全文获取类型
收费全文 | 4104篇 |
免费 | 282篇 |
国内免费 | 138篇 |
专业分类
测绘学 | 260篇 |
大气科学 | 339篇 |
地球物理 | 1119篇 |
地质学 | 1626篇 |
海洋学 | 243篇 |
天文学 | 655篇 |
综合类 | 79篇 |
自然地理 | 203篇 |
出版年
2023年 | 22篇 |
2022年 | 43篇 |
2021年 | 89篇 |
2020年 | 92篇 |
2019年 | 82篇 |
2018年 | 207篇 |
2017年 | 167篇 |
2016年 | 257篇 |
2015年 | 212篇 |
2014年 | 252篇 |
2013年 | 294篇 |
2012年 | 232篇 |
2011年 | 250篇 |
2010年 | 233篇 |
2009年 | 222篇 |
2008年 | 181篇 |
2007年 | 146篇 |
2006年 | 135篇 |
2005年 | 113篇 |
2004年 | 110篇 |
2003年 | 82篇 |
2002年 | 84篇 |
2001年 | 81篇 |
2000年 | 56篇 |
1999年 | 47篇 |
1998年 | 77篇 |
1997年 | 53篇 |
1996年 | 45篇 |
1995年 | 43篇 |
1994年 | 45篇 |
1993年 | 31篇 |
1992年 | 35篇 |
1991年 | 26篇 |
1990年 | 39篇 |
1989年 | 31篇 |
1988年 | 26篇 |
1987年 | 16篇 |
1986年 | 26篇 |
1985年 | 25篇 |
1983年 | 24篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 15篇 |
1978年 | 16篇 |
1977年 | 20篇 |
1974年 | 15篇 |
1973年 | 14篇 |
1971年 | 15篇 |
1968年 | 14篇 |
排序方式: 共有4524条查询结果,搜索用时 15 毫秒
1.
Revisiting the existence of an effective stress for wet granular soils with micromechanics 下载免费PDF全文
A possible effective stress variable for wet granular materials is numerically investigated based on an adapted discrete element method (DEM) model for an ideal three‐phase system. The DEM simulations consider granular materials made of nearly monodisperse spherical particles, in the pendular regime with the pore fluid mixture consisting of distinct water menisci bridging particle pairs. The contact force‐related stress contribution to the total stresses is isolated and tested as the effective stress candidate for dense or loose systems. It is first recalled that this contact stress tensor is indeed an adequate effective stress that describes stress limit states of wet samples with the same Mohr‐Coulomb criterion associated with their dry counterparts. As for constitutive relationships, it is demonstrated that the contact stress tensor used in conjunction with dry constitutive relations does describe the strains of wet samples during an initial strain regime but not beyond. Outside this so‐called quasi‐static strain regime, whose extent is much greater for dense than loose materials, dramatic changes in the contact network prevent macroscale contact stress‐strain relationships to apply in the same manner to dry and unsaturated conditions. The presented numerical results also reveal unexpected constitutive bifurcations for the loose material, related to stick‐slip macrobehavior. 相似文献
2.
D. Montes M. C. Gálvez M. J. Fernández-Figueroa I. Crespo-Chacón 《Astrophysics and Space Science》2006,304(1-4):367-369
High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D1&D2, He i D3, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics. 相似文献
3.
4.
Sediment successions in coastal cliffs around Mezen Bay, southeastern White Sea, record an unusually detailed history of former glaciations, interstadial marine and fluvial events from the Weichselian. A regional glaciation model for the Weichselian is based on new data from the Mezen Bay area and previously published data from adjacent areas. Following the Mikulinian (Eemian) interglacial a shelf‐centred glaciation in the Kara Sea is reflected in proglacial conditions at 100–90 ka. A local ice‐cap over the Timan ridge existed between 75 and 65 ka. Renewed glaciation in the Kara Sea spread southwestwards around 60 ka only, interrupted by a marine inundation, before it advanced to its maximum position at about 55–50 ka. After a prolonged ice‐free period, the Scandinavian ice‐sheet invaded the area from the west and terminated east of Mezen Bay about 17 ka. The previously published evidence of a large ice‐dammed lake in the central Arkhangelsk region, Lake Komi, finds no support in this study. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
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
6.
R. Vílchez-Gómex G. A. Bruzual R. Pelló R. Domínguez 《Astrophysics and Space Science》2001,276(2-4):757-764
We have developed model predictions for the morphological distribution of cluster galaxies as a function of the cluster-centric
distance and the local galaxy density, using a semi-analytical code. This code allows us to obtain magnitudes and colours
for cluster galaxies at different redshifts, and thus to study in detail the evolution of the colour–magnitude relation of
specific distant clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
8.
Vladimír Skalský 《Astrophysics and Space Science》1993,201(1):3-14
(a) Hubble's discovery of the expansion of the Universe makes it possible to choose unambiguously from the models described by Friedmann's equations of universe dynamics. (b) From the present temperature of the cosmic microwave background radiation, the specific entropy in the matter era and the model properties of the expansive nondecelerative universe, we can determine the present parameters of our Universe with deviations smaller than 2.2%. 相似文献
9.
10.
The aim of the present paper is to analyze the light variation as well as the period changes of the eclipsing binary RZ Cas. New photometric elements are computed using the frequency-domain method. The possibility of the light-time effect and the apsidal motion is discussed. 相似文献