全文获取类型
收费全文 | 10374篇 |
免费 | 1711篇 |
国内免费 | 2564篇 |
专业分类
测绘学 | 928篇 |
大气科学 | 2334篇 |
地球物理 | 2718篇 |
地质学 | 2941篇 |
海洋学 | 2543篇 |
天文学 | 1048篇 |
综合类 | 551篇 |
自然地理 | 1586篇 |
出版年
2024年 | 51篇 |
2023年 | 112篇 |
2022年 | 279篇 |
2021年 | 363篇 |
2020年 | 390篇 |
2019年 | 512篇 |
2018年 | 416篇 |
2017年 | 462篇 |
2016年 | 427篇 |
2015年 | 470篇 |
2014年 | 580篇 |
2013年 | 772篇 |
2012年 | 521篇 |
2011年 | 589篇 |
2010年 | 533篇 |
2009年 | 754篇 |
2008年 | 773篇 |
2007年 | 836篇 |
2006年 | 710篇 |
2005年 | 593篇 |
2004年 | 580篇 |
2003年 | 508篇 |
2002年 | 474篇 |
2001年 | 366篇 |
2000年 | 362篇 |
1999年 | 344篇 |
1998年 | 312篇 |
1997年 | 227篇 |
1996年 | 247篇 |
1995年 | 170篇 |
1994年 | 155篇 |
1993年 | 153篇 |
1992年 | 125篇 |
1991年 | 105篇 |
1990年 | 88篇 |
1989年 | 63篇 |
1988年 | 46篇 |
1987年 | 41篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
31.
32.
Miniature gravity corer for recovering short sediment cores 总被引:12,自引:0,他引:12
John R. Glew 《Journal of Paleolimnology》1991,5(3):285-287
33.
In this paper the second order characteristic (discontinuous bifurcation) condition is derived for the granular flow (fully plastic) equations. This second order bifurcation equation is shown to be formally identical to the first order localization requirement during steady elastoplastic deformation provided the elastic compliance tensor is substituted for the product of the plastic multiplier with the flow Hessian. For isotropic yield and flow functions the invariant form of the characteristic condition is given in detail, as well as an alternative expression in adapted co‐ordinates. The characteristic condition can be regarded as defining a hardening function which is maximized to identify the critical angles. When the method is applied to 3D Coulomb flow, Mohr's 3D fracture plane conditions are obtained uniquely. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
34.
In this paper, we present 50 surface water samples collected during the IMAGES III cruise (June–July 1997) along a transect from New Zealand to the China Sea (42°S–178°E, 21°N–120°E) covering a temperature range from 13.3 to 30.4 °C. A very worthwhile aspect of this study is a coupling of both biomarker (alkenone) and coccolithophorid counting. We show that the U37k′–temperature relationship is very similar to the Prahl et al. [Geochim. Cosmochim. Acta 52 (1988) 2203] culture calibration and to the global core top calibration of Müller et al. [Geochim. Cosmochim. Acta 62 (1998) 1757]. However, in the warmest surface waters of the Western Pacific ocean (>26.4 °C) where Gephyrocapsa oceanica is likely the most widespread species, the associated U37k′ has a constant value of 1.0. The consequence is that above this temperature threshold, U37k′ cannot be used as an accurate paleothermometer. 相似文献
35.
36.
37.
Burkhard Fuchs 《Astrophysics and Space Science》2003,284(2):719-722
An update of the set of low surface brightness galaxies is presented which can be used to set constraints on the otherwise
ambiguous decompositions of their rotation curves into contributions due to the various components of the galaxies. The selected
galaxies show all clear spiral structure and arguments of density wave theory of galactic spiral arms are used to estimate
the masses of the galactic disks. Again these estimates seem to indicate that the disks of low surface brightness galaxies
might be much more massive than currently thought. This puzzling result contradicts stellar population synthesis models. This
would mean also that low surface brightness galaxies are not dominated by dark matter in their inner parts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
38.
39.
The effect of particle-particle interaction on the adiabatic index γ for an electron-positron plasma is considered. An improved method for numerically calculating the Hartree-Fock exchange integral is presented and its relativistic asymptotics is determined. An approximation formula is derived for the correlation part of the interaction in the low-density limit. This formula includes degeneracy and the positron component. 相似文献
40.
S. A. Petrova 《Monthly notices of the Royal Astronomical Society》2006,368(4):1764-1772
Pulsar radio emission is modelled as a sum of two completely polarized non-orthogonal modes with the randomly varying Stokes parameters and intensity ratio. The modes are the result of polarization evolution of the original natural waves in the hot, magnetized, weakly inhomogeneous plasma of the pulsar magnetosphere. In the course of the wavemode coupling, the linearly polarized natural waves acquire purely orthogonal elliptical polarizations. Further on, as the waves pass through the cyclotron resonance, they become non-orthogonal. The pulse-to-pulse fluctuations of the final polarization characteristics and the intensity ratio of the modes are attributed to the temporal fluctuations in the plasma flow.
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献
The model suggested allows one to reproduce the basic features of the one-dimensional distributions of the individual-pulse polarization characteristics. Besides that, the propagation origin of the pulsar polarization implies a certain correlation between the mode ellipticity and position angle. On a qualitative level, for different sets of parameters, the expected correlations appear compatible with the observed ones. Further theoretical studies are necessary to establish the quantitative correspondence of the model to the observational results and to develop a technique of diagnostics of the pulsar plasma on this basis. 相似文献