全文获取类型
收费全文 | 49530篇 |
免费 | 8647篇 |
国内免费 | 11577篇 |
专业分类
测绘学 | 3464篇 |
大气科学 | 10112篇 |
地球物理 | 12158篇 |
地质学 | 24356篇 |
海洋学 | 5868篇 |
天文学 | 2165篇 |
综合类 | 5419篇 |
自然地理 | 6212篇 |
出版年
2024年 | 240篇 |
2023年 | 846篇 |
2022年 | 2073篇 |
2021年 | 2498篇 |
2020年 | 2048篇 |
2019年 | 2360篇 |
2018年 | 2666篇 |
2017年 | 2424篇 |
2016年 | 2825篇 |
2015年 | 2334篇 |
2014年 | 2970篇 |
2013年 | 2851篇 |
2012年 | 2706篇 |
2011年 | 2851篇 |
2010年 | 2891篇 |
2009年 | 2794篇 |
2008年 | 2569篇 |
2007年 | 2453篇 |
2006年 | 1937篇 |
2005年 | 1926篇 |
2004年 | 1410篇 |
2003年 | 1436篇 |
2002年 | 1401篇 |
2001年 | 1416篇 |
2000年 | 1617篇 |
1999年 | 2307篇 |
1998年 | 1884篇 |
1997年 | 1877篇 |
1996年 | 1740篇 |
1995年 | 1509篇 |
1994年 | 1260篇 |
1993年 | 1158篇 |
1992年 | 911篇 |
1991年 | 716篇 |
1990年 | 544篇 |
1989年 | 483篇 |
1988年 | 425篇 |
1987年 | 265篇 |
1986年 | 237篇 |
1985年 | 166篇 |
1984年 | 143篇 |
1983年 | 116篇 |
1982年 | 99篇 |
1981年 | 82篇 |
1980年 | 78篇 |
1979年 | 58篇 |
1978年 | 24篇 |
1977年 | 22篇 |
1975年 | 16篇 |
1958年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
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
4.
Lin Liu 《Chinese Astronomy and Astrophysics》1997,21(4):488-500
With the aim of analyzing the errors in the radial position of satellites, we give in this paper the expressions for the radial perturbation which include the complete zeroth- and first-order terms in the orbital eccentricity. A simpler and faster method of calculating the perturbation is given. 相似文献
5.
Li Chongyin 《大气科学进展》1993,10(1):41-53
In a simple semi-geostropic model on the equatorialβ-plane, the theoretical analysis on the 30-60 day oscillation in the tropical atmosphere is further discussed based on the
wave-CISK mechanism. The convection heat-ing can excite the CISK-Kelvin wave and CISK-Rossby wave in the tropical atmosphere
and they are all the low-frequency modes which drive the activities of 30-60 day oscillation in the tropics. The most favorable
conditions to excite the CISK-Kelvin wave and CISK-Rossby wave are indicated: There is convection heating but not very strong
in the atmosphere and there is weaker disturbance in the lower troposphere.
The influences of vertical shearing of basic flow in the troposphere on the 30-60 day oscillation in the tropics are also
discussed. 相似文献
6.
PROPAGATION OF 30—60 DAY LOW FREQUENCY OSCILLATIONS AND THEIR INFLUENCE UPON THE SUBTROPICAL WESTERLIES JET STREAM DURING NORTHERN HEMISPHERE WINTER 下载免费PDF全文
Based on daily ECMWF gridpoint data of two winters during 1981—1983 including an ENSOyear,propagation of low frequency oscillations(LFO)during Northern Hemisphere winters andtheir influences upon 30—60 day oscillations of the subtropical jet stream are studied with the sta-tistical methods as complex empirical orthogonal function(CEOF)and so on.Results show that inthe winter of a normal year(1981—1982),30—60 day oscillations in the subtropical zone aremainly in the northern and southern flanks of exit region of jet stream.In the ENSO year(1982—1983),they are mainly in the vicinity of entrance and exit regions of jet stream.Intraseasonalchanges of subtropical jet stream manifested themselves as latitudinal fluctuation or longitudinalprogression or regression of about 40 day period.There are marked differences between propagat-ing passages of low frequency modes responsible for changes of subtropical jet stream in the normalyear(1981—1982)and in the ENSO year(1982—1983).Changes of oscillation amplitude showobvious phases.In general,the one in late winter is stronger than that in early winter,strongestone occurs in February. 相似文献
7.
8.
在文献」1「4 基础上,根据近年文选址实践中提出的问题,先进一步讨论了大气相干直径和时间的的物理和意义,然后强调了自由大气湍流的天文成像效应及选址中进行研究和测量的重要性。最后对差分像运动方法测量视宁度的定标和系统误差等问题作了分析。 相似文献
9.
Chun-sheng Li Qi-jun Fu Yu-hua Yan Shu-ying Jiang Hong-wei Li 《Chinese Astronomy and Astrophysics》1985,9(2):128-133
We propose a model of two acceleration regions, which can explain, on the basis of microwave maser caused by a “hollow-beam” distribution of electrons, the presence of millisecond spikes in the event of 1981 May 16 and their absence in the event of 1981 October 12, and the enhanced continuous emission in the latter. We have also uncovered relations among the features, e.g. the Type IIIG, Type IVDCIM and hard x-ray bursts, that accompany the microwave millisecond spikes during the impulsive phase of a large flare. 相似文献
10.
Quasi-electrostatic electron and ion-cyclotron instabilities are studied. The result indicates that the higher harmonic ion cyclotron instabilities (ICI) can be excited while the fast ions produced from reconnection are injected into a coronal loop. Part of the energetic ions can be dragged out of the magnetic mirror turning points and a negative plasma potential is generated. The plasma potential may directly accelerate the electrons up to the relativistic velocity within a short time. This acceleration is similar to the processes occurring in the magnetic mirror devices of controlled thermonuclear fusion. The spectrum and flux of accelerated electrons have also been obtained. Some observational results during the solar flare might be explained by this acceleration mechanism. 相似文献