首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   580篇
  免费   96篇
  国内免费   31篇
测绘学   44篇
大气科学   45篇
地球物理   253篇
地质学   182篇
海洋学   27篇
天文学   14篇
综合类   26篇
自然地理   116篇
  2024年   2篇
  2023年   6篇
  2022年   19篇
  2021年   12篇
  2020年   18篇
  2019年   36篇
  2018年   14篇
  2017年   19篇
  2016年   27篇
  2015年   27篇
  2014年   21篇
  2013年   50篇
  2012年   24篇
  2011年   25篇
  2010年   22篇
  2009年   31篇
  2008年   34篇
  2007年   30篇
  2006年   40篇
  2005年   41篇
  2004年   27篇
  2003年   22篇
  2002年   22篇
  2001年   18篇
  2000年   14篇
  1999年   12篇
  1998年   16篇
  1997年   13篇
  1996年   13篇
  1995年   14篇
  1994年   7篇
  1993年   7篇
  1992年   6篇
  1991年   1篇
  1990年   3篇
  1989年   4篇
  1988年   3篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   2篇
  1980年   1篇
  1954年   1篇
排序方式: 共有707条查询结果,搜索用时 0 毫秒
51.
云南地区地震序列分类的定量讨论   总被引:1,自引:0,他引:1  
本文通过对云南地区1965提以来116次大小地震序列的清理和归纳,引入了地震序列分类的时空强定量尺度,提出;表明震源区进人失稳状态的前震序列主要发生在主震前10天,前震序列的最大震级5.5级;震群型地震序列在时间、地点上的确定应与震级有关,在时间上以同在地震孕期内为宜,7、6、5级分别不超过1年、半年、3个月,在地点上以同在地震孕震区内为2,7、6、5级分别不超过100、50、30公里,震级上以小子等于0.5级为宜;主余震地震序列和孤立型地震序列的最大震级差分别是2.9级和3.3级  相似文献   
52.
Research on scale effect of histogram   总被引:2,自引:0,他引:2  
To describe the spatial relationship among the earth objects compactly, in this paper, we raised the concept of histo-variogram based on the analysis of the characteristics of other spatial analyzing methods such as variogram, information entropy. And we also raised a new spatial analysis method of histogram decomposition based on the definition of standing pixel and contour pixel. At the end of this paper, we demonstrated the characteristics of histo-variogram by two experiments, one for spatial analysis, the other for image fusion.  相似文献   
53.
High-resolution temporal rainfall data sequences serve as inputs for a range of applications in planning, design and management of small (especially urban) water resources systems, including continuous flow simulation and evaluation of alternate policies for environmental impact assessment. However, such data are often not available, since their measurements are costly and time-consuming. One alternative to obtain high-resolution data is to try to derive them from available low-resolution information through a disaggregation procedure. This study evaluates a random cascade approach for generation of high-resolution rainfall data at a point location. The approach is based on the concept of scaling in rainfall, or, relating the properties associated with the rainfall process at one temporal scale to a finer-resolution scale. The procedure involves two steps: (1) identification of the presence of scaling behavior in the rainfall process; and (2) generation of synthetic data possessing same/similar scaling properties of the observed rainfall data. The scaling identification is made using a statistical moment scaling function, and the log–Poisson distribution is assumed to generate the synthetic rainfall data. The effectiveness of the approach is tested on the rainfall data observed at the Sydney Observatory Hill, Sydney, Australia. Rainfall data corresponding to four different successively doubled resolutions (daily, 12, 6, and 3 h) are studied, and disaggregation of data is attempted only between these successively doubled resolutions. The results indicate the presence of multi-scaling behavior in the rainfall data. The synthetic data generated using the log–Poisson distribution are found to exhibit scaling behaviors that match very well with that for the observed data. However, the results also indicate that fitting the scaling function alone does not necessarily mean reproducing the broader attributes that characterize the data. This observation clearly points out the extreme caution needed in the application of the existing methods for identification of scaling in rainfall, especially since such methods are also prevalent in studies of the emerging satellite observations and thus in the broader spectrum of hydrologic modeling.  相似文献   
54.
This study examines alpine soil development along a toposequence on Eagle Cap, Wallowa Mountains, northeast Oregon. Soils studied are from Wind Blown (WB) and Minimal Snow Cover (MSC) sites in the Ridge-Top Tundra geomorphic province. The soils are predominantly loamy sands, and exhibit minimal structural development. Soil pH ranges from 6.5 to 7.3 increasing with depth, and organic carbon ranges from 3.9% in the A horizon to 0.8% in the C horizon. The soils display significant input from Cascade volcanic ash infall and eolian influx from the weathered marble nearby. It is postulated that the ash content in the soils originates from Mazama Ash deposits. Though Eagle Cap soils have developed for the most part on granodiorite, the strong influence of the volcanic ash on pedogenesis leads to a preliminary classification of Andisols, most probably Typic and Lithic Haplocryands. [Key words: Alpine soils, Andisols, Wallowa Mountains.]  相似文献   
55.
《自然地理学》2013,34(2):137-154
Floristic composition and environmental factors vary widely among plant communities in the alpine belt. Thus far no study has attempted to measure all relevant site conditions in a larger number of alpine communities. Here we show (1) which environmental factors were highly correlated with the floristic composition of the 14 plant communities investigated in the Swiss Alps and (2) which plant communities have similar environmental affinities. In every plant community investigated, the main factors potentially having an impact on plant life were measured and the floristic composition was defined. We used nonmetric multidimensional scaling (NMDS) to determine linkage between plant communities and complex environmental gradients. The first axis of the NMDS corresponds to a climate gradient (temperature/wind speed), and the second axis corresponds to a soil gradient (soil suction/pH/Ca content). With the exception of the Nardus grassland and Carex curvula turf, plant communities belonging to the same phytosociological class are exposed to very similar combinations of environmental factors. Our study shows that the variation between phytosociological classes is much larger than within classes. Still, the variation of environmental factors within individual classes leads to a further differentiation of the floristic composition. Thus, our study reinforces the validity of the phytosociological classification.  相似文献   
56.
用综合信息矿产资源定量预测的理论和方法,系统研究了辽宁水泉金矿成矿规律及控矿因素,特别是对控矿构造特征作了深入的研究,并建立了研究区的综合信息找矿模型。对水泉金矿的区域成矿远景和深部成矿远景进行了综合预测。  相似文献   
57.
An infinity of conservation laws of fKdV equation is derived in terms of the Miura and Gardner''s transform.The pseudo-mass and energy theorems are studied by the first two conservation laws.As a typical example,the theoretical mean wave resistance and the regional distribution of energy of the precursor soliton generation are determined by means of the first and the second conservation laws.  相似文献   
58.
59.
This paper evaluates a recent record selection and scaling procedure of the authors that can determine the probabilistic structural response of buildings behaving either in the elastic or post‐elastic range. This feature marks a significant strength on the procedure as the probabilistic structural response distribution conveys important information on probability‐based damage assessment. The paper presents case studies that show the utilization of the proposed record selection and scaling procedure as a tool for the estimation of damage states and derivation of site‐specific and region‐specific fragility functions. The method can be used to describe exceedance probabilities of damage limits under a certain target hazard level with known annual exceedance rate (via probabilistic seismic hazard assessment). Thus, the resulting fragility models can relate the seismicity of the region (or a site) with the resulting building performance in a more accurate manner. Under this context, this simple and computationally efficient record selection and scaling procedure can be benefitted significantly by probability‐based risk assessment methods that have started to be considered as indispensable for developing robust earthquake loss models. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
60.
Considering the existing problems of the petroleum system, this paper brings forward the concept of natural gas accumulation system and presents the dividing principles. Then detailed statistics on the accumulation factors of the 32 typical natural gas accumulation systems in China and studies on the laws controlling distribution of gas are collected. The research shows that the petroleum accumulation system is the basic unit controlling petroleum generation, migration and accumulation. Generating intensity, generating amount, accumulating efficiency and migration distance plays an important role in the distribution of natural gas. Through analysis on results of resources evaluation, discovered reserves and residual reserves, potential areas in middle-scaled petroliferous basins in China are forecasted in this paper. Ordos, Sichuan, Tarim and Qaidam basins are found out to be the main basins developing and enriching gas accumulation systems.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号