全文获取类型
收费全文 | 3836篇 |
免费 | 435篇 |
国内免费 | 522篇 |
专业分类
测绘学 | 1323篇 |
大气科学 | 313篇 |
地球物理 | 607篇 |
地质学 | 1183篇 |
海洋学 | 315篇 |
天文学 | 61篇 |
综合类 | 334篇 |
自然地理 | 657篇 |
出版年
2024年 | 29篇 |
2023年 | 68篇 |
2022年 | 139篇 |
2021年 | 181篇 |
2020年 | 222篇 |
2019年 | 207篇 |
2018年 | 142篇 |
2017年 | 215篇 |
2016年 | 198篇 |
2015年 | 205篇 |
2014年 | 173篇 |
2013年 | 266篇 |
2012年 | 212篇 |
2011年 | 207篇 |
2010年 | 156篇 |
2009年 | 202篇 |
2008年 | 213篇 |
2007年 | 241篇 |
2006年 | 216篇 |
2005年 | 147篇 |
2004年 | 139篇 |
2003年 | 135篇 |
2002年 | 114篇 |
2001年 | 86篇 |
2000年 | 87篇 |
1999年 | 81篇 |
1998年 | 77篇 |
1997年 | 70篇 |
1996年 | 58篇 |
1995年 | 44篇 |
1994年 | 52篇 |
1993年 | 47篇 |
1992年 | 36篇 |
1991年 | 15篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1973年 | 7篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有4793条查询结果,搜索用时 15 毫秒
1.
Mark D. Schwartz 《The Professional geographer》1991,43(1):77-91
Both subjective and objective schemes for air mass classification offer advantages to climatological studies. An integrated approach is developed and applied to 850 mb level data in the north central United States. Each air mass type was initially delimited by a subjective analysis. Final limits were then determined with an objective technique that separates temperature curves into normal components based on interpretation from the subjective method. Continental air was most frequent in all seasons except summer. The methodology also allows estimation of classification error. 相似文献
2.
Dan Gill 《Mathematical Geology》1993,25(4):471-482
The ability of association analysis to discriminate sedimentary facies was tested on Purdy's modal analyses of modern sediments of the Great Bahama Bank. Purdy's data set has served in the past as a standard reference for evaluating various multivariate classification algorithms. In order to adapt Purdy's data to association analysis, the percent abundance of the 12 constituents was converted to binary form by dichotomizing each variable on its mean value. The results obtained by association analysis are virtually identical to those obtained by Purdy and other authors. The same four main sedimentary facies were discriminated; 86% of the samples were identically classified (97% when misclassified borderline cases are counted as matches); the total partition variance of the classification is only negligibly greater (4%); and the grouping of the variables yielded the same four groups. The rank order of the three division-attributes responsible for the sample classification is fines, oolites, and corals. Association analysis has been employed by other authors to differentiate meaningful facies groups in studies of ancient reef carbonates, modern reef sediments, and heavy minerals in stream sediments. In all these studies, the results were found to be compatible with those obtained by using the continuous quantitative measurements, indicating that qualitative binary data may often be sufficient for the purpose of facies discrimination in many branches of geology and that association analysis is an effective method for this purpose. 相似文献
3.
Descriptive Analysis and Classification of Benthic Communities in Some Mediterranean Coastal Lagoons (Central Italy) 总被引:3,自引:0,他引:3
Abstract. Benthic samples were taken seasonally at 32 stations in five coastal lagoons of Central Italy (Fogliano, Monaci, Caprolace, Fondi, and Lungo) during a two-year period (1982–1984). Composition and distribution of benthic populations in each lagoon as well as seasonal trends of species richness, density, diversity, and redundancy are presented and discussed.
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
4.
红树林遥感智能分类方法研究 总被引:13,自引:0,他引:13
利用GIS信息中的红树林地域分布规律作向导,充分利用械树林区的光谱信息进行红树林植被信息提取。在对比研究常规的红树林图象自理方法的基础上,提出了适用于红树林植被信息遥感监测的智能分类方法。 相似文献
5.
6.
用于数值分类的聚类分析 总被引:24,自引:0,他引:24
这里所谓聚类分析包括传统的聚类分析和作者提出的聚类统计检验分析。传统的聚类分析是常用的重要数值分类方法。但是,这个方法由于缺乏显著性检验,在国际上已长期公认是一个在多元统计中并不完整的方法。本文把聚类统计检验分析在其具有显著性检验的优越性上,和传统聚类分析作了对比分析。聚类统计检验分析区分有均匀聚类与中心聚类。前者用(16)作为聚类判据,后者则用(27),并且各用相应的公式(17)-(21)与(2 相似文献
7.
8.
9.
10.
闫晓光 《测绘与空间地理信息》2008,31(2):67-70
阐述了基于GIS房产管理的关键是建立统一的数据分类与编码标准,核心是建立房屋的空间地理属性信息、自然属性信息、社会人文属性信息的链接,基础是建立房产地理信息数据库。并提出了建立房产地理信息数据库的方法、设计思路和方式。 相似文献