全文获取类型
收费全文 | 5914篇 |
免费 | 617篇 |
国内免费 | 156篇 |
专业分类
测绘学 | 256篇 |
大气科学 | 641篇 |
地球物理 | 2176篇 |
地质学 | 2327篇 |
海洋学 | 320篇 |
天文学 | 504篇 |
综合类 | 189篇 |
自然地理 | 274篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 27篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2018年 | 469篇 |
2017年 | 413篇 |
2016年 | 287篇 |
2015年 | 183篇 |
2014年 | 154篇 |
2013年 | 145篇 |
2012年 | 682篇 |
2011年 | 463篇 |
2010年 | 159篇 |
2009年 | 179篇 |
2008年 | 148篇 |
2007年 | 149篇 |
2006年 | 145篇 |
2005年 | 846篇 |
2004年 | 896篇 |
2003年 | 669篇 |
2002年 | 194篇 |
2001年 | 92篇 |
2000年 | 56篇 |
1999年 | 28篇 |
1998年 | 20篇 |
1997年 | 25篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 5篇 |
1993年 | 13篇 |
1992年 | 5篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1983年 | 4篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1969年 | 5篇 |
1968年 | 4篇 |
1959年 | 3篇 |
1955年 | 5篇 |
1954年 | 3篇 |
排序方式: 共有6687条查询结果,搜索用时 15 毫秒
41.
42.
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
43.
44.
韧性剪切变形对岩石地球化学行为的制约——以北阿尔金巴什考供韧性剪切带为例 总被引:6,自引:0,他引:6
韧性剪切变形对岩石地球化学行为的制约一直是地质学家们探讨的课题。本文以构成北阿尔金红柳沟——拉配泉俯冲碰撞杂岩带与北阿尔金地块边界的巴什考供斜向逆冲型韧性剪切带为例,通过对韧性剪切带内花岗岩变形前后不同变形强度构造岩的地球化学组成进行对比,确定等比线斜率,探讨韧性变形对岩石体积和成分变异的影响。计算结果表明,在糜棱岩化过程中,糜棱岩化花岗岩体积亏损21%,花岗质糜棱岩体积亏损31%。质量平衡计算结果和等比线图表明,韧;陛剪切作用导致SiO2,流失量最大,A12O3、K2O及Ba、Rb、Sr等都有不同程度的丢失,显示出较强的活动性,MnO、P2O5、Sc位于等比线上或附近,表现出相对的稳定性。岩石中活动组分的变异是流体渗滤作用引起的,不活动组分的变异是体.积亏损造成的。 相似文献
45.
Paolo Canuti Nicola Casagli Filippo Catani Giacomo Falorni 《Physics and Chemistry of the Earth》2002,27(36):1587-1599
Lahars, here defined as debris flows of volcanic origin, are rapid mass movements that pose a serious threat to cities located in the vicinity of many volcanoes. Quito, capital city of Ecuador and placed at the foot of the Pichincha volcano complex, is exposed to serious inundation hazard as part of the city is built on numerous deposits of large lahars that have occurred in the last 10,000 years.The objective of this paper is to model the potential lahars of the Pichincha volcano to predict inundation areas within the city of Quito. For this purpose two models that apply different approaches were utilized and their results were compared.The programs used were LAHARZ, a semi-empirical model conceived by the United States Geological Survey (USGS), and FLO-2D, a hydraulic model distributed by FLO Software Inc. LAHARZ is designed as a rapid, objective and reproducible automated method for mapping areas of potential lahar inundation (Proc. First Int. Conf. on Debris Flow Hazards Mitigation, San Francisco, USA, ASCE, 1998, p. 176). FLO-2D is a two-dimensional flood routing model for simulating overland flow on complex surfaces such as floodplains, alluvial fans or urbanized areas (FLO-2D Users manual, version 99.2). Both models run within geographical information systems (GIS).Fieldwork was focused on collecting all available information involved in lahar modeling. A total of 49 channel cross-sections were measured along the two main streams and stratigraphic investigations were carried out on the fans to estimate the volume of previous events. A global positioning system was utilized to determine the coordinates of each cross-section. Further data collection concerned topography, rainfall characteristics and ashfall thicknesses. All fieldwork was carried out in cooperation with the Instituto Geofisico of the Escuela Politecnica Nacional.Modeling in a GIS environment greatly aided the exportation of results for the creation of thematic maps and facilitated model comparison. Evaluation of the models was performed by comparing simulation results against each other and against the geometry of existing lahar deposits. 相似文献
46.
新时期我国区域经济地理学发展问题初探 总被引:4,自引:0,他引:4
我国新时期的区域经济地理学在取得全面发展的同时,在理论体系,研究方法和实践领域等方面还需要进一步的发展,文章根据学习和实践区域经济地理学的体会,初步提出基础理论和应用理论,思维方法和技术方法等方面发展见解,并指出区域创新系统和国际经济技术合作等学科应注意拓展的重要实践领域,最后提出我国区域经济地理学科发展的建议。 相似文献
47.
48.
成都市民消费结构与休闲活动关系研究 总被引:6,自引:0,他引:6
城市居民消费水平,消费结构会影响其休闲消费能力,消费意愿,消费方式,消费态度和休闲时空结构,文章以成都市7个城区歌舞,茶棋牌,电影及城市公园休闲活动调查为基础,探讨了城市居民消费结构及其变化与休闲活动特征的关系。研究结果表明,城市居民消费结构的改变对歌舞,茶棋牌娱乐活动影响最大。 相似文献
49.
50.
区域视觉形象识别系统设计的理论与实践 总被引:6,自引:0,他引:6
目前,全国各地正在兴起区域形象设计与建设的浪潮,但如何把区域形象信息系统地传递出去,这方面的理论研究大大落后于实践。文章就区域形象信息传递的有效工具-区域视觉识别系统设计的主要内容,设计的原则,设计的基本流程等在理论与实践上作了较为详细的探讨,并就区域视觉识别系统设计方案的经济学论证作了一些有益探讨。 相似文献