全文获取类型
收费全文 | 25145篇 |
免费 | 4381篇 |
国内免费 | 3438篇 |
专业分类
测绘学 | 5442篇 |
大气科学 | 2124篇 |
地球物理 | 9584篇 |
地质学 | 8115篇 |
海洋学 | 2109篇 |
天文学 | 1255篇 |
综合类 | 1976篇 |
自然地理 | 2359篇 |
出版年
2024年 | 165篇 |
2023年 | 401篇 |
2022年 | 883篇 |
2021年 | 1138篇 |
2020年 | 1181篇 |
2019年 | 1277篇 |
2018年 | 914篇 |
2017年 | 1176篇 |
2016年 | 1093篇 |
2015年 | 1200篇 |
2014年 | 1394篇 |
2013年 | 1619篇 |
2012年 | 1531篇 |
2011年 | 1524篇 |
2010年 | 1212篇 |
2009年 | 1496篇 |
2008年 | 1433篇 |
2007年 | 1718篇 |
2006年 | 1655篇 |
2005年 | 1350篇 |
2004年 | 1323篇 |
2003年 | 1089篇 |
2002年 | 921篇 |
2001年 | 721篇 |
2000年 | 690篇 |
1999年 | 600篇 |
1998年 | 524篇 |
1997年 | 426篇 |
1996年 | 451篇 |
1995年 | 383篇 |
1994年 | 333篇 |
1993年 | 299篇 |
1992年 | 198篇 |
1991年 | 140篇 |
1990年 | 101篇 |
1989年 | 102篇 |
1988年 | 78篇 |
1987年 | 58篇 |
1986年 | 43篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 20篇 |
1977年 | 11篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
7.
We present the excitation energies and lifetimes for the 3 s 3 p 3 d 4 F 7/2,9/2 levels for five aluminium-like ions of the iron group. Apart from the wavelengths, this also includes the transition probabilities and branching ratios for the electric-dipole allowed (E1) and forbidden (M1, E2, M2) lines into the energetically lower lying levels of the 3 s 2 3 d , 3 s 3 p 2 and 3 s 3 p 3 d configurations. Applying systematically enlarged multiconfiguration Dirac–Fock (MCDF) wavefunctions, here the effects of relativity and the electron–electron correlation are treated within the same (computational) model. 相似文献
8.
Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination. 相似文献
9.
In urban environments, one major concern with deep excavations in soft clay is the potentially large ground deformations in and around the excavation. Excessive movements can damage adjacent buildings and utilities. There are many uncertainties associated with the calculation of the ultimate or serviceability performance of a braced excavation system. These include the variabilities of the loadings, geotechnical soil properties, and engineering and geometrical properties of the wall. A risk‐based approach to serviceability performance failure is necessary to incorporate systematically the uncertainties associated with the various design parameters. This paper demonstrates the use of an integrated neural network–reliability method to assess the risk of serviceability failure through the calculation of the reliability index. By first performing a series of parametric studies using the finite element method and then approximating the non‐linear limit state surface (the boundary separating the safe and ‘failure’ domains) through a neural network model, the reliability index can be determined with the aid of a spreadsheet. Two illustrative examples are presented to show how the serviceability performance for braced excavation problems can be assessed using the reliability index. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
10.
Temperature data from 18 measurement series obtained during logging of the Oseberg field in the northern North Sea are presented. Because the measurement series are taken at approximately the same depth, they should give identical temperatures after depth correction, and are suitable for assessing the performance of different models used to determine virgin rock temperatures from well log information.We have used this data set to test the properties of the different models given by Shen and Beck (1986). Although these models were built to simulate closely the thermal recovery of a well and are unbiased, the uncertainties in the temperature estimates when applied to real data are found to be no less than those from simpler (biased) models. This fact confirms the conclusion of Hermanrud (1989a) who showed that physical factors other than those presently accounted for significantly influence the thermal recovery of a borehole. 相似文献