全文获取类型
收费全文 | 85871篇 |
免费 | 989篇 |
国内免费 | 825篇 |
专业分类
测绘学 | 2121篇 |
大气科学 | 5691篇 |
地球物理 | 16207篇 |
地质学 | 33234篇 |
海洋学 | 7424篇 |
天文学 | 18813篇 |
综合类 | 345篇 |
自然地理 | 3850篇 |
出版年
2022年 | 566篇 |
2021年 | 894篇 |
2020年 | 991篇 |
2019年 | 1065篇 |
2018年 | 4245篇 |
2017年 | 3843篇 |
2016年 | 3470篇 |
2015年 | 1290篇 |
2014年 | 2208篇 |
2013年 | 3809篇 |
2012年 | 3198篇 |
2011年 | 5027篇 |
2010年 | 4399篇 |
2009年 | 5251篇 |
2008年 | 4496篇 |
2007年 | 5023篇 |
2006年 | 3045篇 |
2005年 | 2302篇 |
2004年 | 2145篇 |
2003年 | 2159篇 |
2002年 | 1948篇 |
2001年 | 1675篇 |
2000年 | 1569篇 |
1999年 | 1267篇 |
1998年 | 1206篇 |
1997年 | 1243篇 |
1996年 | 1021篇 |
1995年 | 961篇 |
1994年 | 858篇 |
1993年 | 760篇 |
1992年 | 770篇 |
1991年 | 746篇 |
1990年 | 785篇 |
1989年 | 674篇 |
1988年 | 643篇 |
1987年 | 684篇 |
1986年 | 612篇 |
1985年 | 807篇 |
1984年 | 867篇 |
1983年 | 829篇 |
1982年 | 772篇 |
1981年 | 708篇 |
1980年 | 688篇 |
1979年 | 587篇 |
1978年 | 636篇 |
1977年 | 546篇 |
1976年 | 496篇 |
1975年 | 502篇 |
1974年 | 496篇 |
1973年 | 521篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
311.
The solar causes of geomagnetic disturbances 总被引:1,自引:0,他引:1
Geomagnetic disturbances have been identified with respect to their sources for 1977–1983. The disturbance level was found using the daily planetary index A
p. High-amplitude ( 50), mean-amplitude (24) and low-amplitude ( 12) disturbances are caused by solar flares of importance 1, coronal holes, and filament cavities, respectively. The ranges of probable amplitudes of disturbances of different nature and their relative number are found from Poisson random distributions of amplitudes. 相似文献
312.
High-velocity impacts of interplanetary meteoroids on Saturn's rings are discussed. It is shown that the neutral gas emitted by impact vaporization may be responsible, to a large part, for the observed neutral ring atmosphere. Both the predicted neutral gas injection rate and the gas temperature (or kinetic energy) are compatible with the measurements (see Broadfoot, A. L., B. R. Sandel, D. E. Shemansky, J. B. Holberg, G. R. Smith, D. F. Strobel, J. C. McConnell, S. Kumar, D. M. Hunten, S. K. Atreya, T. M. Dohnahne, H. W. Moos, J. L. Bertaux, J. E. Blamont, R. B. Pomphrey, and S. Linik, Science212, 206–211, 1981). Heavy ejecta particles produce a particulate ring “halo”. The physical properties of this halo are calculated, and it appears to be identical with the tenous particle population discussed by Baum and Kreidl (1982). Erosion of Saturn's ring particles, the resulting mass balance, and regolith formation are estimated. This provides some constraints on surface properties and optical albedo. 相似文献
313.
Exact solutions have been obtained for a massive fluid sphere under the extreme causality condition (dP/dρ)=1. Radial pulsational stability of these structures has been discussed. It is found that for pulsationally stable configurations the surface to central density ratio is greater than 0.30, the maximum values for surface and central redshifts are 0.85 and 3.40 respectively in the extreme case, and the maximum mass and size are respectively 4.8M ⊙ and 20.1 km. It has also been shown that these structures are gravitationally bound, with a maximum binding energy per unit rest mass equal to 0.25 for a surface to central density ratio ?0.40. Slow rotation of these configurations has also been considered, and the relative drag and moment of inertia have been calculated. These results have been applied to the Crab pulsar and the mass of the pulsar has also been calculated based upon this model. 相似文献
314.
It is shown that emission lines, first of all the ultraviolet resonance doublet 2800 Mgii, can be used to decipher the internal dynamic structure of QSOs and active galactic nuclei. The electron temperatures of the emission regions of these objects are determined. A hypothesis is proposed explaining the observed broad profiles of the 2800 Mgii line as a summary effect of emission clouds with a Maxwellian velocity distribution. The main physical parameters of emission clouds in QSOs are obtained. A mechanism of formation of emission clouds is suggested: namely, tidal disruption of stars near to a massive compact object. 相似文献
315.
We establish limits on the total radiant energy of solar flares during the period 1980 February – November, using the solar-constant monitor (ACRIM) on board the Solar Maximum Mission. Typical limits amount to 6 × 1029 erg/s for a 32-second integration time, with 5σ statistical significance, for an impulsive emission; for a gradual component, about 4 × 1032 ergs total radiant energy. The limits lie about an order of magnitude higher than the total radiant energy estimated from the various known emission components, suggesting that no heretofore unknown dominant component of flare radiation exists. 相似文献
316.
It is proposed that the solar flare phenomenon can be understood as a manifestation of the electrodynamic coupling process of the photosphere-chromosphere-corona system as a whole. The system is coupled by electric currents, flowing along (both upward and downward) and across the magnetic field lines, powered by the dynamo process driven by the neutral wind in the photosphere and the lower chromosphere. A self-consistent formulation of the proposed coupling system is given. It is shown in particular that the coupling system can generate and dissipate the power of 1029 erg s#X2212;1 and the total energy of 1032 erg during a typical life time (103 s) of solar flares. The energy consumptions include Joule heat production, acceleration of current-carrying particles along field lines, magnetic energy storage and kinetic energy of plasma convection. The particle acceleration arises from the development of field-aligned potential drops of 10–150 kV due to the loss-cone constriction effect along the upward field-aligned currents, causing optical, X-ray and radio emissions. The total number of precipitating electrons during a flare is shown to be of order 1037–1038. 相似文献
317.
The data such as the H-spectrum-spectroheliographic (SSHG) observations, the H-chromospheric observations, etc., of a flare loop prominence which occurred on the western solar limb on 1981 April 27 have been obtained at Yunnan Observatory. The distribution of the internal motions and the macroscopical motion of the flare loop prominence with time and space in the course of its eruption and ascension is derived from the comprehensive analysis of the data. The possible physical pictures and the instability of the motions of the loop are inferred and discussed. 相似文献
318.
The Culgoora radioheliograph has been modified for observing at 327.4 MHz, which is in addition to the three frequencies (43.25, 80, and 160 MHz) previously available. At the new frequency the array beamwidth is 56, which represents the highest resolution yet available for metre-wavelength solar mapping.At 327.4 MHz the sources of radio emission are mainly in the lowest layers of the corona. Some preliminary four-frequency observations have been made of type I storms. It is found that the source size generally decreases with increasing observing frequency. This result confirms earlier suggestions that the sources of both type I and type III emission are contained in structures whose boundaries diverge outwards in the corona. 相似文献
319.
P. Farinella A. Milani A. M. Nobili P. Paolicchi V. Zappala' 《Earth, Moon, and Planets》1983,28(3):251-258
In the set of small satellites of Saturn recently imaged by the Voyager probes, we can observe the transition from irregularly-shaped, strength-dominated objects to larger, gravity-dominated bodies with shapes roughly fitting the theoretical equilibrium figures. The transition occurs for a radius of 100±50 km, corresponding to a typical material strength of the order of 107 dynes cm?2. We discuss briefly the cases of Mimas, Enceladus, Hyperion, Phoebe and the small coorbital and F-ring shepherding moons, showing that an analysis of the shape data can often provide interesting results on the physical properties, origin and collisional history of these objects. 相似文献
320.
V. N. Korzhnev 《Lithology and Mineral Resources》2008,43(6):596-602
In the Ordovician time, the transform margin of the Gornyi Altai region consisted of two bathymetric stages: (1) shelf and upper parts of continental slope; (2) foothills and lower parts of continental slope. The first stage includes the shallow-water facies complexes (terrigenous and terrigenous-carbonate schlieren and variegated flyschoid), while the second stage is composed of deep-water (black shale terrigenous) and subflysch gray (carbonate terrigenous) complexes. Model series of the facies complexes established in our work should be taken into account during the geodynamic analysis of fold zones. 相似文献