全文获取类型
收费全文 | 54000篇 |
免费 | 10085篇 |
国内免费 | 13887篇 |
专业分类
测绘学 | 5158篇 |
大气科学 | 10795篇 |
地球物理 | 12498篇 |
地质学 | 27423篇 |
海洋学 | 7441篇 |
天文学 | 2085篇 |
综合类 | 5533篇 |
自然地理 | 7039篇 |
出版年
2024年 | 193篇 |
2023年 | 759篇 |
2022年 | 2403篇 |
2021年 | 2822篇 |
2020年 | 2336篇 |
2019年 | 2674篇 |
2018年 | 2944篇 |
2017年 | 2793篇 |
2016年 | 3123篇 |
2015年 | 2865篇 |
2014年 | 3278篇 |
2013年 | 3427篇 |
2012年 | 3493篇 |
2011年 | 3618篇 |
2010年 | 3658篇 |
2009年 | 3346篇 |
2008年 | 3187篇 |
2007年 | 2929篇 |
2006年 | 2487篇 |
2005年 | 2225篇 |
2004年 | 1743篇 |
2003年 | 1665篇 |
2002年 | 1710篇 |
2001年 | 1724篇 |
2000年 | 1751篇 |
1999年 | 2215篇 |
1998年 | 1712篇 |
1997年 | 1650篇 |
1996年 | 1484篇 |
1995年 | 1342篇 |
1994年 | 1185篇 |
1993年 | 1111篇 |
1992年 | 846篇 |
1991年 | 686篇 |
1990年 | 492篇 |
1989年 | 458篇 |
1988年 | 402篇 |
1987年 | 250篇 |
1986年 | 201篇 |
1985年 | 139篇 |
1984年 | 126篇 |
1983年 | 96篇 |
1982年 | 111篇 |
1981年 | 78篇 |
1980年 | 53篇 |
1979年 | 47篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 15篇 |
1958年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The effect of ocean wave breaking as a non-Bragg mechanism on backscattering cross-section and modulation transfer functions (MTF) of radar was investigated based on Bragg resonance theory and parametric method. The result showed that the additional effect of wave breaking on backscattering cross-section is not more than 20% except for the small incident angle of VV polarized electromagnetic (e.m.) wave but is significant for HH polarized e.m. wave. Breaking waves lead to increase in the modulus of tilt modulation MTF and the larger the wind speed, the faster the increase. For large incident angle, the modulus of tilt modulation MTF with wave breaking decreases quickly with incident angle for HH polarization and approach to that without wave breaking for VV polarization. The hydrodynamic MTF increases 30%-60% when considering wave breaking and the increase is larger for HH polarization than for VV polarization. 相似文献
102.
103.
This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
104.
The dunes in estuary of Tumen River in China lie to the area between the Jiushaping and Fangchuan in the left bank of Tumen River (Fig.1). The dis-tance is about 15~20 km between the dunes and the coast. It ranges from China to D. P. R. Korea and Russia. The range of the height of dunes is about 15~20 m and the width is 100~200 m. By the re-connaissance, we protracted 9 section planes of the dunes and collected 40 sand samples of the dunes, and identified the sedimentary environment … 相似文献
105.
Hong-Qi Zhang Xing-Ming Bao Yin Zhang Ji-Hong Liu Shu-Dong Bao Yuan-Yong Deng Wei Li Jie Chen Jin-Ping Dun Jiang-Tao Su Juan Guo Xiao-Fan Wang Ke-Liang Hu Gang-Hua Lin Dong-Guang WangNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):491-494
We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle. 相似文献
106.
本文讨论了彗星中尘埃粒子的充电机制 ,带电特性和平衡电势的变化规律 ,分析了彗星尘埃的破碎特性和临界半径 ,得出了很有意义的结果 相似文献
107.
108.
Pco2 of air and seawater samples from the East China Sea(ECS) were measured in situ in autumn, 1994,Ocean currents,terrestrial fluviation,biological activities,etc.,Pco2 char-acters in air and seawater were investigated,CO2 flux and its character in the East China Sea are discussed on the basis of the Pco2 profiles of air and seawater,It was clear that the nearshore was the source of CO2;and tht the oulter sea area was the sink of CO2; and that the shelf area of the EXS is a net sink for atmospheric CO2 in autumn. 相似文献
109.
刘峰 《成都信息工程学院学报》2003,18(4):376-380
分组密码是数据通讯中最常用的数据加密方式,以DES为例分析现有分组加密算法的安全隐患,并提出了可变密钥加密和变长密文输出两个新思路,可应用于所有现有分组加密算法以提高安全性,并就该方法的安全性、效率、具体应用做出了分析。 相似文献
110.