全文获取类型
收费全文 | 25470篇 |
免费 | 3685篇 |
国内免费 | 5224篇 |
专业分类
测绘学 | 3321篇 |
大气科学 | 3975篇 |
地球物理 | 6345篇 |
地质学 | 10724篇 |
海洋学 | 3243篇 |
天文学 | 1093篇 |
综合类 | 1779篇 |
自然地理 | 3899篇 |
出版年
2024年 | 129篇 |
2023年 | 406篇 |
2022年 | 757篇 |
2021年 | 974篇 |
2020年 | 1117篇 |
2019年 | 1334篇 |
2018年 | 930篇 |
2017年 | 1236篇 |
2016年 | 1250篇 |
2015年 | 1288篇 |
2014年 | 1616篇 |
2013年 | 1901篇 |
2012年 | 1588篇 |
2011年 | 1676篇 |
2010年 | 1329篇 |
2009年 | 1712篇 |
2008年 | 1684篇 |
2007年 | 1731篇 |
2006年 | 1677篇 |
2005年 | 1315篇 |
2004年 | 1229篇 |
2003年 | 1040篇 |
2002年 | 810篇 |
2001年 | 714篇 |
2000年 | 640篇 |
1999年 | 597篇 |
1998年 | 602篇 |
1997年 | 519篇 |
1996年 | 426篇 |
1995年 | 380篇 |
1994年 | 315篇 |
1993年 | 312篇 |
1992年 | 215篇 |
1991年 | 172篇 |
1990年 | 133篇 |
1989年 | 127篇 |
1988年 | 104篇 |
1987年 | 59篇 |
1986年 | 53篇 |
1985年 | 52篇 |
1984年 | 29篇 |
1983年 | 13篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1978年 | 13篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
WEIHai-quan JINBo-lu LIUYong-shun 《东北亚地学研究》2004,7(1):28-35
A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temporamre feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption. 相似文献
43.
The UV spectra of mixture solutions consisting of tyrosine,tryptophane,phenylalanine,cystine,histidineand 3,4-dihydroxyl phenylalanine have been measured.The numbers,identities and concentrations of theamino acids in the mixtures have been determined successfully using target factor analysis.The effectsof the wavelength range and the selected sampling interval on the results are discussed.Twenty-fivesynthetic mixture samples have been analysed successfully.The average recoveries are 98·9 for Tyr,96·5for Trp,105·6 for Phe,98·1 for Cys,98·9 for His and 106·4 for Di-phe.The results obtained are ingood agreement with those obtained by the Kalman filter method. 相似文献
44.
45.
46.
Jacques Laskar 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):191-196
Frequency analysis is a new method for analyzing the stability of orbits in a conservative dynamical system. It was first devised in order to study the stability of the solar system (Laskar, Icarus, 88, 1990). It is a powerful method for analyzing weakly chaotic motion in hamiltonian systems or symplectic maps. For regular motions, it yields an analytical representation of the solutions. In cases of 2 degrees of freedom system with monotonous torsion, precise numerical criterions for the destruction of KAM tori can be found. For a 4D symplectic map, plotting the frequency map in the frequency plane provides a clear representation of the global dynamics and describes the actual Arnold web of the system. 相似文献
47.
48.
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
49.
张晓晖 《成都信息工程学院学报》2002,17(3):166-169
通过对影响能见度的因素的分析,提出了一种能见度预报方法-综合分析法,极大地提高了能见度的预报准确率。 相似文献
50.
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