全文获取类型
收费全文 | 36660篇 |
免费 | 4822篇 |
国内免费 | 7119篇 |
专业分类
测绘学 | 3858篇 |
大气科学 | 4647篇 |
地球物理 | 8010篇 |
地质学 | 14641篇 |
海洋学 | 4417篇 |
天文学 | 6240篇 |
综合类 | 2317篇 |
自然地理 | 4471篇 |
出版年
2024年 | 111篇 |
2023年 | 368篇 |
2022年 | 928篇 |
2021年 | 1172篇 |
2020年 | 1319篇 |
2019年 | 1690篇 |
2018年 | 1183篇 |
2017年 | 1444篇 |
2016年 | 1474篇 |
2015年 | 1581篇 |
2014年 | 2128篇 |
2013年 | 2469篇 |
2012年 | 2194篇 |
2011年 | 2474篇 |
2010年 | 2141篇 |
2009年 | 2796篇 |
2008年 | 2711篇 |
2007年 | 2732篇 |
2006年 | 2586篇 |
2005年 | 2138篇 |
2004年 | 1929篇 |
2003年 | 1620篇 |
2002年 | 1266篇 |
2001年 | 1136篇 |
2000年 | 1015篇 |
1999年 | 950篇 |
1998年 | 870篇 |
1997年 | 660篇 |
1996年 | 566篇 |
1995年 | 511篇 |
1994年 | 422篇 |
1993年 | 427篇 |
1992年 | 286篇 |
1991年 | 242篇 |
1990年 | 185篇 |
1989年 | 170篇 |
1988年 | 141篇 |
1987年 | 70篇 |
1986年 | 79篇 |
1985年 | 78篇 |
1984年 | 50篇 |
1983年 | 28篇 |
1982年 | 40篇 |
1981年 | 27篇 |
1980年 | 33篇 |
1979年 | 15篇 |
1978年 | 20篇 |
1977年 | 35篇 |
1976年 | 25篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
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
132.
寇新建 《大地测量与地球动力学》1994,(3)
由于观测条件的变化,观测值方差将产生随机波动。本文根据Bayes估计理论,推导了线性模型待估参数的分布函数及观测值方差估计公式,并将其用于位移检验。计算结果表明,在同样的置信度下,本方法更符合实际。文中还对参数估值的统计性质进行了讨论。 相似文献
133.
134.
135.
136.
137.
138.
M. R. Bate S. H. Lubow G. I. Ogilvie K. A. Miller 《Monthly notices of the Royal Astronomical Society》2003,341(1):213-229
We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M⊕ ) to 1 Jupiter mass (1 MJ ) by using the zeus hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses M p ≳ 0.1 MJ produce significant perturbations in the surface density of the disc. The flow within the Roche lobe of the planet is fully three-dimensional. Gas streams generally enter the Roche lobe close to the disc mid-plane, but produce much weaker shocks than the streams in two-dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the orbit of the planet. Much of the mass supply to the circumplanetary disc comes from non-coplanar flow. The accretion rate peaks with a planet mass of approximately 0.1 MJ and is highly efficient, occurring at the local viscous rate. The migration time-scales for planets of mass less than 0.1 MJ , based on torques from disc material outside the Roche lobes of the planets, are in excellent agreement with the linear theory of type I (non-gap) migration for three-dimensional discs. The transition from type I to type II (gap) migration is smooth, with changes in migration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few MJ with little migration. Planets with final masses of the order of 10 MJ would undergo large migration, which makes formation and survival difficult. 相似文献
139.
140.