全文获取类型
收费全文 | 20420篇 |
免费 | 3923篇 |
国内免费 | 5455篇 |
专业分类
测绘学 | 1972篇 |
大气科学 | 4325篇 |
地球物理 | 5086篇 |
地质学 | 10455篇 |
海洋学 | 2765篇 |
天文学 | 887篇 |
综合类 | 1977篇 |
自然地理 | 2331篇 |
出版年
2024年 | 97篇 |
2023年 | 299篇 |
2022年 | 857篇 |
2021年 | 1086篇 |
2020年 | 831篇 |
2019年 | 1027篇 |
2018年 | 1060篇 |
2017年 | 977篇 |
2016年 | 1206篇 |
2015年 | 1019篇 |
2014年 | 1261篇 |
2013年 | 1228篇 |
2012年 | 1173篇 |
2011年 | 1254篇 |
2010年 | 1246篇 |
2009年 | 1226篇 |
2008年 | 1147篇 |
2007年 | 1063篇 |
2006年 | 917篇 |
2005年 | 834篇 |
2004年 | 616篇 |
2003年 | 604篇 |
2002年 | 663篇 |
2001年 | 652篇 |
2000年 | 654篇 |
1999年 | 930篇 |
1998年 | 828篇 |
1997年 | 791篇 |
1996年 | 688篇 |
1995年 | 563篇 |
1994年 | 545篇 |
1993年 | 476篇 |
1992年 | 406篇 |
1991年 | 335篇 |
1990年 | 243篇 |
1989年 | 213篇 |
1988年 | 203篇 |
1987年 | 104篇 |
1986年 | 112篇 |
1985年 | 71篇 |
1984年 | 71篇 |
1983年 | 39篇 |
1982年 | 57篇 |
1981年 | 23篇 |
1980年 | 27篇 |
1979年 | 22篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1962年 | 5篇 |
1958年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Zhi Xu Cheng Fang Wei-Qun Can Astronomy Department of Nanjing University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2005,5(5):519-530
Chromospheric lines, including Ha, Lyα, Lyβand CaⅡK, CaⅡ8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyαline calculation and a smaller intensity enhancement in the Ha line-centers is found than in the previous results of Fang et al. 相似文献
12.
13.
We use the following numerical model for the collapse stage of a Type II supernova of 15 M⊙. Our electron capture rate includes the effects of the inverse reaction and the neutron-proton mass difference. This decreases the electron density at the collapse stage and led to rather large values of the maximum inward velocity and of the corresponding mass (Umax = 3.06 × 109cm/s, Mmax=0.76 M⊙). These larger values are more favourable for the propagation of shock after the rebounce and the triggering-off of a Type-II supernova explosion. For neutrino transport, we use a leakage model and an equilibrium diffusion model, respectively, for the thin and thick stages and a grey atmosphere model to assess the effect of neutrino precipitation on the collapse. We found this effect to be small, the energy precipitation to be not more than 10?5 the neutrino energy loss and the momentum precipitation not more than 10?6 the gravitational acceleration. 相似文献
14.
15.
Xie Rui-xiang Wang Min Shi Shuo-biao Xu Chun Li Wei-hua Yan Yi-hua 《Chinese Astronomy and Astrophysics》2003,27(4):426-434
Using the decimetric (700–1500 MHz) radio spectrometer and the synchronous observational system with high temporal resolution at four frequencies (1420, 2130, 2840 and 4260 MHz) of Yunnan Observatory, two rare events were observed on 2001 June 24 and 1990 July 30. The former was a small radio burst exhibiting pulsations with short periods (about 29, 40 and 100 ms) in the impulsive phase. The latter was a large radio burst, which at 2840 MHz produced radio pulsations with period of about 30 ms. This paper focuses on pulsations with very short periods in the range of 29–40 ms. The mechanism of generation of such pulsations may be modulation of radio radiation by the periodic trains of whistler packets originating in unstable regions of the corona. Alternatively, these pulsations can be attributed to wave-wave non-linear interactions of electrostatic upper hybrid waves driven by beams of precipitating electrons in flaring loops. 相似文献
16.
Wavelet Analysis of Space Solar Telescope Images 总被引:1,自引:0,他引:1
Xi-An Zhu Sheng-Zhen Jin Jing-Yu Wang Shu-Nian NingNational Astronomical Observatories Chinese Academy of Science Beijing Department of Mechanical Electric Engineering China College of Mining Technology Beijing 《中国天文和天体物理学报》2003,3(6):587-596
The scientific satellite SST (Space Solar Telescope) is an important research project strongly supported by the Chinese Academy of Sciences. Every day, SST acquires 50 GB of data (after processing) but only 10GB can be transmitted to the ground because of limited time of satellite passage and limited channel volume. Therefore, the data must be compressed before transmission. Wavelets analysis is a new technique developed over the last 10 years, with great potential of application. We start with a brief introduction to the essential principles of wavelet analysis, and then describe the main idea of embedded zerotree wavelet coding, used for compressing the SST images. The results show that this coding is adequate for the job. 相似文献
17.
Approach to Mountain Hazards in Tibet, China 总被引:1,自引:1,他引:0
MADongtao TUJianjun CUIPeng LURuren 《山地科学学报》2004,1(2):143-154
Tibet is located at the southwest boundary of China. It is the main body of the Qinghai-Tibet Plateau, the highest and the youngest plateau in the world. Owing to complicated geology, Neo-tectonic movements, geomorphology, climate and plateau environment, various mountain hazards, such as debris flow, flash flood, landslide, collapse, snow avalanche and snow drifts, are widely distributed along the Jinsha River (the upper reaches of the Yangtze River), the Nu River and the Lancang River in the east, and the Yarlungzangbo River, the Pumqu River and the Poiqu River in the south and southeast of Tibet. The distribution area of mountain hazards in Tibet is about 589,000 km^2, 49.3% of its total territory. In comparison to other mountain regions in China, mountain hazards in Tibet break out unexpectedly with tremendously large scale and endanger the traffic lines, cities and towns, farmland, grassland, mountain environment, and make more dangers to the neighboring countries, such as Nepal, India, Myanmar and Bhutan. To mitigate mountain hazards, some suggestions are proposed in this paper, such as strengthening scientific research, enhancing joint studies, hazards mitigation planning, hazards warning and forecasting, controlling the most disastrous hazards and forbidding unreasonable human exploring activities in mountain areas. 相似文献
18.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
19.
对1995年至2001年《Natue》和《Science》上发表的天文学论文的统计表明,行星天文学领域的论文数量明显超过天文学的其它分支学科,占天文学总论文数的1/3左右。从这个角度来看,行星天文学是天文学最活跃和重要的分支学科之一。对这些论文具体内容的分析可以给出当前行星天文学领域的若干热点问题。相比之下,我国对这一重要领域的关注和投入还远远不够。 相似文献
20.