全文获取类型
收费全文 | 265497篇 |
免费 | 5242篇 |
国内免费 | 3455篇 |
专业分类
测绘学 | 7197篇 |
大气科学 | 19503篇 |
地球物理 | 55795篇 |
地质学 | 93120篇 |
海洋学 | 22073篇 |
天文学 | 57225篇 |
综合类 | 1053篇 |
自然地理 | 18228篇 |
出版年
2021年 | 2253篇 |
2020年 | 2640篇 |
2019年 | 2874篇 |
2018年 | 4412篇 |
2017年 | 4051篇 |
2016年 | 6225篇 |
2015年 | 4283篇 |
2014年 | 6988篇 |
2013年 | 14303篇 |
2012年 | 6867篇 |
2011年 | 8583篇 |
2010年 | 7547篇 |
2009年 | 10154篇 |
2008年 | 8945篇 |
2007年 | 8530篇 |
2006年 | 9768篇 |
2005年 | 7922篇 |
2004年 | 7845篇 |
2003年 | 7314篇 |
2002年 | 6883篇 |
2001年 | 6115篇 |
2000年 | 6009篇 |
1999年 | 5226篇 |
1998年 | 5255篇 |
1997年 | 5069篇 |
1996年 | 4710篇 |
1995年 | 4450篇 |
1994年 | 4132篇 |
1993年 | 3875篇 |
1992年 | 3669篇 |
1991年 | 3618篇 |
1990年 | 3774篇 |
1989年 | 3529篇 |
1988年 | 3314篇 |
1987年 | 3866篇 |
1986年 | 3430篇 |
1985年 | 4248篇 |
1984年 | 4750篇 |
1983年 | 4416篇 |
1982年 | 4326篇 |
1981年 | 3939篇 |
1980年 | 3659篇 |
1979年 | 3515篇 |
1978年 | 3496篇 |
1977年 | 3294篇 |
1976年 | 3062篇 |
1975年 | 2967篇 |
1974年 | 2922篇 |
1973年 | 3090篇 |
1972年 | 2026篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
991.
E. N. Parker 《Solar physics》1985,100(1-2):599-619
The future of solar physics is founded on the existing fundamental unsolved problems in stellar physics. Thus, for instance, the physics of stellar interiors has been called into serious question by the very low-measured neutrino flux. The 71Ga neutrino detection experiment is the next step in unravelling this mystery. If that experiment should find the expected neutrino flux from the basic p-p reaction in the Sun, then astrophysics is in a difficult situation, because the most likely explanation for the low neutrino flux found in the 37Cl experiment would be an error in our calculation of the opacity or an error in our understanding of the elemental abundances in stellar interiors, with serious implications for present ideas on stellar structure and the age of the galaxy.The new methods of helioseismology, for probing the interior of the Sun, have already found the primordial rapid rotation of the central core. The forthcoming world-wide helioseismology observing network will permit fuller exploitation of the method, promising to provide the first direct sounding of the interior of a star, hitherto known to us only through theoretical inference and the discrepant neutrino emission.The activity of all stars involves much the same phenomena as make up the activity of the Sun. The effects are too complex, and too foreign to the familiar dynamics in the terrestrial laboratory, to be deciphered by theoretical effort alone. It has become clear through the observational and theoretical work of the past decade or two that much of the essential dynamics of the activity of the atmosphere takes place on scales of the order of 102 km. Thus, an essential step in developing the physics of stellar activity will be the Solar Optical Telescope (presently planned by NASA to be launched early in the next decade) to permit a microscopic examination of the surface of the Sun to study the source of the action. The activity and X-ray emission of other stars depend on much the same effects, so that the study is essential to determining the significance of the X-ray emission from other stars.This work was supported in part by the National Aeronautics and Space Administration under grant NGL-14-001-001. 相似文献
992.
P. Nenovski 《Planetary and Space Science》1985,33(11):1313-1316
In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky.This characteristic of compressional surface MHD waves is inherent for the spectrum , obtained by Nenovski (1978) in the cold plasma limit VA ? VS(VA is Alfvén velocity, and VS, sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed. 相似文献
993.
Luigi R. Bedin † Santi Cassisi Fiorella Castelli Giampaolo Piotto Jay Anderson Maurizio Salaris Yazan Momany Adriano Pietrinferni 《Monthly notices of the Royal Astronomical Society》2005,357(3):1038-1048
We propose a zero-point photometric calibration of the data from the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) on board the Hubble Space Telescope , based on a spectrum of Vega and the most up-to-date in-flight transmission curves of the camera. This calibration is accurate at the level of a few hundredths of a magnitude. The main purpose of this effort is to transform the entire set of evolutionary models into a simple observational photometric system for ACS/WFC data, and to make them available to the astronomical community. We provide the zero-points for the most used ACS/WFC bands, and give basic recipes for calibrating both the observed data and the models. We also present the colour–magnitude diagram from ACS data of five Galactic globular clusters, spanning the metallicity range −2.2 <[Fe/H] < −0.04 , and we provide fiducial points representing their sequences from several magnitudes below the turn-off to the red giant branch tip. The observed sequences are compared with the models in the newly defined photometric system. 相似文献
994.
995.
David E. Fisher 《Meteoritics & planetary science》1985,20(1):37-41
Uranium was measured by fission track analysis in meteoritic troilite and graphite. The distribution is extremely heterogeneous, with a few high-U grains dominating the total abundances. U/He ages cannot be estimated from such a distribution pattern, and therefore previously reported excessive ages are not valid. 相似文献
996.
An estimate for the anisotropy of the turbulent viscositys is given in a convective layer heated from below and rotating around a vertical axis. In the case of two-dimensional convection,
there is a stationary regime withs⊇2 regardless of the rotation. In the case of three-dimensional convection in a slowly rotating layer (with the Taylor number
equal to 1600), nonstationary turbulent regimes take place withs⊇1.6 forR=2.5×104 (R is the Rayleigh number) ands⊇1.2 forR=104.
The parameters plays an, important role in the theory of differential rotation of the convective solar or stellar envelopes. So far, it
has been evaluated empirically or semi-empirically. Some prospects in the development of the theory of differential rotation
are discussed here in terms of the moment theory of hydrodynamic fields. The relation between this strict approach and an
anisotropic viscosity approximation is considered. 相似文献
997.
998.
999.
Vertical measurements of , and N2O concentrations, and uptake, and oxidation rates were measured at 5 sites in western Cook Strait, New Zealand, between 31 March and 3 April 1983. Nitrate increased with depth at all stations reaching a maximum of 10.5 μg-atom at the most strongly stratified station whereas was relatively constant with depth at all stations (~0.1 μg-atom ). The highest rates of oxidation generally occurred in the near surface waters and decreased with depth. N2O levels were near saturation with respect to the air above the sea surface and showed no obvious changes during 24 h incubation. oxidation by nitrifying bacteria may account for about 30% of the total utilization (i.e. bacterial+agal) and, assuming oxidation through to , may supply about 40% of the algal requirements of in the study area. These results suggest that bacterial nitrification is of potential importance to the nitrogen dynamics of the western Cook Strait, particularly with respect to the nitrogen demands of the phytoplankton. 相似文献
1000.