全文获取类型
收费全文 | 4821篇 |
免费 | 977篇 |
国内免费 | 1372篇 |
专业分类
测绘学 | 112篇 |
大气科学 | 2031篇 |
地球物理 | 1226篇 |
地质学 | 944篇 |
海洋学 | 1155篇 |
天文学 | 911篇 |
综合类 | 152篇 |
自然地理 | 639篇 |
出版年
2024年 | 24篇 |
2023年 | 92篇 |
2022年 | 149篇 |
2021年 | 172篇 |
2020年 | 202篇 |
2019年 | 284篇 |
2018年 | 198篇 |
2017年 | 232篇 |
2016年 | 204篇 |
2015年 | 220篇 |
2014年 | 289篇 |
2013年 | 325篇 |
2012年 | 295篇 |
2011年 | 316篇 |
2010年 | 255篇 |
2009年 | 404篇 |
2008年 | 366篇 |
2007年 | 395篇 |
2006年 | 335篇 |
2005年 | 279篇 |
2004年 | 262篇 |
2003年 | 233篇 |
2002年 | 205篇 |
2001年 | 151篇 |
2000年 | 184篇 |
1999年 | 146篇 |
1998年 | 141篇 |
1997年 | 106篇 |
1996年 | 147篇 |
1995年 | 102篇 |
1994年 | 89篇 |
1993年 | 90篇 |
1992年 | 64篇 |
1991年 | 48篇 |
1990年 | 35篇 |
1989年 | 27篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 10篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有7170条查询结果,搜索用时 15 毫秒
1.
A highly automated moving object detection package 总被引:1,自引:0,他引:1
2.
S.J Weidenschilling 《Icarus》2003,165(2):438-442
For standard cosmic abundances of heavy elements, a layer of small particles in the central plane of the solar nebula cannot attain the critical density for gravitational instability. Youdin and Shu (2002, Astrophys. J. 580, 494-505) suggest that the local surface density of solids can be enhanced by radial migration of particles due to gas drag. However, they consider only motions of individual particles. Collective motion due to turbulent stress on the particle layer acts to inhibit such enhancement and may prevent gravitational instability. 相似文献
3.
In the frame of 2D-static problems one approaches the problem of elastic-NRT (not-resisting tension) semi-plane loaded on its limit line. This problem is intended to model the stress situation induced in the soil by a foundation structure. The solution, in terms of activated stress field, is searched for in the class of stress fields satisfying equilibrium and admissibility conditions, by applying an energy approach. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
4.
Anita Enmark Thomas Berkefeld Oskar von der Lühe Torben Andersen 《Experimental Astronomy》2006,21(2):87-99
A simulation model of the adaptive optics of the German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife, is
presented. The model uses modules from the integrated model of the Euro50 extremely large telescope, and includes submodels
of a Shack-Hartmann wavefront sensor, a de-formable mirror, a tip-tilt mirror, high-voltage amplifier low-pass filters, a
reconstructor and a controller. We investigate the impact on the closed loop bandwidth of changes in controller configuration
and certain system parameters, such as low pass filter bandwidth and camera integration and readout time. Control strategies
were tested on simple models before implementation on the full VTT model. Using the models, different control strategies are
compared. 相似文献
5.
6.
We examine possible locations for the primordial disk of the Edgeworth-Kuiper Belt (EKB), using several subsets of the known objects as markers of the total mass distribution. Using a secular perturbation theory, we find that the primordial plane of the EKB could have remained thin enough to escape detection only if it is clustered very closely about the invariable plane of the Solar System. 相似文献
7.
介绍了太阳22周峰年期间云南天文台米波射电频谱仪的观测结果。主要对1557个单个Spike的时间和频率分布作了统计分析,着重指出太阳快速精细结构的观测特征并定性地指出其产生机制。 相似文献
8.
M. L. Demidov 《Solar physics》1996,164(1-2):381-388
The zero level problem of solar magnetographs is particularly important for observations of large-scale magnetic fields on the Sun. Experiments conducted at the STOP telescope of the Sayan observatory show that, in addition to adjustment errors of the polarization analyzer and the spectrograph focusing, spurious signals of the magnetograph are caused by polarization effects in optical components preceding the polarization analyzer and aberration errors of the spectrograph. 相似文献
9.
T. Masuda T. Shibutani T. Ochiai S. Akagi H. Yamaguchi Y. Kugimiya N. Kimura T. Miyake 《Journal of Metamorphic Geology》2004,22(3):199-205
Evidence is presented of a lateral variation in differential stress during metamorphism along a regional metamorphic belt on the basis of the proportion of microboudinaged piemontite grains (p) in a quartz matrix in metacherts. It is proposed that p is a practical indicator of relative differential stress. Analysis of 123 metacherts from the 800 km long Sambagawa metamorphic belt, Japan, reveals that p‐values range from < 0.01 to 0.7 in this region. Most samples from Wakayama in the mid‐belt area have p‐values of 0.4–0.6, whereas those from western Shikoku have p‐values of < 0.1. This difference cannot be explained by variations in metamorphic temperature, and is instead attributed to a regional, lateral variation in differential stress during metamorphism. 相似文献
10.
Astronomy Letters - The acceleration of anomalous cosmic rays (ACRs) at the heliospheric termination shock and their influence on the shock structure and location are analyzed in terms of a... 相似文献