全文获取类型
收费全文 | 2956篇 |
免费 | 567篇 |
国内免费 | 829篇 |
专业分类
测绘学 | 364篇 |
大气科学 | 651篇 |
地球物理 | 687篇 |
地质学 | 1485篇 |
海洋学 | 325篇 |
天文学 | 118篇 |
综合类 | 333篇 |
自然地理 | 389篇 |
出版年
2024年 | 13篇 |
2023年 | 35篇 |
2022年 | 138篇 |
2021年 | 190篇 |
2020年 | 138篇 |
2019年 | 144篇 |
2018年 | 159篇 |
2017年 | 162篇 |
2016年 | 171篇 |
2015年 | 142篇 |
2014年 | 191篇 |
2013年 | 196篇 |
2012年 | 217篇 |
2011年 | 198篇 |
2010年 | 189篇 |
2009年 | 179篇 |
2008年 | 155篇 |
2007年 | 174篇 |
2006年 | 122篇 |
2005年 | 137篇 |
2004年 | 106篇 |
2003年 | 78篇 |
2002年 | 95篇 |
2001年 | 95篇 |
2000年 | 104篇 |
1999年 | 101篇 |
1998年 | 125篇 |
1997年 | 108篇 |
1996年 | 80篇 |
1995年 | 69篇 |
1994年 | 74篇 |
1993年 | 55篇 |
1992年 | 46篇 |
1991年 | 40篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1958年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4352条查询结果,搜索用时 343 毫秒
391.
Extreme Earthquake and Earthquake Perceptibility Study in Greece and its Surrounding Area 总被引:3,自引:0,他引:3
The sample interval for the selection of extreme magnitudes plays an important part in the quality of Gumbel model fitting. A short sample interval can produce many observations, which is helpful in obtaining a reliably fitting model. However a short sample interval can bring many dummy ``observations', a condition which adversely biases the fitting. The short sample interval also increases the chance to introduce non-independent observations as well, which violates a basic requirement of the Gumbel model. On the other hand, a large time interval not only reduces the number of observations, but also enlarges the observation error. Thus, for Greece, the most suitable parameters of the third Gumbel extreme model are obtained by using a sample interval which produces minimum error. In consideration of the reliability of the seismic data, earthquakes with magnitude M 5.5 in Greece and its surrounding region after 1900 are used mainly in the present paper. In order to obtain well resolved contour maps with smooth changes a 2°× 2° cell with half-degree overlap strategy was used to scan the region. The most expected largest earthquake for the next fifty, one hundred and two hundred years are estimated for each cell. Likewise, the events with magnitude at a probability of 90\% of non-exceedance over the next fifty, one hundred and two hundred years are estimated for each cell. In parallel to this procedure we also analyze the 67 shallow seismic zones outlined by Papazachos and his colleagues and detail individual zone results where these are obtained. The most perceptible earthquake magnitude for the range of intensities I = {VI}, VII and VIII are also calculated. All results show that the areas around the Hellenic Arc and the Cephalonia Transform Fault for Greece have comparatively high frequency of destructive earthquakes accompanied by a high occurrence probability of moderate earthquakes (M 5.5). 相似文献
392.
本文在系统分析苏锡常地区地下水开采与地面沉降发展动态及相互关系的基础上,从“区域分解”的思想出发,将研究区按第四纪土层结构进行了合理分区,并分别在各亚区建立地面沉降量与地下水水位相关预测模型。实践表明,该模型符合现阶段苏锡常地区地面沉降研究现状,具有一定的实用价值。 相似文献
393.
Types,geological features and geodynamic significances of gold-copper deposits in the Kanggurtag metallogenic belt,eastern Tianshan,NW China 总被引:5,自引:0,他引:5
Lian-Chang?ZhangEmail author Wen-Jiao?Xiao Ke-Zhang?Qin Jin-sheng?Ji Xing-ke?Yang 《International Journal of Earth Sciences》2004,93(2):224-240
Occupying the middle of the central Asia Paleozoic accretionary and collisional orogenic belt, the eastern Tianshan area has a great economic potential due to Au-Cu mineralization during syn- and post- orogenic events. In the Kanggurtag Au-Cu metallogenic belt, three major types of gold deposits have been recognized: ductile-shear-zone-hosted gold deposits, magmatic hydrothermal gold deposits, and epithermal gold deposits. Four kinds of copper deposits have also been identified recently: the porphyry-type, the skarn-type, the magmatic type, and volcanic/sedimentary-type. Tectonically, the development of these late Paleozoic gold and copper deposits was closely associated with the subduction and collision of the ancient Tianshan ocean that intervened between the Tarim craton and the Siberian block. In the early to mid-Carboniferous, N-dipping subduction beneath the Dananhu arc generated magmatic intrusions, leading to formation of the porphyry Cu deposits. The magmatic front migrated southward to form the Yamansu arc upon the Kanggurtag accretionary wedge. In the latest Carboniferous to early Permian, during the closure of the ancient Tianshan ocean, large mafic-ultramafic complexes were emplaced, resulting in several magmatic copper-nickel deposits. Gold deposits of the shear-zone-type are controlled by the Kanggurtag ductile shear zone, which is related to collisional orogenesis. The epithermal gold deposits are associated with extensional tectonics and post-tectonic volcanic activity. The tectonic settings, geological features, and temporal and spatial distributions of these different types of gold and copper deposits reflect, to a great extent, the accretionary and collisional tectonics that occurred between the northern margin of the Tarim block and the southern margin of the Siberian block. 相似文献
394.
Zhang Yunlin Qin Boqiang Zhu Guangwei Gao Guang Luo Liancong Chen Weimin 《中国科学D辑(英文版)》2006,49(1):114-125
Based on three continuous in situ underwater light field measurement under different wind waves conditions in Longgan Lake, Meiliang Bay of Taihu Lake in July 2003 and littoral zone near TLLER in July 2004, respectively, the effects of sediment resuspension caused by wind waves on PAR diffuse attenuation, absorption coefficients and euphotic depths are analyzed. In Longgan Lake, PAR diffuse attenuation coefficients during small, middle and large wind waves were 1.74, 2.02 and 2.45 m?1, respectively, and the corresponding PAR spectral diffuse attenuations ranged from 0.98 to 2.97, 1.34 to 3.95 and 1.80 to 5.40 m?1, respectively. In Meiliang Bay, PAR diffuse attenuation coefficients were 2.63, 3.72, 4.37 m?1 during small, middle and large wind waves. PAR diffuse attenuation coefficients increased by 41% and 66% from small to middle, large wind waves, respectively. Absorption coefficients integrated over the range of PAR of CDOM, phytoplankton were 0.26, 0.28 m?1; 0.76, 0.49 m?1, respectively during middle and large wind waves. Absorption coefficients integrated over the range of PAR of non-algal particulate matter and total suspended particulate matter increased from 0.94 to 1.73 m?1, and from 1.70 to 2.22 m?1, respectively during middle and large wind waves. Relative contributions of absorption coefficients of non-algal particulate matter to total absorption coefficient integrated over the range of PAR were 44.14%, 65.05%, respectively, during middle and large wind waves. PAR euphotic depths decreased by 0.40, 0.19, 0.20 m from middle to large wind waves in Longganhu Lake, Meliang Bay and littoral zone near TLLER. Significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and total suspended particulate matter, wind velocity, wave height. Most significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and inorganic suspended particulate matter but low correlations for chlorophyll a, dissolved organic carbon. Increase of total suspended particulate matter, especially inorganic suspended particulate matter caused by wind waves was the dominant factor affecting underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River based on observations at three stations. 相似文献
395.
396.
397.
多时相遥感影像辐射归一化方法综述 总被引:2,自引:0,他引:2
多时相遥感影像的辐射归一化是进行变化检测或拼接不可缺少的步骤。本文从绝对辐射归一化和相对辐射归一化两个方面对现有的多时相遥感影像辐射归一化方法进行了总结。对各种辐射归一化方法进行了剖析,并指出了这些方法的优缺点和适应性。最后对多时相遥感影像辐射归一化方法未来的发展进行了展望。 相似文献
398.
地面3维激光扫描仪是一种新型测量仪器,应用领域广泛。随着3维激光扫描技术和CCD传感器技术的不断发展,越来越多的3维激光扫描仪配有内置或者外置的数码相机。在对目标的描述上,点云和影像数据各有优势,扫描仪和数码相机的联合标定可为实现两者的优势互补提供基础。目前扫描仪和数码相机的联合标定主要是基于扫描区域的几何特性或者基于2维平面标定靶,这两种联合标定方法具有一定的局限性。这里在设计3维立体标定靶的基础上,提出了一种基于3维立体标定靶的联合标定方法。经过实验验证了联合标定方法的有效性和稳健性。 相似文献
399.
开垦对内蒙古温带草地土壤不同有机碳组分的影响(英文) 总被引:3,自引:2,他引:1
Cultivation is one of the most important human activities affecting the grassland ecosystem besides grazing, but its impacts on soil total organic carbon (C), especially on the liable organic C fractions have not been fully understood yet. In this paper, the role of cropping in soil organic C pool of different fractions was investigated in a meadow steppe region in Inner Mongolia of China, and the relationships between different C fractions were also discussed. The results indicated that the concentrations of different C fractions at steppe and cultivated land all decreased progressively with soil depth. After the conversion from steppe to spring wheat field for 36 years, total organic carbon (TOC) concentration at the 0 to 100 cm soil depth has decreased by 12.3% to 28.2%, and TOC of the surface soil horizon, especially those of 0-30 cm decreased more significantly (p<0.01). The dissolved organic carbon (DOC) and microbial biomass carbon (MBC) at the depth of 0-40 cm were found to have decreased by 66.7% to 77.1% and 36.5% to 42.4%, respectively. In the S.baicalensis steppe, the ratios of soil DOC to TOC varied between 0.52% and 0.60%, and those in the spring wheat field were only in the range of 0.18%-0.20%. The microbial quotients (qMBs) in the spring wheat field, varying from 1.11% to 1.40%, were also lower than those in the S. baicalensis steppe, which were in the range of 1.50%-1.63%. The change of DOC was much more sensitive to cultivation disturbance. Soil TOC, DOC, and MBC were significantly positive correlated with each other in the S. baicalensis steppe, but in the spring wheat field, the correlativity between DOC and TOC and that between DOC and MBC did not reach the significance level of 0.05. 相似文献
400.