全文获取类型
收费全文 | 575篇 |
免费 | 47篇 |
国内免费 | 25篇 |
专业分类
测绘学 | 207篇 |
大气科学 | 43篇 |
地球物理 | 105篇 |
地质学 | 53篇 |
海洋学 | 27篇 |
天文学 | 2篇 |
综合类 | 51篇 |
自然地理 | 159篇 |
出版年
2023年 | 1篇 |
2022年 | 12篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 29篇 |
2016年 | 24篇 |
2015年 | 20篇 |
2014年 | 28篇 |
2013年 | 56篇 |
2012年 | 29篇 |
2011年 | 22篇 |
2010年 | 17篇 |
2009年 | 30篇 |
2008年 | 32篇 |
2007年 | 28篇 |
2006年 | 12篇 |
2005年 | 27篇 |
2004年 | 34篇 |
2003年 | 16篇 |
2002年 | 12篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有647条查询结果,搜索用时 15 毫秒
571.
Area coverage maximization in service facility siting 总被引:3,自引:2,他引:1
Traditionally, models for siting facilities in order to optimize coverage of area demand have made use of discrete space representations
to efficiently handle both candidate facility locations and demand. These discretizations of space are often necessary given
the linear functional forms of many siting models and the complexities associated with evaluating continuous space. Recently,
several spatial optimization approaches have been proposed to address the more general problem of identifying facility sites
that maximize regional coverage for the case where candidate sites and demand are continuously distributed across space. One
assumption of existing approaches is that only demand falling within a prescribed radius of the facility can be effectively
served. In many practical applications, however, service areas are not necessarily circular, as terrain, transportation, and
service characteristics of the facility often result in irregular shapes. This paper develops a generalized service coverage
approach, allowing a sited facility to have any continuous service area shape, not simply a circle. Given that demand and
facility sites are assumed to be continuous throughout a region, geometrical properties of the demand region and the service
facility coverage area are exploited to identify a facility site to optimize the correspondence between the two areas. In
particular, we consider the case where demand is uniformly distributed and the service area is translated to maximize coverage.
A heuristic approach is proposed for efficient model solution. Application results are presented for siting a facility given
differently shaped service areas.
相似文献
Alan T. MurrayEmail: |
572.
The nonsymmetry and antipacking pattern representation model(NAM) ,inspired by the concept of the packing problem,uses a set of subpatterns to represent an original pattern.The NAM is a promising method for image representation because of its ability to focus on the interesting subsets of an image.In this paper,we develop a new method for gray-scale image representation based on NAM,called NAM-structured plane decomposition(NAMPD) ,in which each subpattern is associated with a rectangular region in the imag... 相似文献
573.
面向地理问题求解的数据表达模型研究 总被引:1,自引:1,他引:0
本文以地理问题求解和地理科学研究建模环境建设的需求为导向,针对面向地理问题求解建模环境在利用多源异构数据方面遇到的问题,进行了面向地理问题求解的数据表达模型(XGE-DRM)的研究。本文重点研究了多源、异构、跨领域地理数据的表达方式与组织规范,从原子数据层与对象组织层两个层次对XGE-DRM的基本原子构成与对象组成方式进行了阐述;通过对地理数据的结构与语义进行解析,显式表达地理数据的结构与语义;在结构清晰、语义明确的情况下,实现多源异构数据的抽取与交换,最终实现多源异构数据的共享。实验证明,文中提出的数据表达模型能够实现多源异构数据的通用表达,解决地理问题求解建模环境平台下数据共享的问题。 相似文献
574.
The present work contributes to the debate of skeletal part use in archaeology to reconstruct hominid economic behaviour during the Pleistocene. It doubles the sample of sites where comparison of long limb bone element quantification is made by using alternative identification techniques based on epiphyses and epiphyses plus shafts. A refined method of long limb element quantification using shafts is discussed and applied to four sites representing different time periods from the end of the Middle Pleistocene to the end of the Upper Pleistocene. It is shown that when long limb elements are properly quantified a hypothesis of early access to carcasses at these sites can be supported. The data thus drawn are also used to compare skeletal part evenness across the time periods represented by the four sites selected. The results indicate low‐cost transport decisions by hominids at these sites. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
575.
576.
The subject of the investigation was the multiyear hindcast of the sea level elevations and currents over the Baltic Sea. The approach follows to the HIPOCAS project conception and contained the 3D hydrodynamic model using boundary conditions from the atmosphere and catchment for 44-year period referring to the second half of the 20th century. 相似文献
577.
The aim of this study was to identify potential environmental “key factors” causing spatial distributions of macrozoobenthic communities to improve our understanding concerning benthic biotic/abiotic interactions and ecosystem functioning. To this end benthic and environmental data, collected over a period of 4 years (2003–2006) at 191 sampling stations in the Pomeranian Bay (southwest Baltic Sea), were analysed. This represents the most comprehensive study performed in this respect in the Baltic Sea up to date and also the necessary first step towards a model able to predict macrofaunal distributions regarding autecological species-environment interactions. Based on species abundances, distinctive macrobenthic community patterns were identified and evaluated via univariate correlation methods, multivariate numerical classification and ordination techniques (e.g. PCA, CCA). These patterns were caused by clear responses of several benthic species to certain prevailing environmental conditions. The observed distribution of selected species followed a strong gradient of depth and was explained best by the sediment parameters total organic carbon (TOC), median grain size and sorting. By using different statistical methods these abiotic/biotic interactions were modelled allowing to extend our knowledge concerning ecosystem functioning, and provide a tool to assess natural and anthropogenic forced changes in species distribution. 相似文献
578.
579.
580.