全文获取类型
收费全文 | 453篇 |
免费 | 49篇 |
国内免费 | 94篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 4篇 |
地球物理 | 115篇 |
地质学 | 89篇 |
海洋学 | 296篇 |
天文学 | 2篇 |
综合类 | 53篇 |
自然地理 | 33篇 |
出版年
2024年 | 6篇 |
2023年 | 11篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 6篇 |
2016年 | 17篇 |
2015年 | 23篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 24篇 |
2011年 | 21篇 |
2010年 | 13篇 |
2009年 | 27篇 |
2008年 | 24篇 |
2007年 | 38篇 |
2006年 | 24篇 |
2005年 | 27篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 2篇 |
排序方式: 共有596条查询结果,搜索用时 15 毫秒
571.
We report the results from a 250 km long transect, from the Danish coast to the North Sea at 55°30′ N, which was sampled every
32 km in order to study the composition and distribution of phytoplankton, and their dependence on the distance from the coast,
depth and other environmental factors. Altogether 144 species of algae were identified by light, epifluorescence and electron
microscopy. Some ecological preferences were found on the basis of measured environmental parameters and compared with the
literature. Possible controlling mechanisms for the distribution patterns of the plankton algae were analyzed by multivariate
statistics. Only distance from the coast was found to be a significant factor for algal distribution along the transect. Three
main areas of the transect were found: the coastal, middle and oceanic areas. Diatoms, mainly the centric ones, were the most
abundant group of algae. The other less abundant groups were Dinophyceae, Dictyochophyceae, Prasinophyceae and Chlorophyceae.
The pattern of distribution of diatoms and dinophytes along the transect was more or less similar, with larger numbers of
cells found close to both the eastern and western parts of the transect, although the species composition was different. Some
species were found to prefer coastal waters, other species were characterized as oceanic, and several species were found at
all stations. Porosira glacialis showed an atypical distribution along the transect, with highest abundances at both coastal and oceanic stations. 相似文献
572.
The seasonal occurrence of 94 benthic algal species, including Cyanophyta, was observed on a monthly basis over one year in the Patos Lagoon estuary (32°S, 52°W), Brazil, and showed three patterns of algal periodicity. An aseasonal group of 46 species was present throughout the year and two groups of 24 species each occurred either during summer and fall or winter and spring. The seasonal growth of 55 green, brown and red algae was correlated with monthly variations of salinity, water temperature, daylength and light radiation energy, which were measured daily in the estuary. Summer/fall peak growth was observed in 15 algae most of which correlated significantly with high salinities alone or in combination with other factors during this period. Growth peak of 11 species in winter/spring was principally a function of low water temperatures alone or together with a reduced light regime.Both periodicity of benthic algae and their seasonal growth, as a more sensitive measure of their floristic affinity, demonstrated the presence of cool temperate and tropical elements in this flora typical for warm temperate biogeographic regions. Correlations between seasonal variation of algal growth and selected environmental parameters aided in the evaluation of causal factors for algal seasonality. 相似文献
573.
两种大型海藻粉对重金属离子吸附热力学的研究 总被引:4,自引:0,他引:4
本文探讨了两种常见大型海藻,即马尾藻(Sargassum fusiforme)和海带(Laminaria japonica)对重金属离子(Cu^2 、Pb^2 、Cd^2 、Ni^2 )的吸附热力学过程.结果表明,这两种海藻粉对重金属离子的吸附曲线基本符合Langmuir吸附模型,其吸附容量受温度的影响,马尾藻和海带粉对Cu^2 的吸附均为吸热过程;25℃和35℃两组实验结果显示,其吸附容量随温度的升高而增加,吸附热分别为59.9、76.8kJ/mol. 相似文献
574.
福建红树林区4种海藻的营养成分 总被引:1,自引:0,他引:1
主要对福建红树林区4种海藻(扁浒苔Enteromorpha compressa,混合卷枝藻Bostrychia mixta,鹧鸪菜Caloglossa leprieurii,节附链藻Catenella impudica)的营养元素和氨基酸含量等进行研究.结果表明:(1)福建红树林区 4种海藻Fe,Mn含量显著高于一般海藻的平均浓度;Ca含量则普遍低于一般海藻的平均浓度;P,K,Mg含量则高于或低于一般海藻的平均浓度;(2)福建红树林区4种海藻总氨基酸含量(TAA)由高到低依次为(干重):扁浒苔265.89mg/g,混合卷枝藻211.96mg/g,鹧鸪菜189.53mg/g,节附链藻111.10mg/g;而必需氨基酸含量(EAA)由高到低依次为:混合卷枝藻87.42mg/g,扁浒苔82.92mg/g,鹧鸪菜73.62mg/g,节附链藻34.41mg/g;(3)在3和6月,对生长在秋茄板状根上和岩石面上的鹧鸪菜营养成分比较,前者的总氨基酸和必需氨基酸含量均大于后者;而元素含量则有不同变化. 相似文献
575.
南极冰藻Chlorophyceae L-4抗氧化酶活性对UV-B辐射增强的响应 总被引:2,自引:0,他引:2
为了了解在UV B辐射增强的胁迫下,南极冰藻ChlorophyceaeL 4细胞内保护酶系统对活性氧自由基的清除作用,对不同辐射强度下ChlorophyceaeL 4细胞中丙二醛含量的变化、自由基的产生速率和相应的保护酶系统的变化进行了测定。结果表明,在UV B辐射增强的初期(1~3d),ChlorophyceaeL 4中丙二醛含量的迅速提高,但随后很快降低,在低强度UV B(35μW·cm-2)辐照下保护酶活性能够恢复到基本水平。在UV B辐射增强的胁迫下,ChlorophyceaeL 4中的超氧化物歧化酶、过氧化物酶和过氧化氢酶的活性明显比对照组的高,而且在高强度(70μW·cm-2)的辐照下,酶活性更高。ChlorophyceaeL 4中的抗坏血酸过氧化物酶的活性在UV B辐射增强的胁迫下略有升高或变化不大。本研究结果表明,保护酶系统在南极冰藻适应南极强辐射环境中起着非常重要的作用。 相似文献
576.
P. Czar 《Geological Journal》2005,40(4):405-424
Calcareous microflora occur commonly in the early Serpukhovian (late Mississippian) rocks from the Guadiato Area (southwestern Spain) despite the fact that this area contains mostly siliciclastic sediments. The microflora recorded in the carbonate beds is regarded as representative of both relatively deep‐water and shallow‐water facies and can be compared with the slope and shelf facies environments distinguished in the Guadiato Area. Up to 45 algal taxa have been identified in the carbonate beds, of which 26 taxa occur in the relatively deep‐water assemblages, whereas the shallow‐water assemblages are composed of up to 43 taxa. The entire algal assemblage is dominated by calcifoliids, common cyanobacteria and incertae sedis, but the shallow‐water assemblages contain more commonly dasyclads, red algae and aoujgaliids. Most of these taxa are present, but poorly known, in other Serpukhovian carbonate platforms in the western Palaeotethys. Some algae (Hortonella uttingii, Kamaenella tenuis and Koninckopora inflata), usually regarded as being restricted to the Viséan, have been found in Serpukhovian rocks in the Guadiato Area, and also in Algeria, thus their stratigraphic ranges might be extended up to the Serpukhovian. Other important taxa include: Archaeolithophyllum, Cabrieropora, Calcifolium, Falsocalcifolium, Fourstonella, Frustulata, Kulikia, Neoprincipia and ‘Windsoporella’, which are exceptionally recorded in Serpukhovian rocks, or not recorded at all, because they are typically recorded in the Pennsylvanian (cf. Clavaporella), although some of them show earlier occurrences in Viséan rocks (Claracrusta, Paraepimastopora and Sparaphralysia). Some of the algal taxa can be considered as potential regional markers for the Serpukhovian, such as Archaeolithophyllum, cf. Clavaporella, Frustulata and Girvanella (?) sp. The algal assemblages found in the Guadiato Area show the greatest similarities with those in the Béchar‐Mézarif (Algeria), Pyrenees and Montagne Noire (southern France). Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
577.
从孢粉、藻类化石组合看长江三角洲第一硬质粘土层的成因及其古环境意义 总被引:23,自引:10,他引:13
文章通过对长江三角洲南翼7个钻孔样品的孢粉、藻类分析,从晚第四纪第一硬质粘土层中提取出了种类和数量均较可观的孢粉、藻类化石,从而可以判别第一硬质粘土层形成时的沉积环境和植被类型,为长江三角洲地区硬质粘土层的成因研究提供了生物化石依据。研究结果表明,第一硬质粘土层中有多种孢粉、藻类化石组合。高含量淡水藻类的存在说明硬质粘土形成受到流水的作用,亦即硬粘土的形成环境可能为水域环境。化石组合中含量较低的海生沟鞭藻表明,长江三角洲地区在硬质粘土形成时曾受到海水影响。硬质粘土层中的禾本科-莎草科-落叶栎-松、禾本科-落叶栎-松-蒿和莎草科-落叶栎-香蒲孢粉组合指示研究区低地为平原区草甸,而周边的山地有针阔叶混交林分布,当时该地区属于温凉略湿的温带气候。 相似文献
578.
四川黄龙钙华藻类及其生物岩溶作用 总被引:3,自引:0,他引:3
从探索黄龙钙华的生物成因角度出发,对黄龙钙华藻类进行了采集、鉴定和分析,并对钙华藻类的生物岩溶作用做了初步探讨。研究得出黄龙钙华藻类分属于4门19属86种,优势种属为Tolypothrix属、Gloeocapsa属和Cymbella属。黄龙景区不同环境区域的优势藻类有所不同,藻类参与的碳酸盐沉积在不同岩溶景观中所起作用也有所差异。其中蓝藻参与的碳酸盐沉积主要表现于黄龙钙华坝景观的形成过程中,由硅藻参与碳酸盐沉积主要表现于斜坡滩华景观的形成过程中。藻类既能在钙华形成过程中发挥作用,藻类的生长也能侵蚀破坏钙华景观,在长期缺乏岩溶水补给的条件下,藻类对钙华景观的破坏性尤为突出。 相似文献
579.
不同氮源对微藻增殖的影响 总被引:12,自引:1,他引:11
采用室内实验的方式研究了无机氮和有机氮对不同微藻增殖的影响情况。比较了不同氮源(氯化铵和尿素)对纤细角毛藻(Chaetoceros gracilis)、赤潮异弯藻(Heterosigma akashiwo Hada)、亚历山大藻(Alexandrium sp.)、隐藻(Chroomonas salina f.adolenscens)4种海洋微藻生长的不同影响。结果表明,有机氮尿素对海洋微藻增殖的影响比无机氮的复杂。由微藻最适生长的氮、磷浓度得到N:P值,讨论了该值对微藻增殖的影响,以及影响N:P值的可能情形。 相似文献
580.
Diel tuning of photosynthetic systems in ice algae at Saroma-ko Lagoon, Hokkaido, Japan 总被引:1,自引:0,他引:1
Shimpei Aikawa Hiroshi Hattori Yasushi Gomi Kentaro Watanabe Sakae Kudoh Yasuhiro Kashino Kazuhiko Satoh 《Polar Science》2009,3(1):57-72
Ice algae are the major primary producers in seasonally ice-covered oceans during the cold season. Diurnal change in solar radiation is inevitable for ice algae, even beneath seasonal sea ice in lower-latitude regions. In this work, we focused on the photosynthetic response of ice algae under diurnally changing irradiance in Saroma-ko Lagoon, Japan. Photosynthetic properties were assessed by pulse-amplitude modulation (PAM) fluorometry. The species composition remained almost the same throughout the investigation. The maximum electron transport rate (rETRmax), which indicates the capacity of photosynthetic electron transport, increased from sunrise until around noon and decreased toward sunset, with no sign of the afternoon depression commonly observed in other photosynthetic organisms. The level of non-photochemical quenching, which indicates photoprotection activity by dissipating excess light energy via thermal processes, changed with diurnal variations in irradiance. The pigment composition appeared constant, except for xanthophyll cycle pigments, which changed irrespective of irradiance. These results indicate that ice algae tune their photosynthetic system harmonically to achieve efficient photosynthesis under diurnally changing irradiance, while avoiding damage to photosystems. This regulation system may be essential for productive photosynthesis in ice algae. 相似文献