全文获取类型
收费全文 | 65170篇 |
免费 | 22601篇 |
国内免费 | 47208篇 |
学科分类
地球科学 | 134979篇 |
出版年
2024年 | 296篇 |
2023年 | 836篇 |
2022年 | 1954篇 |
2021年 | 2473篇 |
2020年 | 3226篇 |
2019年 | 6702篇 |
2018年 | 7095篇 |
2017年 | 6678篇 |
2016年 | 7057篇 |
2015年 | 6089篇 |
2014年 | 6014篇 |
2013年 | 6542篇 |
2012年 | 6077篇 |
2011年 | 5995篇 |
2010年 | 5884篇 |
2009年 | 5241篇 |
2008年 | 4384篇 |
2007年 | 4342篇 |
2006年 | 3766篇 |
2005年 | 3607篇 |
2004年 | 3535篇 |
2003年 | 3268篇 |
2002年 | 2964篇 |
2001年 | 2837篇 |
2000年 | 2652篇 |
1999年 | 3082篇 |
1998年 | 2806篇 |
1997年 | 2782篇 |
1996年 | 2358篇 |
1995年 | 2189篇 |
1994年 | 1927篇 |
1993年 | 1779篇 |
1992年 | 1470篇 |
1991年 | 1163篇 |
1990年 | 1006篇 |
1989年 | 883篇 |
1988年 | 761篇 |
1987年 | 519篇 |
1986年 | 465篇 |
1985年 | 347篇 |
1984年 | 368篇 |
1983年 | 231篇 |
1982年 | 248篇 |
1981年 | 188篇 |
1980年 | 148篇 |
1979年 | 129篇 |
1978年 | 57篇 |
1977年 | 52篇 |
1971年 | 53篇 |
1958年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
Maarten A. Prins Hongbo Zheng Kay Beets Simon Troelstra Patrick Bacon Ilse Kamerling Wouter Wester Martin Konert Xiangtong Huang Wang Ke Jef Vandenberghe 《第四纪科学杂志》2009,24(1):75-84
The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
4.
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
5.
6.
Dynamic analysis of three-dimensional marine cables 总被引:1,自引:0,他引:1
Shan Huang 《Ocean Engineering》1994,21(6)
Marine cables are widely used in a variety of offshore activities. In this paper, a numerical approach is presented which is capable of predicting the dynamic behaviour of three-dimensional marine cables. The solution of this problem is of practical importance in the estimation of dybamic loading and motion, and thus has direct application to the enhancement of safety and the effectiveness of the offshore activities. The approach is based upon the lump-mass-and-spring model and the finite difference method. Mathematical analysis is provided on the basic characteristics of the model and the numerical stability. A numerical example is given to demonstrate the validity of the approach. 相似文献
7.
8.
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
9.
Ren Tinawi Marc Sarrazin Andr Filiatrault 《Soil Dynamics and Earthquake Engineering》1993,12(8):469-477
The 1990 edition of the National Building Code of Canada (Associate Committee of the National Building Code, National Research Council, Ottawa, 1990) makes a clear distinction between eastern and western Canada in terms of seismic acceleration and velocity zones. While it is well established that ground motions can be amplified significantly through loose clay deposits, no results are available that take into consideration the typical high frequency content of ground motions in eastern Canada. This paper develops ground amplification curves for clays having depths between 10 and 70 m excited by typical eastern Canadian ground motions scaled to two different values of peak horizontal accelerations. Simplified free-field spectral design curves, which could be used by structural designers, are proposed. The curves show that maximum spectral accelerations occur for structural periods between 0.2 and 0.5 s. In addition, soil depth does not appear to be an important parameter controlling the response of typical clay deposits in eastern Canada. 相似文献
10.
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