全文获取类型
收费全文 | 5688篇 |
免费 | 281篇 |
国内免费 | 44篇 |
专业分类
测绘学 | 156篇 |
大气科学 | 393篇 |
地球物理 | 2137篇 |
地质学 | 1865篇 |
海洋学 | 424篇 |
天文学 | 733篇 |
综合类 | 28篇 |
自然地理 | 277篇 |
出版年
2022年 | 39篇 |
2021年 | 112篇 |
2020年 | 113篇 |
2019年 | 80篇 |
2018年 | 231篇 |
2017年 | 221篇 |
2016年 | 340篇 |
2015年 | 258篇 |
2014年 | 288篇 |
2013年 | 374篇 |
2012年 | 312篇 |
2011年 | 322篇 |
2010年 | 267篇 |
2009年 | 292篇 |
2008年 | 244篇 |
2007年 | 216篇 |
2006年 | 173篇 |
2005年 | 150篇 |
2004年 | 172篇 |
2003年 | 126篇 |
2002年 | 85篇 |
2001年 | 99篇 |
2000年 | 75篇 |
1999年 | 66篇 |
1998年 | 85篇 |
1997年 | 72篇 |
1996年 | 49篇 |
1995年 | 41篇 |
1994年 | 59篇 |
1993年 | 43篇 |
1992年 | 47篇 |
1991年 | 39篇 |
1990年 | 57篇 |
1989年 | 41篇 |
1988年 | 33篇 |
1987年 | 35篇 |
1986年 | 41篇 |
1985年 | 28篇 |
1984年 | 42篇 |
1983年 | 37篇 |
1982年 | 40篇 |
1981年 | 28篇 |
1979年 | 27篇 |
1978年 | 32篇 |
1977年 | 30篇 |
1976年 | 28篇 |
1975年 | 31篇 |
1974年 | 35篇 |
1973年 | 34篇 |
1971年 | 41篇 |
排序方式: 共有6013条查询结果,搜索用时 15 毫秒
101.
Ján Boďa 《Studia Geophysica et Geodaetica》1992,36(2):139-150
Summary Our discussion is concerned with the common effect of the non-uniformity of layer rotation and stratification. We have assumed a model of differential rotation with the upper part of the layer rotating more slowly, the bottom part more quickly. The upper part of the layer is stratified stably, the bottom part unstably.The thermal instabilities are preferred in the strong differential rotation case and they are the most easily excited by a strong magnetic field (102–103). The direction of its propagation is westward in the uniformly stratified layer and eastward in the non-uniformly stratified layer. 相似文献
102.
Summary The Banach theorem is applied to the Lagrange planetary equation for the semimajor axis of a geostationary satellite orbit to estimate the stability of near-geostationary satellite orbits. To achieve a graveyard (disposal) orbit, which will not interfere (=cross) the initial geostationary orbit, the geostationary semi-major axis ag have to be increased at least by 50 km. Numerical results for a variety of graveyard orbits show that the increase of ag by about 100 km will yield sufficiently stable orbits (accounting for the Earth's gravitational perturbations only) during the next 150 years.Dedicated to the 75th Birthday of Professor Academician Tibor Kolbenheyer 相似文献
103.
Drahomír Dušátko 《Studia Geophysica et Geodaetica》1992,36(4):392-393
Summary The method of the automated computation of the gravimetric deflections of the vertical and of the geoidal heights for the European region is described. The work was carried out during the period 1986–1988 by the Topographic Service of the Czechoslovak Army. The computation applies to 20 sheets of the international map 1:1 000 000 (total area of =16c, =30c - see Fig. 1). The mean values of the free-air anomalies for each surface element =5, =7.5, approximately 9 × 9 km, were used with radius of integration of 300 km. 相似文献
104.
We study the evolution of solid, CO white dwarfs after explosive carbon ignition at central densities around 1010 g cm–3 triggered by steady accretion in a close binary system, in order to elucidate whether these stars can collapse to form a neutron star. We show that as long as the velocity of the burning front remains below a critical value of 0.006c
s (60 km s–1), gravitational collapse is the final fate. These calculations support the accretion-induced collapse (AIC) scenario for the origin of a fraction of low-mass X-ray binaries.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
105.
In the five last years, different structures (density excess 1) have been proposed as the direct cause of our infall toward the direction of Hydra—Centaurus with a velocity of 500 km s–1. The direct effect of the mentioned matter accumulations on the X-ray background (XRB) can be estimated as a function of the geometry of the structures and of the cosmological evolution of the sources emitting in the X-ray band (2–10 keV) for different universes (01). If the XRB comes mostly from AGNs with low luminosity (L
X
<1043 erg s–1 and, therefore, they will have a weak cosmological evolution) and we consider the difference between the intensities coming from both hemispheres (that oriented toward the direction of our motion and the opposite one) obtained by means of different satellites, we can conclude that some candidates are highly unlikely.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain 相似文献
106.
Periodic orbits in the Stormer problem are studied using the symmetry lines of the Poincaré map introduced by De Vogelaere. Many known facts are explained by mean of these lines. The dynamics of four special symmetry lines when the Stormer parameter 1 changes is presented, and we obtain a clear global view of the structure of the simple periodic orbits and their bifurcations, including the asymmetrical ones. New asymmetrical multiple periodic orbits are obtained. 相似文献
107.
J. Zahradník M. Antonini G. Grünthal J. Janský D. Procházková E. Schmedes A. Špičak J. Zedník 《Pure and Applied Geophysics》1990,133(1):53-71
The main shock of the West-Bohemian earthquake swarm, Czechoslovakia, (magnitudem=4.5, depthh=10 km) exhibits an irregular areal distribution of macroseismic intensities 6° to 7° MSK-64. Four lobes of the 6° isoseismal are found and the maximum observed intensity is located at a distance of 8 km from the instrumentally determined epicentre. This distribution can be explained by the energy flux of the directS wave generated by a circular source, the hypocentral location and focal mechanism of which are taken from independent instrumental studies. The theoretical intensity, which is assumed to be logarithmically proportional to the integrated squared ground-motion velocity (i.e.,I=const+log v
2
(t)dt), fits the observed intensity with an overall root-mean-square error less than 0.5°. It is important that the present intensity data can also be equally well explained by the isotropic source. The fit was attained by means of a horizontally layered model though large fault zones and an extended sedimentary basin suggest a significant lateral heterogeneity of the epicentral region. The results encourage a broader application of the simple modelling technique used. 相似文献
108.
Ignacio Ferrín 《Astrophysics and Space Science》1975,33(2):453-457
An analysis of the Lowell Observatory photographic plates of Saturn gave the following results: (1) ring A and B show peculiar brightness distributions around the planet, from which we conclude that both are composed of particles in synchronous rotation. (2) The leading side of the particles in ring A is brighter than the trailing side by about 4%, which may indicate an interaction between such particles and the interplanetary medium. (3) Scans of the rings across the major axis show a small (~0.3″) region of enhanced brightness, from which we derive a value ofT s =10h13 . m 8±5 . m 4 for the actual planetary rotational period of Saturn. (4) In order to explain the synchronous rotation, the particles in ring A have to be at least 42 m in diameter. 相似文献
109.
110.
Models of factors controlling late Pleistocene pluvial lake-level fluctuations in the Great Basin are evaluated by dating lake levels in Jakes Valley. “Jakes Lake” rose to a highstand at 13,870 ± 50 14C Yr B.P., receded to a stillstand at 12,440 ± 50 14C yr B.P., and receded steadily to desiccation thereafter. The Jakes Lake highstand is roughly coincident with highstands of lakes Bonneville, Lahontan and Russell. The rise to highstand and recession of Jakes Lake were most likely controlled by a storm track steered by the polar jet stream. The final stillstand of Jakes Lake helps constrain timing of northward retreat of the polar jet stream during the Pleistocene-Holocene transition. 相似文献