全文获取类型
收费全文 | 4396篇 |
免费 | 831篇 |
国内免费 | 1119篇 |
专业分类
测绘学 | 297篇 |
大气科学 | 810篇 |
地球物理 | 913篇 |
地质学 | 2157篇 |
海洋学 | 333篇 |
天文学 | 34篇 |
综合类 | 292篇 |
自然地理 | 1510篇 |
出版年
2024年 | 24篇 |
2023年 | 83篇 |
2022年 | 181篇 |
2021年 | 204篇 |
2020年 | 217篇 |
2019年 | 258篇 |
2018年 | 207篇 |
2017年 | 221篇 |
2016年 | 225篇 |
2015年 | 242篇 |
2014年 | 278篇 |
2013年 | 303篇 |
2012年 | 290篇 |
2011年 | 270篇 |
2010年 | 229篇 |
2009年 | 314篇 |
2008年 | 271篇 |
2007年 | 247篇 |
2006年 | 271篇 |
2005年 | 242篇 |
2004年 | 229篇 |
2003年 | 204篇 |
2002年 | 179篇 |
2001年 | 174篇 |
2000年 | 137篇 |
1999年 | 114篇 |
1998年 | 127篇 |
1997年 | 94篇 |
1996年 | 109篇 |
1995年 | 92篇 |
1994年 | 70篇 |
1993年 | 56篇 |
1992年 | 49篇 |
1991年 | 23篇 |
1990年 | 27篇 |
1989年 | 15篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有6346条查询结果,搜索用时 484 毫秒
281.
中长期地震预测方案综合信度评价的层次分析法 总被引:4,自引:3,他引:4
由于存在各种复杂的不确定因素的影响,正确合理地评价地震观测结果的可信度,具有一定的难度。本文首先引入具有广泛应用途的层次分析法,并以华北北部为例,结合Delphi专家咨询结果,给出了反映各个预测方案结果的可信度及具有满意一致性的相对重要性权系数。其结果可作为综合各种预测方案,确定该地区中长期地震危险区的参考依据。 相似文献
282.
气温长期演变趋势中城市化的可能影响 总被引:5,自引:0,他引:5
利用兰州、上海及其周围站点的1月和年平均气温资料,通过对比,分析了城市化对气温长度演变趋势的影响。结果表明在区域性气候增暖过程中,城市化的影响是不可忽略的。 相似文献
283.
Abstract The Nankai Trough, off southwest Japan, is one of the best sites for the study of geomorphic characteristics of a clastic accretionary prism. A recent multibeam survey over the central and eastern parts of the Nankai accretionary prism has revealed a large variation of the topography along the trough axis. Analysis of the bathymetric data suggests the existence of prism deformational features of different scales, such as depressions, embayment structures and cusps. These structures are the results of slope instability caused by basement relief of subducted oceanic plate. Unstable slopes recover by new accretion and development of a low angle thrust. Small-scale deformation due to the subduction of a small isolated seamount is then adjusted to the regional trend. By contrast, a 30 km indentation of the wedge observed in the eastern part of the Nankai Trough, the Tenryu Cusp, has seemed to retain its geometry. The subducted Philippine Sea plate has deformed greatly near the eastern end of the Nankai Trough, because of the collision between the Izu-Ogasawara (Bonin) arc and central Japan. Therefore, the indentation may be the result of the continuous subduction of a basement high, such as the Zenisu Ridge, which has been formed under north-south compression due to the arc-arc collision. 相似文献
284.
285.
Very little work has been done in generating alternatives to the Poisson process model. The work reported here deals with
alternatives to the Poisson process model for the earthquakes and checks them using empirical data and the statistical hypothesis
testing apparatus. The strategy used here for generating hypotheses is to compound the Poisson process. The parameter of the
Poisson process is replaced by a random variable having prescribed density function. The density functions used are gamma,
chi and extended (gamma/chi). The original distribution is then averaged out with respect to these density functions. For
the compound Poisson processes the waiting time distributions for the future events are derived. As the parameters for the
various statistical models for earthquake occurrences are not known, the problem is basically of composite hypothesis testing.
One way of designing a test is to estimate these parameters and use them as true values. Momentmatching is used here to estimate
the parameters. The results of hypothesis testing using data from Hindukush and North East India are presented. 相似文献
286.
Intensive water sampling in conjunction with hydrological observations was conducted during three different rainstorms in order to understand the effects of rainfall events on the temporal variation of streamwater chemistry in a small headwater forest catchment. Concentrations of Na+ and SO42? decreased as the discharge rate increased. Hydrograph separation of the components was made using the three‐component model based on the end‐members mixing analysis (EMMA). The three end‐members were:
- 1 the groundwater in the saturated zone that prescribes the chemistry of the baseflow;
- 2 the throughfall that dilutes the streamwater;
- 3 the groundwater in the transient saturated zone prescribed, which was dependent on the groundwater level.
287.
Allocating local groundwater monitoring stations for South Korea using an analytic hierarchy process 总被引:1,自引:1,他引:1
Jeong-Woo Kim Jin-Yong Lee Myeong-Jae Yi Gyoo-Bum Kim Jong-Ho Won Kang-Kun Lee 《Hydrogeology Journal》2007,15(3):615-632
A national groundwater-monitoring network consisting of 320 stations has been operated by the Ministry of Construction and Transportation and the Korea Water Resources Corporation since 1995. The network was established as a result of the Groundwater Act of Korea, and a supplementary local groundwater monitoring network containing 10,000 stations will be established throughout the country by the year 2011. A method of allocating stations and organizing the local monitoring network has been developed, based on the analytic hierarchy process (AHP), using pairwise comparison. Several evaluation criteria were selected for determining the required number of the monitoring stations at specific local districts. Weights of the selected criteria were assigned by the pairwise comparison, reflecting hydrogeological conditions and supported by pertinent questions to 93 groundwater experts. To evaluate appropriateness of this method, an example city, Jeonju, was selected where groundwater levels were monitored; seven stations were determined as to be required for the supplementary groundwater-monitoring network. The study demonstrated the usefulness of the AHP. The concepts of the development and the structure of the AHP model can be applied to site or well selections within a particular district. 相似文献
288.
云南民族地区城市化与产业集群关系的研究 总被引:1,自引:0,他引:1
云南民族地区作为欠发达地区,在发展的过程中面临着很多的问题,这些问题无一不与城市化密切相关,而产业集群作为一种新的经济发展模式,显现出了它独特的优势,所以正确认识产业集群与城市化的互动关系,是云南民族区域要实现区域的协调发展的关键.产业集群与城市化是耦合发展的,在分析云南民族地区产业集群与城市化互动发展现状的基础上,云南必须选择符合自身发展的互动发展模式,最后提出云南城市化发展与产业集群互动发展的政策建议. 相似文献
289.
高山树线交错带的景观格局与生态过程 总被引:1,自引:1,他引:1
由于对气候变化的敏感性, 近年来高山树线交错带成为全球变化研究中的热点问题。高 山树线交错带所指示的是一个复杂生态系统的特征, 反映出了由低处植被向高山植被的转化, 其 景观格局是综合了种子定居, 树木生长以及树木繁殖等多个树木生态过程和特定高山环境下的 地理特征格局的适应结果。一方面, 树木通过自身生理生态学上的调整对高山极端环境进行适 应。一方面, 高山特定地理环境特征对树线的景观格局进行影响, 因而高山树线交错带成为研究 景观格局- 生态过程相互关系的一个重要载体。通过运用3S 技术, 可以将高山树线交错带研究中 的树线景观结构和生理生态过程结合在一起, 并验证在其景观格局形成过程中地理特征和人为 因子的相对重要性。 相似文献
290.
建设新农村与城镇化的关系初探 总被引:1,自引:0,他引:1
如何正确处理新农村建设和城镇化的关系,是一个值得深入探讨的问题。中国城市化进程应是以区域一体化为中心的城市化道路,乡村发展也是城镇化的内容。从中国的实情出发,要重新认识“二元经济”理论,“二元经济”的模型是以粮食代表整个农业生产。城镇化和建设新农村在组织形式上存在差异区别,但不存在严重的资金竞争,并且在服务对象、功能、产业结构方面是互补的,城镇化和建设新农村是并行不悖的,城镇化与建设新农村可以在很长时间内共同发展。 相似文献