全文获取类型
收费全文 | 74848篇 |
免费 | 1582篇 |
国内免费 | 746篇 |
专业分类
测绘学 | 1850篇 |
大气科学 | 5422篇 |
地球物理 | 15349篇 |
地质学 | 26882篇 |
海洋学 | 6335篇 |
天文学 | 16797篇 |
综合类 | 286篇 |
自然地理 | 4255篇 |
出版年
2022年 | 437篇 |
2021年 | 779篇 |
2020年 | 832篇 |
2019年 | 864篇 |
2018年 | 2022篇 |
2017年 | 1880篇 |
2016年 | 2419篇 |
2015年 | 1445篇 |
2014年 | 2366篇 |
2013年 | 4003篇 |
2012年 | 2476篇 |
2011年 | 3279篇 |
2010年 | 2799篇 |
2009年 | 3711篇 |
2008年 | 3406篇 |
2007年 | 3173篇 |
2006年 | 2977篇 |
2005年 | 2452篇 |
2004年 | 2332篇 |
2003年 | 2177篇 |
2002年 | 1997篇 |
2001年 | 1870篇 |
2000年 | 1773篇 |
1999年 | 1433篇 |
1998年 | 1539篇 |
1997年 | 1429篇 |
1996年 | 1165篇 |
1995年 | 1191篇 |
1994年 | 1006篇 |
1993年 | 917篇 |
1992年 | 882篇 |
1991年 | 783篇 |
1990年 | 894篇 |
1989年 | 753篇 |
1988年 | 675篇 |
1987年 | 853篇 |
1986年 | 696篇 |
1985年 | 886篇 |
1984年 | 959篇 |
1983年 | 916篇 |
1982年 | 864篇 |
1981年 | 738篇 |
1980年 | 692篇 |
1979年 | 644篇 |
1978年 | 635篇 |
1977年 | 583篇 |
1976年 | 557篇 |
1975年 | 523篇 |
1974年 | 531篇 |
1973年 | 495篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
E. M. Drobyshevski 《Earth, Moon, and Planets》1980,23(4):483-491
The hypothesis considering the Jupiter-Sun system as a limiting case of a close binary star implies the initial relative ice abundances in all the Galilean satellites to be essentially equal. The satellites move in the Jovian magnetosphere; thus the unipolar current flowing through their bodies subjected their ices to volumetric electrolysis. Explosions of the electrolysis products resulted in a loss of ices. While Callisto did not explode at all, Ganymede exploded once, Europa twice, and Io two or three times. An analysis of the magnetic field changes needed to create the modern ice abundances in the satellite shows:
- the initial field of Jupiter was ~102 times stronger when compared with the present-day field, and
- the field had to decrease exponentially with τ2| ≈ (0.6?1), which means its relic nature.
992.
Gentileschi ML 《Rivista geografica italiana》1980,87(1):61-74
The author reviews a selection of studies on the behavioral aspects of migration, with emphasis on the process leading up to the decision to migrate. The focus of this review is not on the short-term factors leading to the actual migration decision but on the background factors that lead to the contemplation of migration. The perception by potential migrants of the environment in which they are living as opposed to that of the place to which they might move is considered. (summary in ENG, GER) 相似文献
993.
In the first part, the authors review a group of studies dealing with the identification of regional differences in Italian migratory patterns, especially using the concept of migration field. The second part is devoted to a study of the hierarchical clustering of Italian provinces using 1973 inter-provincial migratory flow data. (summary in ENG, FRE) 相似文献
994.
995.
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
996.
M. E. Bailey 《Astrophysics and Space Science》1977,50(1):3-22
The arguments used by Lyttleton to prove the nonexistence of the Oort cloud are reviewed, and it is shown that Oort's hypothesis remains consistent with observation. The 1950 model of the cloud cannot be correct and, by use of the results from a number of more recent papers, an improved model is described and compared with observations. It is emphasized that comparison of the predictions of theory with observations should concentrate on thea-distribution, as the 1/a-distribution masks much of the detailed structure of the theory. An order of magnitude argument is given which shows that 20% of so-called new comets have passed through the planetary system before, and the implications of this to the statistics of near-parabolic comet orbits are briefly investigated. 相似文献
997.
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
998.
E. M. Drobyshevski 《Solar physics》1977,51(2):473-479
A new mechanism for sustaining enhanced rotational velocity of the outer layers of the solar convective envelope is considered.The gas density inside turbulent eddies decreases because of centrifugal scattering of matter. The decrease of density in eddies rotating in the same sense as the Sun on the whole is larger than that in eddies rotating in the opposite sense. As a result, the former ascend while the latter sink down, thus producing a continuous outward flux of angular momentum.A distribution of angular velocity in the radius of the solar convective envelope in the equatorial plane was obtained in the approximation of the mixing length theory of thermal convection. The results agree rather well with observations. 相似文献
999.
M. N. Gnevyshev 《Solar physics》1977,51(1):175-183
Investigation of sunspots, coronal lines intensity, flares and other solar and geophysical data have confirmed the fact that the 11-year cycle consists of two events (maxima) having different features.During the first maximum (it coincides in time with the maximum of the Wolf numbers) the solar activity increases in all heliographic latitudes but it is maximal in latitude 25° in each hemisphere. The far UV radiation and number of small spots, flares and geomagnetic disturbances with sudden commencements and without 27-day recurrences are maximum at this time.During the second maximum, which appears 2–3 years after the first one, the activity is maximal in latitudes ± 10°. At this time the biggest spots, big flares, aurora and geomagnetic disturbances with the gradual commencements and long series of 27-day recurrences appear.The variations of averaged 5303 and 6374 Å coronal line intensities may be interpreted as an increase of coronal density and temperature during the first maximum and a sharp decrease of density and temperature rise during the second one. The temperature during the second maximum is higher than that during the first one.The distribution of activity on time-latitude diagrams (so-called butterflies) is a result of superposition of two random distributions corresponding to the two maxima mentioned above. 相似文献
1000.
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