全文获取类型
收费全文 | 11086篇 |
免费 | 1710篇 |
国内免费 | 1607篇 |
专业分类
测绘学 | 767篇 |
大气科学 | 1493篇 |
地球物理 | 3256篇 |
地质学 | 5455篇 |
海洋学 | 1010篇 |
天文学 | 672篇 |
综合类 | 675篇 |
自然地理 | 1075篇 |
出版年
2024年 | 34篇 |
2023年 | 103篇 |
2022年 | 268篇 |
2021年 | 356篇 |
2020年 | 265篇 |
2019年 | 351篇 |
2018年 | 751篇 |
2017年 | 697篇 |
2016年 | 588篇 |
2015年 | 480篇 |
2014年 | 440篇 |
2013年 | 501篇 |
2012年 | 964篇 |
2011年 | 777篇 |
2010年 | 461篇 |
2009年 | 472篇 |
2008年 | 497篇 |
2007年 | 446篇 |
2006年 | 365篇 |
2005年 | 1080篇 |
2004年 | 1112篇 |
2003年 | 888篇 |
2002年 | 489篇 |
2001年 | 360篇 |
2000年 | 258篇 |
1999年 | 224篇 |
1998年 | 146篇 |
1997年 | 179篇 |
1996年 | 129篇 |
1995年 | 105篇 |
1994年 | 83篇 |
1993年 | 76篇 |
1992年 | 84篇 |
1991年 | 50篇 |
1990年 | 54篇 |
1989年 | 44篇 |
1988年 | 42篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 5篇 |
1958年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The Menilite Shales (Oligocene) of the Polish Carpathians are the source of low-sulfur oils in the thrust belt and some high-sulfur oils in the Carpathian Foredeep. These oil occurrences indicate that the high-sulfur oils in the Foredeep were generated and expelled before major thrusting and the low-sulfur oils in the thrust belt were generated and expelled during or after major thrusting. Two distinct organic facies have been observed in the Menilite Shales. One organic facies has a high clastic sediment input and contains Type-II kerogen. The other organic facies has a lower clastic sediment input and contains Type-IIS kerogen. Representative samples of both organic facies were used to determine kinetic parameters for immiscible oil generation by isothermal hydrous pyrolysis and S2 generation by non-isothermal open-system pyrolysis. The derived kinetic parameters showed that timing of S2 generation was not as different between the Type-IIS and -II kerogen based on open-system pyrolysis as compared with immiscible oil generation based on hydrous pyrolysis. Applying these kinetic parameters to a burial history in the Skole unit showed that some expelled oil would have been generated from the organic facies with Type-IIS kerogen before major thrusting with the hydrous-pyrolysis kinetic parameters but not with the open-system pyrolysis kinetic parameters. The inability of open-system pyrolysis to determine earlier petroleum generation from Type-IIS kerogen is attributed to the large polar-rich bitumen component in S2 generation, rapid loss of sulfur free-radical initiators in the open system, and diminished radical selectivity and rate constant differences at higher temperatures. Hydrous-pyrolysis kinetic parameters are determined in the presence of water at lower temperatures in a closed system, which allows differentiation of bitumen and oil generation, interaction of free-radical initiators, greater radical selectivity, and more distinguishable rate constants as would occur during natural maturation. Kinetic parameters derived from hydrous pyrolysis show good correlations with one another (compensation effect) and kerogen organic-sulfur contents. These correlations allow for indirect determination of hydrous-pyrolysis kinetic parameters on the basis of the organic-sulfur mole fraction of an immature Type-II or -IIS kerogen. 相似文献
132.
Histograms of observations from spatial phenomena are often found to be more heavy-tailed than Gaussian distributions, which
makes the Gaussian random field model unsuited. A T-distributed random field model with heavy-tailed marginal probability density functions is defined. The model is a generalization
of the familiar Student-T distribution, and it may be given a Bayesian interpretation. The increased variability appears cross-realizations, contrary
to in-realizations, since all realizations are Gaussian-like with varying variance between realizations. The T-distributed random field model is analytically tractable and the conditional model is developed, which provides algorithms
for conditional simulation and prediction, so-called T-kriging. The model compares favourably with most previously defined random field models. The Gaussian random field model
appears as a special, limiting case of the T-distributed random field model. The model is particularly useful whenever multiple, sparsely sampled realizations of the
random field are available, and is clearly favourable to the Gaussian model in this case. The properties of the T-distributed random field model is demonstrated on well log observations from the Gullfaks field in the North Sea. The predictions
correspond to traditional kriging predictions, while the associated prediction variances are more representative, as they
are layer specific and include uncertainty caused by using variance estimates. 相似文献
133.
区域经济协调发展是国民经济发展的客观要求,关系到整个国民经济的战略全局。西部大开发是区域经济协调发展的内在要求和具体体现。非均衡区域经济理论是西部大开发与区域经济协调发展这一重大实践问题的核心理论,我国西部地区以其丰富的资源优势及潜在的区位优势已成为中国经济持续、快速、健康发展的新的增长点。 相似文献
134.
135.
136.
CHENGPenggen SHIWenzhong GONGJianya ZHOUGuoqing 《地球空间信息科学学报》2005,8(1):64-71
3D spatial data model and simulating are the core of 3D GIS can be adopted in different domains. A data model based on Quasi Tri-Prism Volume (QTPV) has been proposed. QTPV definition and its special cases have been discussed. Using QTPV and its special cases, irregular natural geological bodies and regular subsurface engineering can be described efficiently. The proposed model is composed of five primitives and six objects. Data structures and topological relationship of the fives primitives and three objects describing stratigraphy are designed in detail Some schemes are designed for the QTPV modelling of stratigraphy and subsurface engineering according to modelling data. The model manipulation method of QTPV cutting by an arbitrary plane is discussed. Using VC 6.0 programming language integrated with SQL database and OpenGL graphic library under windows environment, a system prototype 3DGeoMV has been developed. The experiment result shows that the QTPV model is feasible and efficient in modelling subsurface engineering. 相似文献
137.
地理信息共享与GIS互操作是社会化GIS时代地理信息技术发展的必然趋势。本文在简述地理信息共享及GIS互操作理论的基础上,分析了基于Web服务的信息生命周期和OGC提出的OpenGIS服务架构,最后提出了西南资源环境信息共享与服务平台的初步架构。 相似文献
138.
陕西省地质灾害气象预报预警系统的应用与现状 总被引:1,自引:0,他引:1
从降水这一诱发地质灾害的关键因素入手,在对陕西省地质灾害分布规律及其与气象条件关系研究分析的基础上,确定不同区域不同降雨强度诱发地质灾害的临界值,建立了陕西省地质灾害气象预报预警系统。根据降雨量等级,利用神经网络算法,划分地质灾害预报预警等级,进行有效的防灾预报。 相似文献
139.
140.