全文获取类型
收费全文 | 802篇 |
免费 | 48篇 |
国内免费 | 224篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 104篇 |
地球物理 | 346篇 |
地质学 | 340篇 |
海洋学 | 131篇 |
天文学 | 35篇 |
综合类 | 39篇 |
自然地理 | 62篇 |
出版年
2023年 | 7篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2016年 | 12篇 |
2015年 | 19篇 |
2014年 | 36篇 |
2013年 | 24篇 |
2012年 | 47篇 |
2011年 | 52篇 |
2010年 | 16篇 |
2009年 | 24篇 |
2008年 | 47篇 |
2007年 | 39篇 |
2006年 | 41篇 |
2005年 | 50篇 |
2004年 | 50篇 |
2003年 | 39篇 |
2002年 | 36篇 |
2001年 | 30篇 |
2000年 | 35篇 |
1999年 | 23篇 |
1998年 | 16篇 |
1997年 | 20篇 |
1996年 | 11篇 |
1995年 | 17篇 |
1994年 | 23篇 |
1993年 | 28篇 |
1992年 | 25篇 |
1991年 | 27篇 |
1990年 | 30篇 |
1989年 | 26篇 |
1988年 | 30篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 27篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1978年 | 4篇 |
1973年 | 3篇 |
1944年 | 2篇 |
1940年 | 4篇 |
1938年 | 2篇 |
1937年 | 3篇 |
1925年 | 2篇 |
排序方式: 共有1074条查询结果,搜索用时 0 毫秒
141.
东地中海地区最近3次强震的余震衰减 总被引:1,自引:0,他引:1
对东地中海地区最近3次强城的余震序列进行了研究。这3次强震分别是:1995年11月22日Mw=7.1地震、1993年8月3日ML=5.8地震和1996年10月9日MW=6.8地震。前两次地震发生在亚喀巴湾,最后一次发生在塞浦路斯西南海岸的近岸。修正的大森公式对所有事件余震活动的衰减都给出了很好的拟合。亚喀巴湾两个序列的p值相对较低(1993年,p=0.90;1995年,p=0.75),这反映了余震 相似文献
142.
Fazle KARIM 《国际泥沙研究》1999,(2)
1INTRODUCTIONThesouthwesternregionoftheUnitedStates,includingSoutheastArizona,ischaracterizedbyasemiaridclimatewithhotsummers,mildwinters,andephemeralstreamsdrainingsparselyvegetatedareas.ChannelmorphologyoftheephemeralstreamsinSoutheastArizonaisinfluencedbybothlateralandverticalchannelchangesoccurringduringmajorfloods.Lateralchannelchangesoccurinthreewaysbankerosion,meandermigration,andchannelavulsion.Verticalchannelchangesinclude,beddegradationoraggradation,andmayoccurseparatelyorinco… 相似文献
143.
Ryashchenko T. G. Akulova V. V. Solokov V. N. Grigorieva I. J. 段汝文 张振中 孙崇绍 《地震工程学报》1999,21(1):110-111
试样为取自中国北方黄土高原标准剖面①中的马兰(Q3)、离石(Q2)、午城(Q1)以及次生的洪积-冲积(Q4)黄土.各方面成功的配合与多手段的综合性研究使我们能对黄土的微结构模型有了概念,能分析结构特征对黄土某些性质的影响,并可用来解释已提出的有关成因的一些看法. 相似文献
144.
K. Hattori I. Takahashi C. Yoshino N. Isezaki H. Iwasaki M. Harada K. Kawabata E. Kopytenko Y. Kopytenko P. Maltsev V. Korepanov O. Molchanov M. Hayakawa Y. Noda T. Nagao S. Uyeda 张素琴 《国际地震动态》2005,(11):33-44
过去对Spitak,Loma Prieta和Guam地震的研究表明,大地震发生之前都会有相应的磁场异常。为了确认这一事实并详细研究超低频(ULF)现象,日本建立了一个超低频磁力仪的监测网络,开展了包括小型台阵在内的网络观测工作。文中同时介绍了在Matsukawa台站观测到的与Iwateken Nairiku Hokubu地震(震级M6.1级,发生在1998年9月3日,震源深度为10km)相关的地磁资料。分析了4.5年的资料,并对获得的结果进行了讨论。在地震前两个星期,水平和垂直分量之间的谱密度比的(极化)变化表现出异常情况。这是在相当长的数据分析中发现的一次独特的变化,它暗示了这种异常变化可能是大地震孕育期间的一个信号。 相似文献
145.
Polycyclic aromatic hydrocarbons (PAHs) and the trophic structure of polychaete assemblages were studied in sediments at 28 stations in Todos os Santos Bay. Total PAH concentrations varied from 8 to 4163 ng g(-1) dry weight. The indexes used for the determination of PAH origin suggested both pyrolytic and petrogenic sources. A total of 397 individuals of polychaetes was recorded which were classified in three trophic groups. The PCA ordination resulted in the formation of three groups of stations, Group I characterised by sandy sediments, low organic content, low total PAH concentration and percentage of potentially harmful PAH was dominated by subsurface deposit-feeders. The other two groups (IIa and IIb), showed similar percentages of silt and clay, however, Group IIb formed by those stations with high total organic carbon, total nitrogen, sulphur contents, high total PAH concentration and percentage of potentially harmful PAH was dominated by carnivores. Trophic changes could be explained by the level of exposure to PAH effects relative to differences in the life style and feeding strategies between deposit-feeders and carnivores. 相似文献
146.
Parameters of environmental health, including paracellular permeability of external epithelia, functional state of lysosomes and the level of metallothioneins (MTs), were examined using fluorescent markers and vital microfluorometry in different tissues of the marine gastropod, Hexaplex trunculus, from a coal-polluted and coal-free site. Vital microfluorometrical examinations exhibited enhanced paracellular permeability of external epithelia to the anionic marker, fluorescein (FLU), lower lysosomal accumulation of neutral red (NR) as well as higher levels of MTs, when compared with epithelia of gastropods from the coal-free site. Those differences were particularly marked in the foot epithelium, which is in direct contact with the substrate. In addition, cadmium was measured by ICP-AES in the hepatopancreas of gastropods sampled from the coal-polluted site and two coal-free sites. Significantly higher levels of Cd were found in gastropod hepatopancreas from the coal-polluted site. In addition, two months feeding experiments conducted in aquaria containing: (a) coal pieces covered by barnacles; (b) natural rocks covered by barnacles; and (c) natural rocks with barnacles + bare coal pieces, demonstrated significant increase of Cd concentration in the hepatopancreas of the gastropods exposed to coal. We suggest that coal in the marine environment has detrimental effects on marine gastropods, both directly through contact with the organisms and indirectly through the food web. 相似文献
147.
Schmidt H Bich Ha N Pfannkuche J Amann H Kronfeldt HD Kowalewska G 《Marine pollution bulletin》2004,49(3):229-234
The laboratory characterization of a field-operable surface-enhanced Raman scattering sensor (SERS optode) is presented for the detection of aromatic hydrocarbons in seawater. The sensor has been developed for deployment with a robust underwater spectrograph. To meet the demands of the harsh seawater application, sol-gel derived SERS substrates were used. The calibration curves of six PAHs were determined to be of Langmuir adsorption isotherm type with limits of detection ranging from the microg l(-1) to ng l(-1) level. The experimentally determined adsorption constants varied strongly with the molecular weight of the analytes and correlated with their solubility. A mixture of five PAHs dissolved in seawater was investigated to demonstrate the utility of this method for screening. Emphasis was put on the interference from suspended particulate matter (SPM). The Raman measurement with backscattering configuration was shown to be immune against turbidities up to 1000 NTU. The physico-chemical interference arising from adsorption by the sediment was measured on-line by adding sediment to a PAH-spiked solution. According to the calibration curve, the PAH concentration decrease corresponded to more than 98% of the analyte being scavenged by the sediment. 相似文献
148.
Pigments determined by high performance liquid chromatography (HPLC) provide useful information concerning water column and epibenthic plant and microbial communities in both extant communities and accumulated sediments in lakes, estuaries and the ocean. Chlorophyll and its degradation products provide an estimate of overall biomass, and carotenoid pigments provide taxonomic biomarkers of phytoplankton. We examined the pigments preserved in sediment cores from the Louisiana continental shelf adjacent to the outflow of the Mississippi River system to document changes in phytoplankton community composition, phytoplankton abundance, and conditions of hypoxia over time. Carbon accumulated in sediments from water depths of 20-60 m is primarily derived from marine phytoplankton and represents the history of phytoplankton communities in the overlying water. There is a general increase in chlorophyll a, pheopigments, zeaxanthin, fucoxanthin and most carotenoids over time, with the change gradual from 1955 to 1970, followed by a fairly steady increase to 1997. The highest chloropigment concentrations are in cores from areas more likely to be exposed to seasonal hypoxia. These indicate an increase in eutrophication in the form of greater diatom and cyanobacterial production, or a worsening of hypoxia, or both. This trend expanded westward along the Louisiana shelf in the 1990s. 相似文献
149.
Hardman-Mountford NJ Allen JI Frost MT Hawkins SJ Kendall MA Mieszkowska N Richardson KA Somerfield PJ 《Marine pollution bulletin》2005,50(12):1463-1471
Adaptive management of the marine environment requires an understanding of the complex interactions within it. Establishing levels of natural variability within and between marine ecosystems is a necessary prerequisite to this process and requires a monitoring programme which takes account of the issues of time, space and scale. In this paper, we argue that an ecosystem approach to managing the marine environment should take direct account of climate change indicators at a regional level if it is to cope with the unprecedented change expected as a result of human impacts on the earth climate system. We discuss the purpose of environmental monitoring and the importance of maintaining long-term time series. Recommendations are made on the use of these data in conjunction with modern extrapolation and integration tools (e.g. ecosystem models, remote sensing) to provide a diagnostic approach to the management of marine ecosystems, based on adaptive indicators and dynamic baselines. 相似文献
150.
Polybrominated diphenyl ethers (PBDEs) and organochlorines in small cetaceans from Hong Kong waters: levels, profiles and distribution 总被引:9,自引:0,他引:9
Polybrominated diphenyl ethers (PBDEs) and organochlorine compounds (OCs) were determined in the blubber, liver and kidney of Indo-Pacific humpback dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides) stranded in Hong Kong coastal waters during 1995–2001. Among the organohalogen compounds analyzed, DDTs were the most dominant contaminants with concentrations ranging from 9.9 to 470 μg/g lipid wt. PBDEs in Hong Kong cetaceans, which are reported for the first time, were detected in all the samples with values ranging from 0.23 to 6.0 μg/g lipid wt., with a predominance of BDE-47. Results from this study suggest PBDEs should be classified as priority pollutants in Asia. Higher concentrations were found in humpback dolphins than in finless porpoises, and this was attributed mainly to differences in habitat. Elevated residues of PCBs and DDTs in some cetaceans suggest these species may be at risk. 相似文献