全文获取类型
收费全文 | 94953篇 |
免费 | 1823篇 |
国内免费 | 760篇 |
专业分类
测绘学 | 2386篇 |
大气科学 | 7196篇 |
地球物理 | 19447篇 |
地质学 | 31882篇 |
海洋学 | 8508篇 |
天文学 | 21368篇 |
综合类 | 195篇 |
自然地理 | 6554篇 |
出版年
2021年 | 685篇 |
2020年 | 811篇 |
2019年 | 868篇 |
2018年 | 1696篇 |
2017年 | 1610篇 |
2016年 | 2199篇 |
2015年 | 1444篇 |
2014年 | 2173篇 |
2013年 | 4735篇 |
2012年 | 2335篇 |
2011年 | 3424篇 |
2010年 | 3043篇 |
2009年 | 4267篇 |
2008年 | 3775篇 |
2007年 | 3607篇 |
2006年 | 3502篇 |
2005年 | 2986篇 |
2004年 | 3030篇 |
2003年 | 2858篇 |
2002年 | 2756篇 |
2001年 | 2437篇 |
2000年 | 2364篇 |
1999年 | 2007篇 |
1998年 | 2018篇 |
1997年 | 2000篇 |
1996年 | 1738篇 |
1995年 | 1648篇 |
1994年 | 1495篇 |
1993年 | 1366篇 |
1992年 | 1303篇 |
1991年 | 1154篇 |
1990年 | 1355篇 |
1989年 | 1194篇 |
1988年 | 1100篇 |
1987年 | 1295篇 |
1986年 | 1181篇 |
1985年 | 1436篇 |
1984年 | 1625篇 |
1983年 | 1523篇 |
1982年 | 1403篇 |
1981年 | 1396篇 |
1980年 | 1171篇 |
1979年 | 1150篇 |
1978年 | 1165篇 |
1977年 | 1100篇 |
1976年 | 1009篇 |
1975年 | 963篇 |
1974年 | 962篇 |
1973年 | 974篇 |
1972年 | 600篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
441.
Tepev Mons is a large volcanic structure of about 250 km in diameter with an elevation of 5 km above the surroundings, located at the southwestern edge of Bell Regio. It is surrounded by a moat with a depth of about 0.5 km. If this moat is considered to be caused by bending of the lithosphere due to the load of the volcano, then elastic bending models give limits for the effective flexural rigidity FR and the effective elastic thickness of the lithosphere L: 2 x 1023 Nm FR 3 x 1024 Nm and 30 km L 100 km. High flexural rigidities are associated with small depressions and large thicknesses of the lithosphere and vice versa.Contribution No 345, Institut für Geophysik der Universität Kiel, F.R.G. 相似文献
442.
The similarity in properties of GK Per and BV Cen suggests that the latter may be a classical nova remnant rather than a dwarf nova. Our H and V CCD photometry show no sign of a nova shell but disclose the presence of a close and probably physical companion. BV(RI)
c
CCD photometry of the companion, assumed to be a dwarf, givesM
v
=3.1±0.3 for BV Cen at quiescence. Even though half of the light in BV Cen comes from the secondary this is much brighter than expected for a dwarf nova and supports the conclusion that BV Cen was an unrecorded nova. 相似文献
443.
An analysis of the effects of the mass transfer on the unsteady free-convection flow of a viscous incompressible fluid, past an impulsively started infinite porous vertical limiting surface with heat sources is presented, when the free-stream velocity and the suction velocity, are oscillating in the time about constant mean values. Approximate solutions for the coupled nonlinear equations are derived for the mean velocity, the mean temperature, the mean skin-friction, and the mean rate of heat transfer. All the above quantities are shown graphically followed, by a discussion. 相似文献
444.
The published photometric and spectroscopic data of the symbiotic binary V 1329 Cyg are interpreted. It is shown, that V 1329 Cyg is an eclipsing binary with an elliptical orbit orbit (e=0.28). The cooler component fills up the Roche-lobe at periastron. A model of moving gaseous structures in the system is proposed and their influence on the radial velocity curve is shown. The following characteristics of the system are derived: the cooler component is an M6 giant with mass 7.9M
, radius 339R
and luminosityM
bol=–5.42, the hot component is a white dwarf surrounded by an accretion disk. The mean distance between the components is 842R
and in periastron it decreases to 605R
. 相似文献
445.
The bump in the ultraviolet part of the interstellar extinction curve provides a great challenge in the modelling of interstellar dust. Its shape can be well approximated by a classical dispersion profile with a total halfwidth of 48 nm centred at 217 nm. Apart from few slightly deviating cases the parameters of the band seem to be surprisingly constant in the solar neighbourhood.The equivalent widthW of the 217 nm band shows a very tight correlation with the colour excessE(B-V). Studies of correlations with the strength of diffuse interstellar bands gave no conclusive results as to the nature of the band.The most common interpretation of the 217 nm feature as originating from small graphite grians meets several difficulties. No final decision on the carrier can be made at present.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986. 相似文献
446.
S. Yabushita K. Wada T. Takai T. Inagaki D. Young E. T. Arakawa 《Astrophysics and Space Science》1986,124(2):377-388
The microorganism model of interstellar grains is investigated by spectroscopy from the infrared (IR), visible to the ultraviolet (UV) wave regions.E. coli, yeast and spores ofBacillus subtilis exhibit absorption bands at =3.1 and 9.7 m; they also exhibit several absorptions at 68 m which are in agreement with the observed IS extinction curves.To obtain the extinction curves in the visible and UV regions, dry films of microorganism are prepared on a MgF2 plate or synthesized quartz plate and their spectra measured. In the wavelength region 190400 nm, conventional spectrophotometers are adopted for the measurement. The extinction curve of the film ofE. coli is similar to the observed IS curve.For the wave-range 100<<400 nm, a vacuum UV spectrometer is adopted to avoid absorptions due to O2 in the atmosphere. The extinction spectra by this method are in agreement with the result obtained by the conventional method where comparison is possible. The extinction curves ofE. coli and yeast are such that they incrase towards the short wavelength and exhibit a peak at -190 nm, which is different from the well-known IS peak at =220 nm. It remains to be seen whether interstellar low temperatures (1040 K) can shift the peak position in the extinction curve of biochemical materials. 相似文献
447.
D. Lorenz-Petzold 《Astrophysics and Space Science》1986,127(2):377-379
It is shown that the recent new Bianchi type-II solutions of Hajj-Boutros (1986a, b) do not exist. We present a consistent method for perfect fluid solutions in this paper. 相似文献
448.
D. Vandev K. Danov P. Mateev P. Petrov M. Kartalev N. Trendafilov Z. K. Smith M. Dryer 《Astrophysics and Space Science》1986,120(2):211-221
A study is presented of an algorithm, based on the statistical analysis of interplanetary magnetic field data, for the real-time detection of discontinuities in the solar wind. The analysis is based on the application of a sliding or searching algorithm together with a minimum variance treatment. A demonstration is given for a Pioneer data set from 29 August, 1966. This particular data set was chosen because it has been extensively studied (in terms of the fast forward MHD shock wave) by previous groups who utilized the three-dimensional Rankine-Hugoniot shock equations after identifying the shock on a subjective basis. Our procedure differs in that it is perfectly objective because of its searching technique. For this particular data set we identify the original shock with excellent agreement with the earlier studies of its normal vector, as well as an additional shock and tangential discontinuity, neither of which had been identified previously. 相似文献
449.
H. J. Staude 《Astrophysics and Space Science》1986,128(1):179-197
The topic is reviewed with emphasis on observations in the optical and near infrared spectral range.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986. 相似文献
450.
We have investigated the evolutionary behaviour of intermediate mass (2, 3, 4, 5, and 7M
) Population I stars, assuming two different rates of rotation at the threshold of stability.In the first part of the study, stars are assumed to start with a critical rotation (fast rotation model) and to progress to the point of rotational instability. The stars evolve by losing mass and become rotationally unstable before they reach the zero-age Main Sequence. It is argued that multiple star systems might be formed through the evolution of rapidly rotating stars. An expression for the rotational mass loss rate is derived as a function of the physical parameters of stars.In the second part of the study, stars are assumed to rotate at a rate below the critical value (slow rotation model). The evolution of slowly rotating stars is followed as far as zero-age Main Sequence on the theoretical Hertzsprung-Russell diagram and compared with that of normal stars. The evolutionary paths are found to be more or less similar to those of normal stars; but their positions on the Main Sequence are characterized by effective temperatures and luminosities lower than those of normal stars. The zero-age Main-Sequence times of these stars are longer than those of normal stars. The rotational rates obtained for the zero-age Main Sequence are in good agreement with observed values. 相似文献