全文获取类型
收费全文 | 30796篇 |
免费 | 556篇 |
国内免费 | 821篇 |
专业分类
测绘学 | 961篇 |
大气科学 | 2751篇 |
地球物理 | 5262篇 |
地质学 | 14639篇 |
海洋学 | 2095篇 |
天文学 | 4929篇 |
综合类 | 435篇 |
自然地理 | 1101篇 |
出版年
2023年 | 43篇 |
2022年 | 132篇 |
2021年 | 142篇 |
2020年 | 126篇 |
2019年 | 141篇 |
2018年 | 3479篇 |
2017年 | 3310篇 |
2016年 | 1982篇 |
2015年 | 312篇 |
2014年 | 329篇 |
2013年 | 345篇 |
2012年 | 1464篇 |
2011年 | 3273篇 |
2010年 | 3044篇 |
2009年 | 3131篇 |
2008年 | 2450篇 |
2007年 | 3167篇 |
2006年 | 368篇 |
2005年 | 736篇 |
2004年 | 584篇 |
2003年 | 665篇 |
2002年 | 438篇 |
2001年 | 170篇 |
2000年 | 203篇 |
1999年 | 177篇 |
1998年 | 191篇 |
1997年 | 192篇 |
1996年 | 170篇 |
1995年 | 117篇 |
1994年 | 102篇 |
1993年 | 132篇 |
1992年 | 74篇 |
1991年 | 83篇 |
1990年 | 53篇 |
1989年 | 59篇 |
1988年 | 63篇 |
1987年 | 61篇 |
1986年 | 65篇 |
1985年 | 50篇 |
1984年 | 57篇 |
1983年 | 51篇 |
1982年 | 53篇 |
1981年 | 55篇 |
1980年 | 55篇 |
1979年 | 36篇 |
1977年 | 21篇 |
1976年 | 27篇 |
1975年 | 23篇 |
1974年 | 20篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 984 毫秒
1.
The geodynamic mechanism of the late Early Cretaceous magmatic flare‐up in the collisional zone between the Lhasa and Qiangtang terranes in Tibet is controversial because of a scarcity of robust evidence. To address this problem, we report geochronological, geochemical and Hf isotopic data for the newly discovered Gufeng gabbros from the Duolong Cu–Au mineral district of the western Bangong–Nujiang Suture Zone (BNSZ). The gabbro samples, dated at 126.3 ± 1.8 Ma, show geochemical similarities to typical ocean island basalt (OIB) and have positive εHf(t) values of +3.3 to +6.9. The gabbros were generated by decompression melting of deep upwelling asthenosphere. This event is best explained by slab break‐off and the resultant development of a slab window beneath central Tibet. 相似文献
2.
3.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
4.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
5.
6.
本文依据稳恒磁场中的高斯定理和安培环路定理,用迭代法推导出对称轴上的磁感应强度与空间任意一点磁感应强度的关系式,从而可得出轴对称稳恒磁场的无电流分布空间的解式。 相似文献
7.
本文针对低纬度地区频率域化磁极存在的问题,在频谱分析的基础上,提出了一种新的滤波方法即振幅滤波法。该方法能将低纬度地区化极磁场的频谱恢复到垂直磁化磁场的频谱,大大提高了低纬度地区化磁极的精度。 相似文献
8.
A spectacular change in the lower corona on the south-west limb has been found in solar images taken by the Yohkoh soft X-ray telescope. The event is characterized by a large topological change in magnetic field and a large intensity decrease observed after the X1. 1/1B flare on 9 November, 1991. A coronal mass ejection (CME) was observed by the Mark III K-coronameter (MK3) at the HAO/Mauna Loa Observatory. Both the MK3 (white-light) and soft X-ray observations showed that one leg of this CME was located above the flare site. An interplanetary shock associated with this event was observed by Pioneer Venus Orbiter, and, possibly, by IMP-8.Also Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309, U.S.A. 相似文献
9.
10.
B. A. Ivanov 《Solar System Research》2005,39(5):381-409
Multi-ring impact basins have been found on the surfaces of almost all planetary bodies in the Solar system with solid crusts. The details of their formation mechanism are still unclear. We present results of our numerical modeling of the formation of the largest known terrestrial impact craters. The geological and geophysical data on these structures accumulated over many decades are used to place constraints on the parameters of available numerical models with a dual purpose: (i) to choose parameters in available mechanical models for the crustal response of planetary bodies to a large impact and (ii) to use numerical modeling to refine the possible range of original diameters and the morphology of partially eroded terrestrial craters. We present numerical modeling results for the Vredefort, Sudbury, Chicxulub, and Popigai impact craters and compare these results with available geological and geophysical information. 相似文献