全文获取类型
收费全文 | 40251篇 |
免费 | 7066篇 |
国内免费 | 9636篇 |
学科分类
地球科学 | 56953篇 |
出版年
2024年 | 210篇 |
2023年 | 695篇 |
2022年 | 1773篇 |
2021年 | 2088篇 |
2020年 | 1696篇 |
2019年 | 2019篇 |
2018年 | 2183篇 |
2017年 | 1981篇 |
2016年 | 2328篇 |
2015年 | 1994篇 |
2014年 | 2508篇 |
2013年 | 2311篇 |
2012年 | 2224篇 |
2011年 | 2388篇 |
2010年 | 2441篇 |
2009年 | 2303篇 |
2008年 | 2150篇 |
2007年 | 2053篇 |
2006年 | 1587篇 |
2005年 | 1468篇 |
2004年 | 1179篇 |
2003年 | 1184篇 |
2002年 | 1151篇 |
2001年 | 1157篇 |
2000年 | 1336篇 |
1999年 | 1790篇 |
1998年 | 1460篇 |
1997年 | 1408篇 |
1996年 | 1280篇 |
1995年 | 1119篇 |
1994年 | 1041篇 |
1993年 | 912篇 |
1992年 | 712篇 |
1991年 | 567篇 |
1990年 | 425篇 |
1989年 | 380篇 |
1988年 | 352篇 |
1987年 | 197篇 |
1986年 | 184篇 |
1985年 | 131篇 |
1984年 | 128篇 |
1983年 | 101篇 |
1982年 | 97篇 |
1981年 | 81篇 |
1980年 | 48篇 |
1979年 | 42篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1958年 | 34篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 46 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.
Stress wave attenuation across fractured rock masses is a great concern of underground structure safety. When the wave amplitude is large, fractures experience nonlinear deformation during the wave propagation. This paper presents a study on normal transmission of P‐wave across parallel fractures with nonlinear deformational behaviour (static Barton–Bandis model). The results show that the magnitude of transmission coefficient is a function of incident wave amplitude, nondimensional fracture spacing and number of fractures. Two important indices of nondimensional fracture spacing are identified, and they divide the area of nondimensional fracture spacing into three parts (individual fracture area, transition area and small spacing area). In the different areas, the magnitude of transmission coefficient has different trends with nondimensional fracture spacing and number of fractures. In addition, the study reveals that under some circumstances, the magnitude of transmission coefficient increases with increasing number of fractures, and is larger than 1. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
5.
Based on the CN and C2 comae isophotes for two comets (1961 IX and 1970 16) given by Rahe et al. and the relevant theory of physical chemistry, we have deduced the distributions of the CN and C2 modecules in the coma, their scale heights and mean lifetimes. The results favour the viewpoint that HCN is the parent of CN, and that C2H2 is the parent of C2. 相似文献
6.
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
7.
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
8.
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.
Zhao Yiyang 《中国海洋湖沼学报》1985,3(2):200-211
Geochemical patterns of shelf sediments of China Seas are discussed in the following order: 1) the grain-size control of elements,
2) zonal distribution of elements along the coast, 3) estuarine enrichment of elements, 4) correlation of elements, 5) philo-detrital
property of elements, 6) philo-continental property of elements, 7) rapid accumulation rate of elements. Statistics show that
the abundance of indicator elements in shelf sediments is relatively close to that in terrestrial rocks and continental crust,
and the abundance distribution pattern of elements in shelf sediments is similar to that in continental crust. 相似文献