全文获取类型
收费全文 | 38217篇 |
免费 | 1154篇 |
国内免费 | 1058篇 |
专业分类
测绘学 | 978篇 |
大气科学 | 3028篇 |
地球物理 | 7893篇 |
地质学 | 14197篇 |
海洋学 | 3369篇 |
天文学 | 8268篇 |
综合类 | 246篇 |
自然地理 | 2450篇 |
出版年
2022年 | 293篇 |
2021年 | 496篇 |
2020年 | 481篇 |
2019年 | 518篇 |
2018年 | 950篇 |
2017年 | 905篇 |
2016年 | 1109篇 |
2015年 | 768篇 |
2014年 | 1108篇 |
2013年 | 1939篇 |
2012年 | 1400篇 |
2011年 | 1858篇 |
2010年 | 1621篇 |
2009年 | 2082篇 |
2008年 | 1748篇 |
2007年 | 1805篇 |
2006年 | 1750篇 |
2005年 | 1263篇 |
2004年 | 1168篇 |
2003年 | 1059篇 |
2002年 | 1029篇 |
2001年 | 867篇 |
2000年 | 836篇 |
1999年 | 690篇 |
1998年 | 727篇 |
1997年 | 700篇 |
1996年 | 580篇 |
1995年 | 566篇 |
1994年 | 483篇 |
1993年 | 427篇 |
1992年 | 424篇 |
1991年 | 390篇 |
1990年 | 464篇 |
1989年 | 378篇 |
1988年 | 358篇 |
1987年 | 440篇 |
1986年 | 347篇 |
1985年 | 434篇 |
1984年 | 535篇 |
1983年 | 454篇 |
1982年 | 452篇 |
1981年 | 403篇 |
1980年 | 420篇 |
1979年 | 361篇 |
1978年 | 345篇 |
1977年 | 340篇 |
1976年 | 310篇 |
1975年 | 297篇 |
1974年 | 313篇 |
1973年 | 340篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
The present work applies the method of characteristics to study the behaviour of planar and cylindrical wave-heads propagating through a perfectly electrically conducting and thermally radiating inviscid gas under the optically thin limit in the presence of a transverse magnetic field. The true nonlinear progress of the flow variable gradients at the wavefront is predicted and the critical distance at which the characteristics pile up at the wavefront to form a shock wave is obtained. It is investigated as to how the effects of radiative flux, the magnetic field strength and the specific heat ratio influence the process of steepening or flattening of the characteristic wavefront. 相似文献
112.
The paper models the suprathermal plasma as the concatenation of two different gravitating fluids each having its own separate density and pressure. One of the fluids has isotropic pressure while the other has an anisotropic pressure. The system is subjected to a uniform magnetic field which is frozen with the fluids. The gravitational instability of the model for low frequency plane waves has been investigated in a linear framework for plasma parameters relevant to the spiral arms of the galaxy and the cosmic gas clouds. The analysis shows that the wavelength of the instability is strongly dependent upon the anisotropy of the non-thermal plasma. 相似文献
113.
J. CAMPSIE M. H. RASMUSSEN L. C. KOVACS F. DITTMER J. C. BAILEY N. O. HANSEN J. LAURSEN L. JOHNSON 《Polar research》1990,8(2):237-243
New aeromagnetic data, K-Ar age determinations of dredged marine igneous rocks, as well as other geophysical evidence have shed light on the chronology, nature and evolution of the northern Iceland Plateau. Correspondence between seismic refraction profiles taken on the Jan Mayen Ridge and westward through Jan Mayen Island, suppressed aeromagnetic anomalies, earthquake surface wave studies, and ages of dredged igneous rocks suggest these strata may form an extended region of thickened crust, possibly of Caledonian age, extending westward toward the Kolbeinsey Ridge and northwest to the south wall of the Jan Mayen Fracture Zone. 相似文献
114.
Summary We present compositions of reheated melt inclusions in clinopyroxene phenocrysts from three mafic xenoliths in Breccia Museo,
Campi Flegrei, Italy. Melt inclusion compositions are remarkably different from the compositions of known contemporary Campi
Flegrei lavas, being significantly enriched in K2O and depleted in Na2O. Some differences are also evident in FeO* (total Fe as FeO) and TiO2 contents. The clinopyroxene phenocrysts could not have crystallised from Campi Flegrei magmas. We suggest that they originated
from a volcanic system genetically very similar to, and possibly linked with, the >14 ka volcanic system of Mt. Somma, another
Campanian volcano ∼ 30 km east from Campi Flegrei, from which Vesuvius subsequently developed. This result indicates a close
relationship (or link) between the two volcanic systems which have until now been considered separate. We speculate that the
link was established prior to eruption of the Neapolitan Yellow Tuff (NYT) (∼ 12 ka). The xenoliths were derived from a volcanic
system older than the host breccias themselves. We suggest that this older volcanism had close similarities with the volcanism
of the older products of Mt. Somma (∼25 ka).
Received March 20, 2000; accepted November 2, 2000 相似文献
115.
M. L. Demidov 《Solar physics》1996,164(1-2):381-388
The zero level problem of solar magnetographs is particularly important for observations of large-scale magnetic fields on the Sun. Experiments conducted at the STOP telescope of the Sayan observatory show that, in addition to adjustment errors of the polarization analyzer and the spectrograph focusing, spurious signals of the magnetograph are caused by polarization effects in optical components preceding the polarization analyzer and aberration errors of the spectrograph. 相似文献
116.
117.
L. A. L. Da Silva 《Astrophysics and Space Science》1990,165(2):255-260
A comparison is made of the light and colour curves of the SN 1987A in the first 280 days with the mean properties of type II supernovae. The conclusion is that even though it has H lines, and was not a typical type II supernova, but a peculiar object from a photometric point of view. The implications for inclusion of SN 1987A in the context of the usual Minkowski-Zwicky classification are explicitly discussed. 相似文献
118.
S. D. Doty R. A. Metzler M. L. Palotti 《Monthly notices of the Royal Astronomical Society》2005,362(2):737-747
We present a study of radiative transfer in dusty, clumpy star-forming regions. A series of self-consistent, 3D, continuum radiative transfer models are constructed for a grid of models parametrized by central luminosity, filling factor, clump radius and face-averaged optical depth. The temperature distribution within the clouds is studied as a function of this parametrization. Among our results, we find that: (i) the effective optical depth in clumpy regions is less than in equivalent homogeneous regions of the same average optical depth, leading to a deeper penetration of heating radiation in clumpy clouds, and temperatures higher by over 60 per cent; (ii) penetration of radiation is driven by the fraction of open sky (FOS) – which is a measure of the fraction of solid angle along which no clumps exist; (iii) FOS increases as clump radius increases and as filling factor decreases; (iv) for values of FOS >0.6–0.8 the sky is sufficiently 'open' that the temperature distribution is relatively insensitive to FOS; (v) the physical process by which radiation penetrates is preferentially through streaming of radiation between clumps as opposed to diffusion through clumps; (vi) filling factor always dominates the determination of the temperature distribution for large optical depths, and for small clump radii at smaller optical depths; (vii) at lower face-averaged optical depths, the temperature distribution is most sensitive to filling factors of 1–10 per cent, in accordance with many observations; (viii) direct shadowing by clumps can be important for distances approximately one clump radius behind a clump. 相似文献
119.
This paper presents two and three dimensional simulations of the interaction of shocks with media with large numbers of dense
inclusions. An approximate model of the interaction of a starburst wind with the surrounding galactic ISM illustrates issues
which must be addressed in global models of ISM dynamics. As a step towards developing the sub-grid model of multiphase turbulence,
we define and study a form of ‘multiphase Riemann problem’. This allows us to develop macroscopic characteristics of the flows
which may be compared to such subgrid models. 相似文献