全文获取类型
收费全文 | 43113篇 |
免费 | 900篇 |
国内免费 | 438篇 |
专业分类
测绘学 | 1019篇 |
大气科学 | 2341篇 |
地球物理 | 9152篇 |
地质学 | 17028篇 |
海洋学 | 3879篇 |
天文学 | 9247篇 |
综合类 | 336篇 |
自然地理 | 1449篇 |
出版年
2022年 | 527篇 |
2021年 | 773篇 |
2020年 | 795篇 |
2019年 | 882篇 |
2018年 | 2160篇 |
2017年 | 1934篇 |
2016年 | 1918篇 |
2015年 | 790篇 |
2014年 | 1575篇 |
2013年 | 2193篇 |
2012年 | 2278篇 |
2011年 | 2346篇 |
2010年 | 1947篇 |
2009年 | 2172篇 |
2008年 | 1921篇 |
2007年 | 2132篇 |
2006年 | 1894篇 |
2005年 | 1728篇 |
2004年 | 1690篇 |
2003年 | 1481篇 |
2002年 | 960篇 |
2001年 | 871篇 |
2000年 | 712篇 |
1999年 | 457篇 |
1998年 | 452篇 |
1997年 | 499篇 |
1996年 | 353篇 |
1995年 | 365篇 |
1994年 | 337篇 |
1993年 | 287篇 |
1992年 | 290篇 |
1991年 | 302篇 |
1990年 | 347篇 |
1989年 | 279篇 |
1988年 | 260篇 |
1987年 | 267篇 |
1986年 | 196篇 |
1985年 | 306篇 |
1984年 | 307篇 |
1983年 | 299篇 |
1982年 | 277篇 |
1981年 | 255篇 |
1980年 | 272篇 |
1979年 | 208篇 |
1978年 | 244篇 |
1977年 | 208篇 |
1976年 | 182篇 |
1975年 | 189篇 |
1974年 | 173篇 |
1973年 | 212篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets. 相似文献
52.
Radio astronomy experiments designed to probe the interplanetary plasma close to the Sun have been carried out at the wavelength = 2.92 m using the occultation method. The experiments are based on a modification of the occultation method by which the sources, in this case quasars, are used to measure the radial dependence of the apparent source size, the scattering angle (R). The radial dependence of this source size (R) reveals that an anomalous enhancement in the scattering appears at radial distances from about 16 to 30 R
, which is associated with the solar wind transsonic region. It is shown by analysis of the theoretical equations that the radial profiles of both the source size (R) and the scintillation index m(R) are consistent in the near solar interplanetary medium (R 40 R
). Combining these two independent applications of the occultation method extends the range of the investigation and provides a powerful new diagnostic of the solar wind transsonic region. 相似文献
53.
Formulae containing the elements of the variational matrix are obtained which determine the linear isoenergetic stability parameters of three-dimensional periodic orbits of the general three-boy problem. This requires the numerical integration of the variational equations but produces the stability parameters with the effective accuracy of the numerical integration. The conditions for stability, criticality, and bifurcations are briefly examined and the stability determination procedure is tested in the determination of some three-dimensional periodic orbits of low inclination bifurcating from vertical-critical coplanar orbits. 相似文献
54.
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
55.
This paper is devoted to Force-Free Electromagnetic Oscillations in a constant magnetic field. A correction is made in the derivation of the basic equation. The paper confirms the predicted spectrum of frequencies, namely
n
=
o
(n + 1)1/2;n = 0, 1, 2, .... In addition it is suggested that hybrid frequency
n
= (
n
2
+
H
2
)1/2 should be found in observational data. 相似文献
56.
The abundances of light elements (deuterium, helium and lithium) are calculated in unconventional cosmologies in which these elements are produced by interaction of fast -particles ejected by massive pregalactic stars with a purely hydrogenous cosmological substrate. The number density and energetics of such stars needed for suitable production of light elements are estimated. It is shown that the models always lead to overproduction of lithium. The intensity of ultraviolet, X-ray, and -ray emission caused by explosions of pregalactic massive stars is calculated. The distortions of cosmic background radiation by Compton losses of electrons heated by explosive stars are also calculated. 相似文献
57.
A simple self-consistent model of a high-temperature turbulent current sheet (HTCS) is considered. The anomalous character of plasma conductivity in a sheet is assumed to be due to gradient instabilities. The possibility of a low threshold of their excitation is demonstrated by an example of temperature-drift instability.Application of the HTCS model to the hot or main phase of a solar flare is discussed. The model consistently explains many observed properties of this phase. 相似文献
58.
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
59.
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
60.