全文获取类型
收费全文 | 2321篇 |
免费 | 596篇 |
国内免费 | 896篇 |
专业分类
测绘学 | 213篇 |
大气科学 | 66篇 |
地球物理 | 821篇 |
地质学 | 1792篇 |
海洋学 | 348篇 |
天文学 | 4篇 |
综合类 | 195篇 |
自然地理 | 374篇 |
出版年
2024年 | 14篇 |
2023年 | 34篇 |
2022年 | 71篇 |
2021年 | 104篇 |
2020年 | 123篇 |
2019年 | 138篇 |
2018年 | 113篇 |
2017年 | 114篇 |
2016年 | 150篇 |
2015年 | 140篇 |
2014年 | 200篇 |
2013年 | 172篇 |
2012年 | 179篇 |
2011年 | 176篇 |
2010年 | 165篇 |
2009年 | 213篇 |
2008年 | 188篇 |
2007年 | 183篇 |
2006年 | 168篇 |
2005年 | 146篇 |
2004年 | 137篇 |
2003年 | 112篇 |
2002年 | 87篇 |
2001年 | 73篇 |
2000年 | 85篇 |
1999年 | 73篇 |
1998年 | 66篇 |
1997年 | 69篇 |
1996年 | 63篇 |
1995年 | 59篇 |
1994年 | 33篇 |
1993年 | 29篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 15篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有3813条查询结果,搜索用时 296 毫秒
41.
The Glueckstadt Graben of the North-German Basin: new insights into the structure from 3D and 2D gravity analyses 总被引:1,自引:0,他引:1
Tamara Yegorova Yuriy Maystrenko Ulf Bayer Magdalena Scheck-Wenderoth 《International Journal of Earth Sciences》2008,97(5):915-930
The structure of the Glueckstadt Graben has been investigated by use of 3D gravity backstripping technique and by 2D gravity
and magnetic modelling. Subtracting the gravity effects of the Meso-Cenozoic sediments together with Permian salt reveals
a positive residual anomaly within the Glueckstadt Graben. This anomaly includes two local maxima over the Westholstein and
Eastholstein Troughs. The 2D gravity models point to the presence of a high-density body within the lower crust of the Glueckstadt
Graben. In addition, the results of 2D magnetic modelling indicate that the central part of the high-density body is overlain
by an area with high susceptibility. Most probable, the formation of this high-density body is a result of complex poly-phase
tectonic history of the study area. Finally, the results of gravity modelling indicate that Permian salt is not homogeneous.
3D gravity analysis and, especially, 2D gravity modelling have distinguished the differences in degree of salt saturation
in salt-rich bodies, and elucidate the proportion of Rotliegend salt. 相似文献
42.
The 2004 Chuetsu earthquakes of Niigata (Japan) triggered numerous landslides, and the most widespread types of landslides
were highly disrupted, relatively shallow slides and soil (debris) flows. This paper presented a method to evaluate slope
instability using Newmark displacement on a pixel-by-pixel basis in a given area. The proposed method was able to integrate
Newmark displacement modeling and Monte Carlo simulations within geographical information systems. In the modeling, an empirical
attenuation relationship was utilized to calculate Arias intensity over this study area, and the variability of geotechnical
parameters was taken into account to calculate coseismic landslide displacement. Before deriving the displacement from related
inputs, the Monte Carlo simulations ran 1,500 times and generated 1,500 displacement values for each grid cell, and then means
and standard deviations of displacement were calculated and probabilistic distributions can be obtained. Finally, given 10 cm
as a threshold value of displacement, estimated probabilities of displacement exceeding 10 cm were shown as a map of seismic
landslide hazards. The resulting hazard map was classified into four categories from very low to high level. 相似文献
43.
44.
西藏扎布耶盐田盐渍土的改性配比试验 总被引:1,自引:0,他引:1
根据盐渍土的物理化学性质,采用掺入不同比例石灰或水泥的方法进行改性处理。经击实、抗剪和抗压强度试验结果表明,盐渍土掺入石灰或水泥改性后,混合料的最大干密度、最优含水率、强度指标等均有增加,特别是内聚力迅速增长。研究表明,盐渍土混合料的性状得到了明显改善,改性后的混合料可用于修建盐田埝堤类相关工程。 相似文献
45.
46.
Definition and measurement of salinity in salt lakes 总被引:4,自引:0,他引:4
Salinity is the most important chemical attribute of athalassic salt lakes. Even so, some confusion persists of what salinity means and how to measure it. For sal lakes, salinity is best defined as the sum total of all ion concentrations, or total ion concentration. Ideally, it is recommended that salinities be expressed on a mass per mass basis and as ppt (parts per thousand). Direct measurements of salinity can only be derived from full ionic analyses. Indirect measurements can be derived by determinations of density, conductivity, freezing point depression and total dissolved solids or matter. 相似文献
47.
新疆第四纪盐类矿产的形成和控制因素——兼论“高山深盆”成盐模式 总被引:1,自引:0,他引:1
根据袁见齐教授“高山深盆”成盐模式,探讨新疆天山对第四纪盐类矿床的形成和控制作用,阐述了天山地貌、气候、水文特征与盐类矿产的分布规律和特征。认为“高山深盆”并非一定是四周环山的深盆,可以是某一高山与其间深盆或两侧盆地的有机组合。高山的屏障作用造成了垂直的气候分带,在潮湿多雨的山区利于成盐组份的析出并迁移到干旱少雨的闭流深盆中,形成盐类矿床。 相似文献
48.
49.
The zooplankton of two salt ponds at Aveiro was studied to evaluate its density and diversity. Samples were collected biweekly from the salt ponds Esmolas and Tanoeiras. Samples were first separated into Holoplankton (Copepoda, nauplii,Acartia, Ostracoda and Anostraca) and Meroplankton (Mollusca, Insecta, annelidan larvae and Ichthyoplankton). The Holoplankton was mainly composed of:Acartia tonsa, Acartia sp.,Eurytemora velox, Artemia sp., and harpacticoids and calanoids. In both salt ponds, species diversity was identical, but total zooplankton density was higher in the Tanoeiras salt pond, probably because its physical and chemical characteristics allowed the development of stable communities. 相似文献
50.