全文获取类型
收费全文 | 50279篇 |
免费 | 9395篇 |
国内免费 | 12357篇 |
专业分类
测绘学 | 3280篇 |
大气科学 | 10344篇 |
地球物理 | 12830篇 |
地质学 | 25369篇 |
海洋学 | 6287篇 |
天文学 | 2328篇 |
综合类 | 5507篇 |
自然地理 | 6086篇 |
出版年
2024年 | 157篇 |
2023年 | 713篇 |
2022年 | 2076篇 |
2021年 | 2354篇 |
2020年 | 1994篇 |
2019年 | 2300篇 |
2018年 | 2706篇 |
2017年 | 2511篇 |
2016年 | 2901篇 |
2015年 | 2411篇 |
2014年 | 2897篇 |
2013年 | 3032篇 |
2012年 | 2892篇 |
2011年 | 2992篇 |
2010年 | 3047篇 |
2009年 | 2967篇 |
2008年 | 2815篇 |
2007年 | 2614篇 |
2006年 | 2187篇 |
2005年 | 2046篇 |
2004年 | 1586篇 |
2003年 | 1577篇 |
2002年 | 1540篇 |
2001年 | 1480篇 |
2000年 | 1753篇 |
1999年 | 2404篇 |
1998年 | 1901篇 |
1997年 | 1948篇 |
1996年 | 1777篇 |
1995年 | 1529篇 |
1994年 | 1366篇 |
1993年 | 1163篇 |
1992年 | 901篇 |
1991年 | 706篇 |
1990年 | 548篇 |
1989年 | 463篇 |
1988年 | 441篇 |
1987年 | 285篇 |
1986年 | 237篇 |
1985年 | 171篇 |
1984年 | 109篇 |
1983年 | 93篇 |
1982年 | 96篇 |
1981年 | 77篇 |
1980年 | 61篇 |
1979年 | 56篇 |
1978年 | 25篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1958年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
We describe how a local plasma structure can be changed by a transverse shear flow using numerical simulation to investigate the disturbance process near the magnetopause. The results show that magnetic field lines are bent by transverse shear flow disturbance near the current sheet region. There are multiple bipolar structures of the normal magnetic field in the numerical simulation. We term this new feature as K-point magnetic reconnection, realistic for discussing space observations. 相似文献
152.
Qing-Yao Liu Yu-Lan Yang National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 《中国天文和天体物理学报》2006,6(3):331-337
The variation in the orbital period of the W UMa type contact binary V502 Oph is analyzed. The orbital period exhibits a wavelike variation with a periodicity of 23.0 years and an amplitude of △P = 1.24×10~(-6) days superimposed on secular decrease of dP/dt = 1.68×10-7 day per year. The long-term decrease may be accompanied by the contraction of the secondary at a rate of 83 m per year and a mass transfer rate from the primary to the secondary of 4.28×10~8 M per year. The short-term oscillation may be explained by the presence of a third component. Orbital elements of the third body and its possible mass are presented. 相似文献
153.
On September 14–18, 2000, a medium-small solar active region was observed at Ganyu Station of Purple Mountain Observatory. Its spots were not large, but it had a peculiar active filament. On Sep.16, a flare of importance IIIb with rather intense geophysical effects was produced. Our computation of the magnetic structure of the active region reveals that the rope-shaped filament was concerned with a low magnetic arc close to magnetic neutral line. An intense shear of magnetic field occurred near magnetic rope. The QSL analysis shows that a 3-D magnetic reconnection might appear in the vicinity of filament, and this can be used to interpret the formation of a large flare. 相似文献
154.
1INTRODUCTION Since the first use in human genetic research in1966,allozyme has become the most popular genetic marker for population genetics studies for almost all groups of animals and plants(Lewontin and Hubby,1966;Murphy et al.,1996).In the past seve… 相似文献
155.
Z. Q. Qu C. L. Xu X. Y. Zhang X. L. Yan C. L. Jin 《Monthly notices of the Royal Astronomical Society》2006,370(4):1790-1796
The influence of magnetic fields on the energy level populations of atoms is firstly studied by analysing the Stokes profiles of Fe i 6302.5 forming in the solar magnetized atmosphere, with the aid of a departure factor defined to evaluate the deviation from the normal Boltzmann distribution without a magnetic field. This factor is directly related to the ratio of line-source function to the continuum one. The relationship between the departure and the magnetic field reveals an effect that the magnetic field induces an exponential increase in the level population of the lower level of Fe i 6302.5 (Landé factor g = 2.5 ) with the field strength. This indicates that the magnetic field can cause the redistribution of populations of those levels whose Landé factors are non-zero. Therefore, this effect should be included in the calculation of the statistical equilibrium. Secondly, an experiment utilizing the Hg5461 line in the laboratory on the Earth is carried out to reveal that the exponential relation is independent of variations in temperature, and the excitation is completely magneto-induced. Finally, the exponential relation is explained by taking account of the magnetic energy in the Boltzmann distribution. 相似文献
156.
For a Hamiltonian that can be separated into N+1(N\geq 2) integrable parts, four algorithms can be built for a symplectic integrator. This research compares these algorithms for the
first and second order integrators. We found that they have similar local truncation errors represented by error Hamiltonian
but rather different numerical stability. When the computation of the main part of the Hamiltonian, H
0, is not expensive, we recommend to use S
* type algorithm, which cuts the calculation of the H
0 system into several small time steps as Malhotra(1991) did. As to the order of the N+1 parts in one step calculation, we found that from the large to small would get a slower error accumulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
157.
158.
159.
张众服 《大地测量与地球动力学》1996,(4)
利用三峡地区多年的地形变观测资料,分析了该区的地形变特征。结果表明,各断层活动性甚微或基本不活动,区域地壳相对稳定 相似文献
160.
黑色高岭石粘土岩,是铜川王石凹煤矿石炭纪煤系地层顶部,五号煤层的上部一层稳定的煤矸石。经偏光显微镜及费氏台测试光性特征、化学试验及分析鉴定表明,这是一种由高岭石组成的,成分很纯、颗粒大、结晶良好的高岭石粘土岩。据微量元素含量分析,此高岭石系淡水沉积物。 相似文献