 21篇 |
专业分类
大气科学 | 3篇 |
地球物理 | 23篇 |
地质学 | 87篇 |
海洋学 | 24篇 |
天文学 | 67篇 |
综合类 | 7篇 |
自然地理 | 13篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 17篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 8篇 |
2012年 | 17篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 10篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1993年 | 2篇 |
1989年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有224条查询结果,搜索用时 31 毫秒
131.
即墨温泉地热水的氢氧同位素特征及其地质意义 总被引:2,自引:0,他引:2
青岛市即墨温泉水是含有多种微量元素的一种具特殊医疗作用的地热水。通过对即墨温泉地区在不同季节采集的温泉地热水、地下水、地表水、大气降水和近岸海水分别进行氢、氧同位素的测定。结果表明,即墨温泉水的氢、氧同位素值皆小于大气降水来源的地表水、地下水和雨水;即墨温泉地热水占δD-δ^18O相关点沿大气降水线展布表明其主要来源和补给源为大气降水,估算的循环深度约为2017.6m。在有利的构造部位和良好的储水条件下,大气降水经深循环加热和水岩反应淋滤盐分,并沿断裂上升出露地表,形成矿化度较高的温泉。 相似文献
132.
133.
河流颗粒有机质提供了陆地碳循环的重要信息以及人类活动的记录,通过河口地区沉积物有机质组成,可反映流域变化及海陆间相互作用。2010-2011年分两次于鸭绿江河口西岸潮滩采集柱样4根及表层样23个。对样品进行有机质碳氮总量(TOC、TN)、碳氮同位素(δ13C、δ15 N)及沉积物粒度测试。分析结果表明,由河口向西,有机质受改造程度加深且来源逐渐复杂化,致TOC/TN与δ13C的相关性逐渐降低,δ15 N与沉积物粒度的相关性也随之降低。文中以δ13C为主线探讨沉积物有机质的来源及运移,TOC/TN作为辅助,δ15 N则用于指示生化条件的改变。柱样的δ13 C分布与河流入海输沙密切相关,水库对入海泥沙的拦截,致河口潮滩沉积速率减缓,从而增加了沉积物中海源有机质的含量,δ13C随之增加。潮滩西侧柱样的δ15 N增加指示了生活工业污水的大量排放。此外,表层样δ13C分布的方向性,指示了西水道门口处的快速堆积及潮下带物质的向岸运移,并在西岸潮滩向岸一侧富集。 相似文献
134.
δ13C和δ15N指示不同生态类型湖泊无机氮及有机质来源 总被引:2,自引:0,他引:2
为了探讨不同生态类型湖泊(天然湖泊、城市湖泊)中无机氮和有机质来源,分别采集湖泊中水体、表层沉积物、水生植物、底栖动物进行碳、氮同位素特征分析.结果表明:蚌湖水体δ15N-NH4均值为-1.8‰±1.0‰,δ15N-NO3-均值为-0.5‰±1.7‰,说明蚌湖水体氮表现为雨水和农业肥料氮污染;象湖δ15 N-NH4+均值为6.8‰±8.6‰,其中养殖废水和管道排污口δ15N-NH4+值分别为13.5‰和25.4‰,表现出污水氮同位素特征,象湖δ15 N-NO3-均值为-2.9‰±4.2‰,是氨的硝化作用引起的氮同位素分馏所致.蚌湖表层沉积物、水生植物δ15N差别不大,分别为6.6‰±0.3‰、7.1‰±0.7‰,水生植物δ13C均值为-27.5‰±0.3‰,比沉积物δ13C偏负3‰.有机C/N为9.4±0.5,比沉积物C/N明显偏高6,反映水生植物是蚌湖有机质的主要来源.象湖表层沉积物δ15N、δ13C及有机C/N分布范围大,δ15N在3.6‰~8.3‰之间,均值为5.9‰±1.6‰,δ13C在-27.1‰~-24.7‰之间,均值为-26.0‰±1.0‰,有机C/N在2.6 ~10.8之间,均值为6.2±2.7,表明城市湖泊沉积有机质来源复杂.2个湖泊蚌类δ15N组成与各自湖泊表层沉积物δ15N组成相对应. 相似文献
135.
Seasonal signals of stable isotopes in precipitation, combined with measurements of isotope ratios in soil water, can be used for quantitative estimation of groundwater recharge rates. This study investigates the applicability of using the piston flow principle and the peak shift displacement method to estimate actual groundwater recharge rates in a humid Nordic region located in the province of Quebec, Canada. Two different sites with and without vegetation (C1 and C2) in an unconfined aquifer were tested by measuring soil water isotope ratios (18O/16O and 2H/1H) and volumetric pore water content. Core samples were obtained along the vadose zone down to the groundwater table at the two sites (2.45 m for Site C1 and 4.15 m for Site C2). The peak shift method to estimate groundwater recharge rates was shown to be accurate only in certain specific conditions inherent to the soil properties and the topographical situation of the investigated sites. Indeed, at Site C2, recharge from the snowmelt could not be estimated because of heterogeneity in the lower part of the vadose zone. At this same site the later recharge after the snowmelt (in the period from late spring to early autumn) could be estimated accurately because the upper part of the vadose zone was homogeneous. Furthermore, at site C1, runoff/runon phenomena hampered calculations of actual infiltration and thus produced inaccurate results for recharge. These two different site effects (heterogeneity in the first site and runoff/runon in the other site) were identified as being limiting factors in the accurate assessment of actual recharge. This study therefore recommends the use of the peak shift method for (1) humid Nordic regions, (2) homogeneous and thick vadose zones, and (3) areas with few or limited site effects (runoff/runon). 相似文献
136.
沉积物插管短柱样品于2013年4月采自大连湾2010年“7·16”溢油事故污染区,BQ050站与BQ007站分别位于生物分散剂和化学分散剂喷洒区。沉积物的可溶有机质含量(沥青A)、有机碳同位素组成(δ13Corg)和210Pb比活度分析结果表明:喷洒生物分散剂的重污染区(BQ050站),沉积物中TOC含量为0.58%~1.51%,平均为1.15%;δ13Corg值为-22.2‰~-20.5‰PDB,平均为-21.74‰PDB;沥青A含量为0.061 5%~0.566 4%,平均为0.174 9%;沥青A/TOC比值为7.0%~34.8%,平均为14.13%;210Pbex比活度存在异常峰值分布,垂向分布特征与沥青A相似;2~16 cm段沉积物的可溶有机质具有明显的外来输入特征。喷洒化学分散剂的较轻污染区(BQ007站),沉积物中TOC含量为0.61%~1.14%,平均为0.87%,除8~14 cm层段外,比BQ050站略低;但沥青A含量与沥青A/TOC比值明显低于前者;δ13Corg值较BQ050站轻;210Pbex比活度随柱样深度呈指数衰减,对数相关;外来有机质输入量较低。截至2013年4月,BQ050站溢油污染物在海底下16 cm深度处有特征信号,溢油污染物沥青A 组分垂向迁移距离约为15 cm。 相似文献
137.
Chris Koen Ruby Van Rooyen Francois Van Wyk Freddy Marang 《Monthly notices of the Royal Astronomical Society》1999,309(4):1051-1062
HD 23194, a member of the Pleiades, was found to pulsate with a period of about 30 min. The literature on the star is reviewed, and it is concluded that it may be a marginal Am star in a binary system. HD 95321 is an evolved Am ( ρ Puppis) star with a 5.1-h periodicity. Mode identification of its pulsation, based on multicolour photometry, suggests that the oscillation is probably non-radial with ℓ=2. We also report on the discovery of six other new δ Scuti stars, some of which may be pulsating in gravity modes. 相似文献
138.
Macroalgae contribute to intertidal food webs primarily as detritus, with unclear implications for food web studies using stable isotope analysis. We examined differences in the thallus parts of two South African rhodophytes (Gelidium pristoides and Hypnea spicifera) and changes in overall δ13C, δ15N signatures and C:N ratios during degradation in both the field and laboratory. We hypothesized that both degrading macroalgal tissue and macroalgal-derived suspended particulate material (SPM) would show negligible changes in δ13C, but enriched δ15N signatures and lower C:N ratios relative to healthy plants. Only C:N laboratory ratios conformed to predictions, with both species of macroalgae showing decomposition related changes in δ13C and significant depletions in δ15N in both the field and laboratory. In the laboratory, algal tissue and SPM from each species behaved similarly (though some effects were non-significant) but with differing strengths. Gelidium pristoides δ13C increased and C:N ratios decreased over time in tissue and SPM; δ15N became depleted only in SPM. Hypnea spicifera, δ13C, δ15N and C:N ratios all decreased during degradation in both SPM and algae. 相似文献
139.
S. Pasquaud P. Elie C. Jeantet I. Billy P. Martinez M. Girardin 《Estuarine, Coastal and Shelf Science》2008
Carbon and Nitrogen stable isotopes and stomach contents analyses were used to investigate an estuarine fish food web and identify the contribution of these two methods to the knowledge and understanding of the food web's structure and its functioning. The nine most abundant fish species during the warm period in the Gironde estuary (southwest France, Europe) are examined. Observation of the stomach contents reflects a variety of feeding modes between fish species that consume a diverse assortment of prey, with limited dietary overlap. Nevertheless, when regarding the whole fish community, few prey species dominate the stomach contents. Nitrogen isotope ratios indicate a high intraspecific variability inducing an interspecific covering of the signatures. However, a tendency to δ15N enrichment according to the trophic position of the species studied was observed. Fish assemblages show a trend towards enrichment of their carbon isotopic signatures from the upper estuary (−20.8 ± 1.8‰) towards the lower estuary (−18.3 ± 1.6‰). But whatever the capture zone considered, most of the individual δ13C values for each fish analysed are comprised between −22 and −16‰. Only few specimens, belonging to migratory amphihaline species, have significantly lighter values. 相似文献
140.