全文获取类型
收费全文 | 101173篇 |
免费 | 1725篇 |
国内免费 | 804篇 |
专业分类
测绘学 | 2179篇 |
大气科学 | 6680篇 |
地球物理 | 19367篇 |
地质学 | 36643篇 |
海洋学 | 9356篇 |
天文学 | 23635篇 |
综合类 | 271篇 |
自然地理 | 5571篇 |
出版年
2022年 | 723篇 |
2021年 | 1214篇 |
2020年 | 1339篇 |
2019年 | 1459篇 |
2018年 | 2992篇 |
2017年 | 2790篇 |
2016年 | 3256篇 |
2015年 | 1672篇 |
2014年 | 3129篇 |
2013年 | 5401篇 |
2012年 | 3394篇 |
2011年 | 4394篇 |
2010年 | 3974篇 |
2009年 | 5016篇 |
2008年 | 4390篇 |
2007年 | 4488篇 |
2006年 | 4176篇 |
2005年 | 2962篇 |
2004年 | 2868篇 |
2003年 | 2684篇 |
2002年 | 2664篇 |
2001年 | 2328篇 |
2000年 | 2275篇 |
1999年 | 1818篇 |
1998年 | 1891篇 |
1997年 | 1749篇 |
1996年 | 1497篇 |
1995年 | 1483篇 |
1994年 | 1313篇 |
1993年 | 1201篇 |
1992年 | 1136篇 |
1991年 | 1158篇 |
1990年 | 1161篇 |
1989年 | 982篇 |
1988年 | 923篇 |
1987年 | 1095篇 |
1986年 | 929篇 |
1985年 | 1184篇 |
1984年 | 1283篇 |
1983年 | 1231篇 |
1982年 | 1142篇 |
1981年 | 1040篇 |
1980年 | 976篇 |
1979年 | 890篇 |
1978年 | 886篇 |
1977年 | 746篇 |
1976年 | 753篇 |
1975年 | 730篇 |
1974年 | 709篇 |
1973年 | 785篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
691.
A. Čadež 《Astrophysics and Space Science》1985,109(2):399-402
We respond to comments made in a recent letter by Karimet al. (1984), and show that the examples of interstellar absorption at2800 Å that they have presented so far can all be attributed to overexposure of the IUE detectors. 相似文献
692.
I. A. Issa 《Astrophysics and Space Science》1985,113(2):317-323
The size distribution of dark clouds and of H II regions were used to derive a distance of 440±22 kpc for M31. Some galactic H II regions and dark clouds were combined with the same ingredients in M31 to study the mass spectrum of both phenomena. A gas to dust ratio of 10001 has been derived for M31. Radii of the classical H II regions as derived in this work using distance of 440 kpc agrees with the galactic classical H II region radii. 相似文献
693.
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
694.
S. N. Osipov 《Solar physics》1985,102(1-2):29-32
The blanketing effect for the solar disc center and its value near the limb (cos = 0.23) are obtained for the rocket ultraviolet region using the Harvard center and limb spectra. The value of for the disc center appears to be 0.67 (on average) relative to the quasicontinuum. The essential decrease of towards the limb is also revealed. 相似文献
695.
R. A. Serafin 《Celestial Mechanics and Dynamical Astronomy》1985,36(3):273-280
We consider the collision probability for comets with the Sun under the suppositions of different velocity distributions and various initial conditions. We solve the problem applying Laplace's method and using Schiaparelli's hyperboloid of visibility. The probabilities obtained in this manner are given separately for elliptic and hyperbolic orbits. 相似文献
696.
C. Baixeras M. Casas F. Fernandez A. Vidal-Quadras M. Ortega 《Astrophysics and Space Science》1983,96(2):321-331
Elemental abundances of the VH group of cosmic radiation have been measured in the energy interval 250–550 MeV nucl–1 in a balloon exposure at Sioux Falls (South Dakota) of a plastic detector LeXAN stack. The so obtained abundances have been extrapolated to the sources in the frame of the homogeneous model correcting for energy loss. After taking into account solar modulation, the best fit to model values has led to a escape mean free path e = 5E
–0.4 g cm–2, whereE is the energy in GeV nucl–1, forE>1 GeV nucl–1, and a constant e = 5 g cm–2 forE1 GeV nucl–1. When turning to the diffusion model, also including an energy loss term, a diffusion coefficientD=3×1028 cm2 s–1 has been estimated. 相似文献
697.
Angle-averaged partial frequency redistributionR II has been employed in obtaining a simultaneous solution of radiative transfer equation in the comoving frame and the statistical equilibrium equation for a non-LTE two level atom. We have obtained the ratios of population densities of the upper and lower levels of the resonance line of PV by utilizing the data given in Bernacca and Bianchi (1979). Line source functions are also obtained for different types of variations of density and velocity of the expanding gases. We have considered the atmosphere to be 11 times as thick as the stellar radius. The first iteration was started by putting the density of the upper level (N 2) equal to zero. However, the convergent solution shows a substantial increase inN 2 although it is still much less than the equilibrium value. The line source function and the ratio of the densities of the particles in the upper and lower levels fall sharply from a maximum at τ=τmax to minimum at τ=0. We have studied the scattering integral \(\int {_{ - \infty }^{ + \infty } J_x \phi _x } dx\) and found that this quantity also varies quite similar to the ratioN 2/N 1 and the line source functionS L. 相似文献
698.
The effect of the Coriolis force on the Kelvin-Helmholtz instability has been investigated, in which basic velocities of fluid are varying slowly with lateral coordinatey. The problem is solved by J.W.K.B. approximation method. Parabolic and other types of profiles for wide long channel flow have also been studied in detail. 相似文献
699.
G. A. Pellegatti Franco 《Astrophysics and Space Science》1983,96(1):195-203
Analysis of observational data of OB stars show an, excellent agreement of the density distributions in space ?(x, y, z) as well as in velocity space \(\rho (\dot x,\dot y,\dot z)\) with the predictions of the density wave theory, the values for the density and velocity fluctuations are explained only by the non-linear theory. These theoretical calculations predict perturbations greater than ±10 km s?1, consistent with the observations for the velocity field. Thus one should disregard analytical treatments of the linearized equations since they predict maximum perturbations of ±5km s?1. Another consequence of this is the fact that the Gould's Belt is not a local anomaly, but a local feature of the density waves. The analysis of observational data show that the wave pattern is similar to that of the gas and dust. 相似文献
700.
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