全文获取类型
收费全文 | 79081篇 |
免费 | 1028篇 |
国内免费 | 747篇 |
专业分类
测绘学 | 2363篇 |
大气科学 | 6329篇 |
地球物理 | 15133篇 |
地质学 | 30730篇 |
海洋学 | 5962篇 |
天文学 | 16335篇 |
综合类 | 331篇 |
自然地理 | 3673篇 |
出版年
2021年 | 398篇 |
2020年 | 430篇 |
2019年 | 509篇 |
2018年 | 3882篇 |
2017年 | 3655篇 |
2016年 | 3016篇 |
2015年 | 1094篇 |
2014年 | 1579篇 |
2013年 | 2941篇 |
2012年 | 2624篇 |
2011年 | 4565篇 |
2010年 | 4162篇 |
2009年 | 4729篇 |
2008年 | 3921篇 |
2007年 | 4389篇 |
2006年 | 2061篇 |
2005年 | 2153篇 |
2004年 | 1934篇 |
2003年 | 1960篇 |
2002年 | 1791篇 |
2001年 | 1430篇 |
2000年 | 1421篇 |
1999年 | 1215篇 |
1998年 | 1142篇 |
1997年 | 1191篇 |
1996年 | 1074篇 |
1995年 | 999篇 |
1994年 | 923篇 |
1993年 | 793篇 |
1992年 | 750篇 |
1991年 | 769篇 |
1990年 | 788篇 |
1989年 | 742篇 |
1988年 | 694篇 |
1987年 | 838篇 |
1986年 | 749篇 |
1985年 | 862篇 |
1984年 | 973篇 |
1983年 | 960篇 |
1982年 | 904篇 |
1981年 | 831篇 |
1980年 | 779篇 |
1979年 | 711篇 |
1978年 | 713篇 |
1977年 | 652篇 |
1976年 | 586篇 |
1975年 | 577篇 |
1974年 | 644篇 |
1973年 | 652篇 |
1972年 | 417篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
Theoretical studies have shown the possibility of high-temperature ('high enthalpy') geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations. 相似文献
162.
Michael Mendillo Johan Warell Sanjay S. Limaye Jeffrey Baumgardner Ann Sprague Jody K. Wilson 《Planetary and Space Science》2001,49(14-15)
We describe and compare two methods of short-exposure, high-definition ground-based imaging of the planet Mercury. Two teams have recorded images of Mercury on different dates, from different locations, and with different observational and data reduction techniques. Both groups have achieved spatial resolutions of <250 km, and the same albedo features and contrast levels appear where the two datasets overlap (longitudes 270–360°). Dark albedo regions appear as mare and correlate well with smooth terrain radar signatures. Bright albedo features agree optically, but less well with radar data. Such confirmations of state-of-the-art optical techniques introduce a new era of ground-based exploration of Mercury's surface and its atmosphere. They offer opportunities for synergistic, cooperative observations before and during the upcoming Messenger and BepiColombo missions to Mercury. 相似文献
163.
A recently developed near infrared high speed photometer intended for lunar oc-cultation studies is described. The primary scientific objective is to reach milli arc second levels of angular resolution so that circumstellar structure of the occulted sources can be resolved. Near infrared sky brightness close to the lunar limb is also studied. Angular diameter derived from the observed occultation of IRC +20169 is presented and system performance discussed. 相似文献
164.
165.
A. R. King K. Schenker U. Kolb M. B. Davies 《Monthly notices of the Royal Astronomical Society》2001,321(2):327-332
We show that the usual picture of supersoft X-ray binary evolution as driven by conservative thermal time-scale mass transfer cannot explain the short orbital periods of RX J0537.7–7034 (3.5 h) and 1E 0035.4–7230 (4.1 h). Non-conservative evolution may produce such periods, but requires very significant mass loss, and is highly constrained. 相似文献
166.
Summary
Atmospheric backscattering from aerosol particulates has been measured over the Atlantic at 10.6 μm wavelength with an airborne,
coherent heterodyne, lidar, and corresponding air mass back trajectories have been calculated. These back trajectories (usually
extended up to 10 days prior to the backscatter measurement) have shown very diverse origins for the air parcels at different
altitudes. In many cases it has been possible to attribute the observed levels of scattering to these origins over oceanic,
arctic, continental, industrial etc. regions. This is illustrated by 6 flight records: out of Ascension Island in the South
Atlantic; over the Azores in the mid North Atlantic; over the UK and the North Sea; and in the Arctic along 71° North. In
each of these regions the profiles of backscatter versus altitude show highly variable features; remarkably different origins
for air masses at different altitudes are evident from the corresponding back trajectory analyses. It is thus possible for
the first time to present probable explanations for the different levels of scattering observed at different altitudes.
Received July 14, 2000 Revised May 14, 2001 相似文献
167.
168.
D. Gerbal H.V. Capelato F. Durret G.B. Lima Neto I. Márquez 《Astrophysics and Space Science》2001,276(2-4):861-868
We suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a specific entropy. We use
the Sérsic law to describe the light profile. The specific entropy (the Boltzmann–Gibbs definition) is then calculated assuming
that the galaxy behaves as a spherical, isotropic, one-component system. We predict a relation between the three parameters
of the Sérsic law linked to the specific entropy, defining a surface in the parameter space, an ‘entropic plane’. We have
analysed a sample of simulated merging elliptical galaxies (virtual) and a sample of galaxies belonging to the Coma Cluster (real). Both virtual and realgalaxies are: 1) located in their own ‘entropic plane‘ and 2) in this plane, they are located on a straight line, indicating
constant entropy: another physical property A careful examination of the value of the specific entropy indicates a very small
increase in the specific entropy with the generation after merging (virtual sample). Although one cannot distinguish between various generations for real galaxies, the distribution of specific entropy in this sample is very similar to that in the virtual sample.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
169.
We present 2-D, fully compressible radiation-MHD simulations of the solar photospheric and subphotospheric layers that run for 2 hours of solar time starting from a magnetic configuration with mixed polarities. In the atmospheric layers the simulation reveals a correlation between field strength and inclination, with a nearly vertical strong-field magnetic component and a more horizontal weak-field component, in agreement with the observations. Our simulation also shows that magnetic flux is converted from one of these states to the other. In particular, magnetic flux sheets can also be formed when a new downflow lane starts due to granule fragmentation. The dynamics of the granulation and field-line reconnection are found to play a role in the initial stages of a magnetic element's formation. The simulation predicts that during or shortly after their formation magnetic elements could be associated with oppositely polarized flux at a small spatial scale. 相似文献
170.
C.J. Mooney W.R.J. Rolleston F.P. Keenan P.L. Dufton D.L. Pollacco H.R. Magee 《Monthly notices of the Royal Astronomical Society》2001,326(3):1101-1109
We present a model-atmosphere analysis for the bright ( V ∼13) star ZNG-1, in the globular cluster M10. From high-resolution ( R ∼40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T eff =26 500±1000 K and log g =3.6±0.2 dex . A differential abundance analysis reveals a chemical composition typical of hot post-AGB objects, with ZNG-1 being generally metal poor, although helium is approximately solar. The most interesting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relative to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar stars suggest that gas–dust fractionation in the AGB progenitor could be responsible for the observed composition of these objects. However, we need not invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metallicity. 相似文献