全文获取类型
收费全文 | 7890篇 |
免费 | 353篇 |
国内免费 | 39篇 |
专业分类
测绘学 | 248篇 |
大气科学 | 520篇 |
地球物理 | 2675篇 |
地质学 | 2674篇 |
海洋学 | 453篇 |
天文学 | 1330篇 |
综合类 | 36篇 |
自然地理 | 346篇 |
出版年
2022年 | 56篇 |
2021年 | 137篇 |
2020年 | 147篇 |
2019年 | 120篇 |
2018年 | 316篇 |
2017年 | 295篇 |
2016年 | 437篇 |
2015年 | 326篇 |
2014年 | 373篇 |
2013年 | 462篇 |
2012年 | 395篇 |
2011年 | 395篇 |
2010年 | 345篇 |
2009年 | 406篇 |
2008年 | 349篇 |
2007年 | 246篇 |
2006年 | 269篇 |
2005年 | 242篇 |
2004年 | 207篇 |
2003年 | 204篇 |
2002年 | 169篇 |
2001年 | 147篇 |
2000年 | 151篇 |
1999年 | 106篇 |
1998年 | 135篇 |
1997年 | 104篇 |
1996年 | 72篇 |
1995年 | 83篇 |
1994年 | 100篇 |
1993年 | 59篇 |
1992年 | 67篇 |
1991年 | 53篇 |
1990年 | 73篇 |
1989年 | 53篇 |
1988年 | 52篇 |
1987年 | 45篇 |
1986年 | 47篇 |
1985年 | 60篇 |
1984年 | 43篇 |
1983年 | 61篇 |
1982年 | 57篇 |
1981年 | 47篇 |
1980年 | 52篇 |
1979年 | 53篇 |
1978年 | 58篇 |
1977年 | 45篇 |
1975年 | 48篇 |
1974年 | 37篇 |
1973年 | 47篇 |
1971年 | 42篇 |
排序方式: 共有8282条查询结果,搜索用时 0 毫秒
1.
Timothy Pietsch Justine Kemp Colin Pardoe Rainer Grün Jon Olley Rachel Wood 《第四纪科学杂志》2019,34(8):662-673
Kiacatoo Man, a large, rugged Aboriginal adult buried in the Lachlan riverine plains of southeastern Australia, was discovered in 2011. Laser‐ablation uranium series analysis on bone yielded a minimum age for the burial of 27.4 ± 0.4 ka (2σ). Single‐grain, optically stimulated luminescence ages on quartz sediment in which the grave had been dug gave a weighted mean age of 26.4 ± 1.5 ka (1σ). Luminescence samples from the grave infill and from sediment beneath the grave exhibit overdispersed dose distributions consistent with bioturbation or other disturbance, which has obscured the burial signal. The overlap between the minimum (U‐series) and maximum (luminescence) ages places the burial between 27.0 and 29.4 ka (2σ). Luminescence ages obtained from the channel belt of between 28 ± 2 and 25 ± 3 ka indicate that fluvial sedimentation was occurring before the Last Glacial Maximum, which is consistent with the broader geomorphic setting. Together, these results are internally and regionally consistent, and indicate that Kiacatoo Man was one of the more ancient individuals so far identified in Australia. His remains are important to our understanding of patterns of biological variation and other processes that have shaped people in the Murray‐Darling Basin through time. Copyright © 2019 John Wiley & Sons, Ltd. 相似文献
2.
Micromechanical approach to effective viscoelastic properties of micro‐fractured geomaterials
下载免费PDF全文
![点击此处可从《国际地质力学数值与分析法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The aim of this paper is to formulate a micromechanics‐based approach to non‐aging viscoelastic behavior of materials with randomly distributed micro‐fractures. Unlike cracks, fractures are discontinuities that are able to transfer stresses and can therefore be regarded from a mechanical viewpoint as interfaces endowed with a specific behavior under normal and shear loading. Making use of the elastic‐viscoelastic correspondence principle together with a Mori‐Tanka homogenization scheme, the effective viscoelastic behavior is assessed from properties of the material constituents and damage parameters related to density and size of fractures. It is notably shown that the homogenized behavior thus formulated can be described in most cases by means of a generalized Maxwell rheological model. For practical implementation in structural analyses, an approximate model for the isotropic homogenized fractured medium is formulated within the class of Burger models. Although the approximation is basically developed for short‐term and long‐term behaviors, numerical applications indicate that the approximate Burger model accurately reproduce the homogenized viscoelastic behavior also in the transient conditions. 相似文献
3.
Zsolt Sándor Bálint Érdi Carl D. Murray 《Celestial Mechanics and Dynamical Astronomy》2002,84(4):355-368
The dynamics of co-orbital motion in the restricted three-body problem are investigated by symplectic mappings. Analytical and semi-numerical mappings have been developed and studied in detail. The mappings have been tested by numerical integration of the equations of motion. These mappings have been proved to be useful for a quick determination of the phase space structure reflecting the main characteristics of the dynamics of the co-orbital problem. 相似文献
4.
5.
We report intermediate resolution H spectroscopy of the black hole candidate Nova Muscae 1991 during quiescence. We classify the companion star as a K3-K4V which contributes 85±6 percent to the total flux from the binary. The photospheric absorption lines are broadened by 106±13 kms−1 with respect to template field stars, leading to a system mass ratio of q =M1/M2 = 7.8−2.0+3.4. Doppler imaging of the H line shows strong emission coming from the secondary star (EW=3.1±0.6Å) which we associate with chromospheric activity. However, the hot-spot is not detected and this may indicate a lower mass transfer rate than in other X-ray transients of comparable orbital periods. The surface brightness distribution of the accretion disk in H follows a relation I∝R−1.1, less steep than typically observed in cataclysmic variables. Updated system parameters are also presented. 相似文献
6.
Attila Mészáros 《Astrophysics and Space Science》1985,111(2):399-405
Graviton may, in principle, have a small non-zero mass. In this paper the relevant theory of the massive graviton with six polarisations is developed. The drastic impact of a non-zero mass of the graviton on cosmology is also illustrated. 相似文献
7.
J.C. Vega Beltrán W.W. Zeilinger A. Pizzella E.M. Corsini F. Bertola J.G. Funes J.E. Beckman 《Astrophysics and Space Science》2001,276(2-4):1201-1210
In this paper we present the kinematics of the gas and/or the stars of a sample of 20 disc galaxies. We investigate whether there is any relation between the kinematics of the gas and stars and the classical morphological type of the galaxies in the sample. We deduce that, in most of the late-type spirals we have studied, the stars and the ionized gas are moving with virtually circular velocity, except when the spectroscopic slit crosses a bar region. On the other hand, we found in the central parts of early-type disc galaxies a wider variety of different behaviour of stars and gas. We find many possible factors that complicate the classification of the kinematical properties of the galaxies by their morphological type: the presence of counter-rotations (star vs. stars or star vs. gas), misalignment between the different kinematic components present in the galaxy, the presence of a bar structure and its orientation with respect to the line of nodes of the galaxy, and interactions and mergers or external accretion processes are some of the problems we find in the study of the kinematics of a galaxy. 相似文献
8.
9.
Exact solutions of the semi-classical Einstein equations for conformally invariant free quantum fields in an homogeneous and
isotropic space-time, with cosmological constant and containing a classical scalar field, dust matter, an unquantised Dirac
field and electromagnetic radiation are found. The initial behaviour of the semiclassical models is investigated. Some of
the solutions found avoid the singularity and do not have particle horizons.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
The trans-Neptunian belt has been subject to a strong depletion that has reduced its primordial population by a factor of one hundred over the solar system's age. One by-product of such a depletion process is the existence of a scattered disk population in transit from the belt to other places, such as the Jupiter zone, the Oort cloud or interstellar space. We have integrated the orbits of the scattered disk objects (SDOs) so far discovered by 2500 Myr to study their dynamical time scales and the probability of falling in each of the end states mentioned above, paying special attention to their contribution to the Oort cloud. We found that their dynamical half-time is close to 2.5 Gyr and that about one third of the SDOs end up in the Oort cloud. 相似文献