全文获取类型
收费全文 | 7318篇 |
免费 | 1610篇 |
国内免费 | 2782篇 |
专业分类
测绘学 | 135篇 |
大气科学 | 403篇 |
地球物理 | 1677篇 |
地质学 | 7914篇 |
海洋学 | 443篇 |
天文学 | 73篇 |
综合类 | 431篇 |
自然地理 | 634篇 |
出版年
2024年 | 49篇 |
2023年 | 143篇 |
2022年 | 284篇 |
2021年 | 303篇 |
2020年 | 310篇 |
2019年 | 393篇 |
2018年 | 371篇 |
2017年 | 362篇 |
2016年 | 384篇 |
2015年 | 383篇 |
2014年 | 490篇 |
2013年 | 497篇 |
2012年 | 584篇 |
2011年 | 501篇 |
2010年 | 444篇 |
2009年 | 479篇 |
2008年 | 527篇 |
2007年 | 525篇 |
2006年 | 561篇 |
2005年 | 445篇 |
2004年 | 435篇 |
2003年 | 383篇 |
2002年 | 314篇 |
2001年 | 272篇 |
2000年 | 287篇 |
1999年 | 266篇 |
1998年 | 254篇 |
1997年 | 269篇 |
1996年 | 204篇 |
1995年 | 156篇 |
1994年 | 172篇 |
1993年 | 124篇 |
1992年 | 132篇 |
1991年 | 84篇 |
1990年 | 83篇 |
1989年 | 61篇 |
1988年 | 52篇 |
1987年 | 37篇 |
1986年 | 32篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
571.
572.
Hydraulic properties of the crystalline basement 总被引:1,自引:1,他引:1
Hydraulic tests in boreholes, up to 4.5 km deep, drilled into continental crystalline basement revealed hydraulic conductivity
(K) values that range over nine log-units from 10−13−10−4 m s−1. However, K values for fractured basement to about 1 km depth are typically restricted to the range from 10−8 to 10−6 m s−1. New data from an extended injection test at the KTB research site (part of the Continental Deep Drilling Program in Germany)
at 4 km depth provide K=5 10−8 m s−1. The summarized K-data show a very strong dependence on lithology and on the local deformation history of a particular area. In highly fractured
regions, granite tends to be more pervious than gneiss. The fracture porosity is generally saturated with Na–Cl or Ca–Na–Cl
type waters with salinities ranging from <1 to >100 g L−1. The basement permeability is well within the conditions for advective fluid and heat transport. Consequently, fluid pressure
is hydrostatic and a Darcy flow mechanism is possible to a great depth. Topography-related hydraulic gradients in moderately
conductive basement may result in characteristic advective flow rates of up to 100 L a−1 m−2 and lead to significant advective heat and solute transfer in the upper brittle crust.
An erratum to this article can be found at 相似文献
573.
江西安远路迳金伯利质煌斑岩筒研究——一种新型的幔源碱性超基性岩 总被引:1,自引:0,他引:1
路迳岩筒属火山通道相,由金伯利质煌斑岩、角砾岩、角砾凝灰岩组成,富含幔源橄榄岩包体、普通辉石巨晶和岩球。造岩矿物是橄榄石、斜方辉石、单斜辉石、角闪石和金云母,深源特征指示矿物有镁铝榴石、铬透辉石、铬尖晶石和镁钛铁矿。岩石化学组成超低SiO2,低MgO,高Al2O3,富碱,富挥发组分。轻稀土元素富集,相容元素贫化,不相容元素明显富集。岩浆起源深度约85km。其中:岩体产状,富含包体、巨晶和岩球,岩石结构和构造,矿物组成,岩石化学组成超低SiO2、富碱、富挥发组分等特征与金伯利岩相似;但岩石化学组成高Al2O3,低MgO,K2O低于Na2O,REE和LREE/HREE偏低,部分微量元素的亏损或富集,金云母成分富TiO2,富TFeO,贫MgO,镁铝榴石、铬透辉石、铬尖晶石和镁钛铁矿的Cr2O3含量偏低,岩浆起源深度较浅,均与金伯利岩有重大差异,而更接近煌斑岩类。研究认为,是幔源岩浆岩的一种新类型,岩石名称界定为金伯利质煌斑岩。 相似文献
574.
575.
In marine strata from Sinian to Middle Triassic in South China, there develop four sets of regional and six sets of local
source rocks, and ten sets of reservoir rocks. The occurrence of four main formation periods in association with five main
reconstruction periods, results in a secondary origin for the most marine gas pools in South China. To improve the understanding
of marine gas pools in South China with severely deformed geological background, the dominant control factors are discussed
in this paper. The fluid sources, including the gas cracked from crude oil, the gas dissolved in water, the gas of inorganic
origin, hydrocarbons generated during the second phase, and the mixed pool fluid source, were the most significant control
factors of the types and the development stage of pools. The period of the pool formation and the reconstruction controlled
the pool evolution and the distribution on a regional scale. Owing to the multiple periods of the pool formation and the reconstruction,
the distribution of marine gas pools was complex both in space and in time, and the gas in the pools is heterogeneous. Pool
elements, such as preservation conditions, traps and migration paths, and reservoir rocks and facies, also served as important
control factors to marine gas pools in South China. Especially, the preservation conditions played a key role in maintaining
marine oil and gas accumulations on a regional or local scale. According to several dominant control factors of a pool, the
pool-controlling model can be constructed. As an example, the pool-controlling model of Sinian gas pool in Weiyuan gas field
in Sichuan basin was summed up. 相似文献
576.
577.
Confidence intervals for earthquake source parameters 总被引:2,自引:0,他引:2
G. A. Prieto D. J. Thomson F. L. Vernon P. M. Shearer R. L. Parker 《Geophysical Journal International》2007,168(3):1227-1234
578.
579.