全文获取类型
收费全文 | 56395篇 |
免费 | 10449篇 |
国内免费 | 10251篇 |
专业分类
测绘学 | 4587篇 |
大气科学 | 6873篇 |
地球物理 | 19745篇 |
地质学 | 23938篇 |
海洋学 | 5916篇 |
天文学 | 4354篇 |
综合类 | 4104篇 |
自然地理 | 7578篇 |
出版年
2024年 | 216篇 |
2023年 | 645篇 |
2022年 | 1706篇 |
2021年 | 2141篇 |
2020年 | 2035篇 |
2019年 | 2506篇 |
2018年 | 1932篇 |
2017年 | 2212篇 |
2016年 | 2076篇 |
2015年 | 2484篇 |
2014年 | 3098篇 |
2013年 | 3179篇 |
2012年 | 3274篇 |
2011年 | 3477篇 |
2010年 | 3043篇 |
2009年 | 3882篇 |
2008年 | 3635篇 |
2007年 | 3868篇 |
2006年 | 3701篇 |
2005年 | 3476篇 |
2004年 | 3113篇 |
2003年 | 2917篇 |
2002年 | 2487篇 |
2001年 | 2207篇 |
2000年 | 2222篇 |
1999年 | 1978篇 |
1998年 | 1779篇 |
1997年 | 1415篇 |
1996年 | 1206篇 |
1995年 | 1050篇 |
1994年 | 983篇 |
1993年 | 793篇 |
1992年 | 626篇 |
1991年 | 465篇 |
1990年 | 324篇 |
1989年 | 251篇 |
1988年 | 209篇 |
1987年 | 125篇 |
1986年 | 79篇 |
1985年 | 57篇 |
1984年 | 33篇 |
1983年 | 24篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 27篇 |
1978年 | 24篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1954年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
WANGXie-kang HUANGEr CUIPeng 《中国地理科学(英文版)》2003,13(3):262-266
Debris flow is one of the most destructive phenomena of natural hazards. Recently, major natural haz-ard, claiming human lives and assets, is due to debris flow in the world. Several practical methods for forecasting de-bris flow have been proposed, however, the accuracy of these methods is not high enough for practical use because of the stochastic and non-linear characteristics of debris flow. Artificial neural network has proven to be feasible and use-fill in developing models for nonlinear systems. On the other hand, predicting the future behavior based on a time se-ries of collected historical data is also an important tool in many scientific applications. In this study we present a three-layer feed-forward neural network model to forecast surge of debris flow according to the time series data collect-ed in the Jiangjia Ravine, situated in north part of Yunnan Province of China. The simulation and prediction of debris flow using the proposed approach shows this model is feasible, however, further studies are needed. 相似文献
72.
73.
昆仑山口大地震与地形变异常的讨论 总被引:7,自引:5,他引:2
针对昆仑山口大地震,总结了多种地形变(大地测量)手段所显示的异常变化及其时空分布,结果显示:8.1级大震前存在空间尺度大,时间尺度的地形变前兆异常,简要介绍了相关的异常图像,给出了初步解释,并对未来震情的发展进行了探讨,认为近期内强震活动向华北迁移的可能性不大。 相似文献
74.
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
75.
Larisa A. Yakovina Yakiv V. Pavlenko Carlos Abia 《Astrophysics and Space Science》2003,288(3):279-286
Lithium abundances in the atmospheres of the super Li-rich C-giants WZ Cas and WX Cyg are derived by the spectral synthesis
technique using the Li I resonance line at λ670.8 nm and three subordinate lines at λλ 812.6, 610.4 and 497.2 nm. The differences
between the Li abundances derived from the λ670.8 nm line and the λλ 497.2, 812.6 nm lines do not exceed ±0.5 dex. The lithium
line at λ610.4 nm provides typically lower abundances than the resonance line (by ≈ 1 dex). The mean LTE and NLTE Li abundances
from three Li I lines (excluding λ610.4 nm) are 4.7, 4.9 for WZ Cas, and 4.6, 4.8 for WX Cyg, respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
76.
韩玲 《地球科学与环境学报》2003,25(1):74-75
提出了一种基于格网DEM的粗差检测及剔除方法,其基本思想是对每个表面上的点,在坡度上,高程或突变量引起的形状不连续,可能被怀疑有误差,通过坡度上每个点,应用坡度逼近或改变量来计算,考虑坡度变化的相对值,并以这些相对值计算一个统计值为判断该点合法性的阈值,使计算结果更为可靠。 相似文献
77.
应用GPS观测青藏高原东北缘应力场变化 总被引:2,自引:0,他引:2
采用各向同性弹性地球模型推导了地面位移场速率与地壳内任意点应力场变化的边界积分关系,同时利用青藏高原东北缘1999~2001年观测的GPS资料对观测区地壳深度为5 km和25 km的主应力和最大剪应力进行了计算分析.结果表明,青藏高原东北缘的主应力变化主要集中在祁连山断裂、海原断裂等,在1920~1954年间历史上发生过多次震级为7.0~8.5级强震的断裂附近,并具有主应力变化沿断层走向分布、最大剪应力沿断层走向交替变化等特征. 相似文献
78.
79.
80.
Cristiano B. Cosmovici Vojko Bratina Gottfried Schwarz Gianpaolo Tozzi Michael J. Mumma Roberto Stalio 《Astrophysics and Space Science》2006,301(1-4):135-143
We report here on unique post-perihelion (2.3 AU) measurements of Comet Hale-Bopp in the FUV-range (950–1250 Å) by means of the UVSTAR spectrometer from the space shuttle with the main purpose of searching for argon and other FUV emitters. New methods for separating the strong airglow emission at shuttle altitudes are here discussed in detail. Due to our low resolution (15 Å) and S/N ratio the possible rocket-borne detection of argon near perihelion (0.9 AU) could not be confirmed. New species as N2 are suspected but difficult to separate from the strong airglow emission at shuttle altitudes. From the Lyα brightness (1.30± 0.08 kRy) a water production rate Q = 5.9 ± 0.4 × 1029 molecules s?1 could be derived and compared with other post-perihelion observations. 相似文献