全文获取类型
收费全文 | 16504篇 |
免费 | 1841篇 |
国内免费 | 2139篇 |
专业分类
测绘学 | 5961篇 |
大气科学 | 2238篇 |
地球物理 | 2295篇 |
地质学 | 3868篇 |
海洋学 | 1380篇 |
天文学 | 1252篇 |
综合类 | 1637篇 |
自然地理 | 1853篇 |
出版年
2024年 | 72篇 |
2023年 | 182篇 |
2022年 | 542篇 |
2021年 | 691篇 |
2020年 | 730篇 |
2019年 | 659篇 |
2018年 | 561篇 |
2017年 | 890篇 |
2016年 | 798篇 |
2015年 | 820篇 |
2014年 | 915篇 |
2013年 | 1179篇 |
2012年 | 1026篇 |
2011年 | 973篇 |
2010年 | 742篇 |
2009年 | 934篇 |
2008年 | 976篇 |
2007年 | 1154篇 |
2006年 | 1051篇 |
2005年 | 844篇 |
2004年 | 799篇 |
2003年 | 621篇 |
2002年 | 534篇 |
2001年 | 450篇 |
2000年 | 378篇 |
1999年 | 335篇 |
1998年 | 277篇 |
1997年 | 203篇 |
1996年 | 193篇 |
1995年 | 172篇 |
1994年 | 163篇 |
1993年 | 143篇 |
1992年 | 92篇 |
1991年 | 74篇 |
1990年 | 54篇 |
1989年 | 54篇 |
1988年 | 38篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1973年 | 10篇 |
1972年 | 5篇 |
1971年 | 7篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 370 毫秒
41.
42.
青藏块体东北缘地壳水平运动状态 总被引:10,自引:6,他引:4
应用青藏块体东北缘1999~2003年多期GPS观测资料,计算了不同时段GPS点水平运动速率。通过分析发现:甘青块体可分为东部块体和西部块体,东、西部块体的运动状态存在明显的差异;受2001年11月14日昆仑Ms8.1地震的影响,震后地壳运动状态发生了明显的改变。 相似文献
43.
44.
L. K. Erastova 《Astrophysics》2004,47(4):547-554
Some features of a sample of galaxies from the Second Byurakan Survey are discussed. Most of them are small galaxies with star formation. It is shown that different types of galaxies are in the Survey, with high, medium, and low levels of excitation and continua ranging from blue to relatively red. Many of the galaxies have absorption lines in their spectra; their continua are formed by stars in later spectral classes. 相似文献
45.
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
46.
案例推理的地学应用背景和方法 总被引:3,自引:1,他引:2
案例推理 (CBR)研究 ,是人类认知的一种合理性模型 ,接近于人类认识、解决问题最原始的思维方式 ,具有在无法获取机理模型、确定规则或统计模型时 ,采用简单的历史相似性推理实现问题的定量求解和预测 ,成为人工智能领域近年来的研究热点。 相似文献
47.
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
48.
49.
50.