全文获取类型
收费全文 | 100516篇 |
免费 | 1553篇 |
国内免费 | 915篇 |
专业分类
测绘学 | 2491篇 |
大气科学 | 7124篇 |
地球物理 | 20117篇 |
地质学 | 35341篇 |
海洋学 | 8864篇 |
天文学 | 22678篇 |
综合类 | 267篇 |
自然地理 | 6102篇 |
出版年
2022年 | 509篇 |
2021年 | 967篇 |
2020年 | 1061篇 |
2019年 | 1144篇 |
2018年 | 2505篇 |
2017年 | 2304篇 |
2016年 | 2957篇 |
2015年 | 1714篇 |
2014年 | 2831篇 |
2013年 | 5295篇 |
2012年 | 3040篇 |
2011年 | 4135篇 |
2010年 | 3568篇 |
2009年 | 4779篇 |
2008年 | 4289篇 |
2007年 | 4131篇 |
2006年 | 3883篇 |
2005年 | 3177篇 |
2004年 | 3139篇 |
2003年 | 2950篇 |
2002年 | 2785篇 |
2001年 | 2500篇 |
2000年 | 2385篇 |
1999年 | 1941篇 |
1998年 | 2033篇 |
1997年 | 1953篇 |
1996年 | 1599篇 |
1995年 | 1603篇 |
1994年 | 1398篇 |
1993年 | 1305篇 |
1992年 | 1240篇 |
1991年 | 1152篇 |
1990年 | 1226篇 |
1989年 | 1113篇 |
1988年 | 1029篇 |
1987年 | 1245篇 |
1986年 | 1067篇 |
1985年 | 1322篇 |
1984年 | 1440篇 |
1983年 | 1321篇 |
1982年 | 1264篇 |
1981年 | 1182篇 |
1980年 | 1043篇 |
1979年 | 986篇 |
1978年 | 971篇 |
1977年 | 926篇 |
1976年 | 862篇 |
1975年 | 820篇 |
1974年 | 822篇 |
1973年 | 803篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
J. J. Quenby T. J Sumner S. D. Sidher S. Immler 《Astrophysics and Space Science》1994,216(1-2):213-217
The shadowing effects of the molecular clouds in the nearby interstellar medium on the soft x-ray background has been investigated, using ROSAT WFC data in conjunction with previous rocket B and C band surveys. Shadowing over a 5° extent occurs only for a few percent of the sky, but the mixed model of the ISM is supported.Detailed modelling of the Draco shadowing region shows little evidence for a multi-temperature, hot ISM component. 相似文献
152.
153.
We present a simple model for the formation and growth of photochemical aerosols in the atmosphere of Titan. We show that, in general, an optically thick layer of particles in the size range required by models of Titan cannot be obtained at pressures less than about 2 mbar. Since the thin model of Titan's atmosphere requires that the inversion not extend below pressures of 0.11 mbar (D. M. Hunten and J. J. Caldwell, 1978, preprint), it seems to be ruled out by the calculations. 相似文献
154.
155.
Donald D. Clayton 《Icarus》1977,32(3):255-269
I evaluate several nuclear and chemical problems related both to the recent scenario suggesting that the known isotopic anomalies in the solar system have resulted from a supernova near the protosolar nebula and to the model of extinct presolar carriers. Major features include: (1) Large quantities of extinct 248Cm and 36Cl are predicted from the Cameron-Truran model of a minor injection about 106 yr before condensation; (2) an extinct-carrier model of 26Mg is set forth in detail with a solid chemistry picture of the early solar system; (3) a major thermonuclear supernova responsible for 26Al, 244Pu, and 40K would have to have occurred several million years (3 m.y.) before condensation and contributed a large fraction of the major stable chemical elements; (4) carbon isotope families are to be expected if the oxygen isotope families are due to a late injection of 16O; (5) the Earth and E meteorites may have condensed primarily in a carbon-rich nebula existing before admixtures of a major late 16O-rich mixture; (6) the extinct-presolar-carrier model is the single best explanation of all anomalies. 相似文献
156.
Green's Theorem is developed for the spherically-symmetric steady-state cosmic-ray equation of transport in interplanetary space. By means of it the momentum distribution functionF
o(r,p), (r=heliocentric distance,p=momentum) can be determined in a regionr
arrbwhen a source is specified throughout the region and the momentum spectrum is specified on the boundaries atr
a
andr
b
. Evaluation requires a knowledge of the Green's function which corresponds to the solution for monoenergetic particles released at heliocentric radiusr
o
, Examples of Green's functions are given for the caser
a
=0,r
b
= and derived for the cases of finiter
a
andr
b
. The diffusion coefficient is assumed of the form = o(p)r
b
. The treatment systematizes the development of all analytic solutions for steady-state solar and galactic cosmic-ray propagation and previous solutions form a subset of the present solutions. 相似文献
157.
In the present paper, H-evolutive curves of chromospheric events are compared with flux evolutive curves of X-ray events observed at the same time in different spectral regions. A correspondence between the emissions E(I
H/I
chr)'s at higher and higher H-intensity levels, and the X-ray fluxes F()'s in harder and harder -ranges is shown. Further, the present observations seem to indicate the existence of a single triggering mechanism during the flash-phase of a flare. It is also shown that these results may be in agreement with Brown's model for chromospheric flares. 相似文献
158.
C. D'uston J. M. Bosqued F. Cambou V. V. Temny G. N. Zastenker O. L. Vaisberg E. G. Eroshenko 《Solar physics》1977,51(1):217-229
Solar wind and interplanetary magnetic field data were obtained by the PROGNOZ 1 and PROGNOZ 2 satellites during the period following the August 4, 1972 (0621 UT) solar flare. A thermalized plasma was recorded one hour after the shock followed two hours later by the plasma piston with a bulk velocity higher than 1700 km s-1. The comparison between the PROGNOZ and PIONEER 9 solar wind data shows an attenuation of the plasma properties with the deflection from the flare's meridian. 相似文献
159.
Photographs of the corona in the continuum spectrum (580–700 nm) have been obtained with a doublet camera (F=4m) through rotating sector polarizers with the vibrational directions oriented radially and tangentially to the solar limb. Isophotes of the total emission and its polarized component, as well as diagrams giving the degree of polarization for the (K+F)-corona and the electron corona proper (P
K), have been plotted up to the distance of 1R
from the limb. In some inner regions the polarizationP
K exceeds the highest value possible for Thomson scattering under the given conditions. The reality of this anomally is dubious; systematic photometrical errors may account for it. Three-dimensional forms of 15 different coronal rays have been ascertained by comparing the course of polarization along the rays to the family of Baumach curves. The rays are found to deflect substantially from the radial directions out of the plane of the sky. Mean values of the coronal brightness and polarization versus the distance from the Sun have been determined. Contrary to well-known models (Van de Hulst) the mean polarization of the electron corona (P
K) decreases with distance after reaching the maximum (50%) at (1.4–1.6)R
from the Sun's centre. This decrease can be explained by deflection of the streamers from radial directions. 相似文献
160.