全文获取类型
收费全文 | 188471篇 |
免费 | 13700篇 |
国内免费 | 18314篇 |
专业分类
测绘学 | 11688篇 |
大气科学 | 15560篇 |
地球物理 | 37736篇 |
地质学 | 82561篇 |
海洋学 | 21308篇 |
天文学 | 32271篇 |
综合类 | 4099篇 |
自然地理 | 15262篇 |
出版年
2023年 | 1663篇 |
2022年 | 3681篇 |
2021年 | 5000篇 |
2020年 | 4392篇 |
2019年 | 5022篇 |
2018年 | 6268篇 |
2017年 | 6028篇 |
2016年 | 6826篇 |
2015年 | 5689篇 |
2014年 | 7182篇 |
2013年 | 11154篇 |
2012年 | 8494篇 |
2011年 | 9965篇 |
2010年 | 9103篇 |
2009年 | 10531篇 |
2008年 | 9744篇 |
2007年 | 9460篇 |
2006年 | 9032篇 |
2005年 | 7176篇 |
2004年 | 6409篇 |
2003年 | 5518篇 |
2002年 | 5379篇 |
2001年 | 4748篇 |
2000年 | 4344篇 |
1999年 | 3142篇 |
1998年 | 2991篇 |
1997年 | 2792篇 |
1996年 | 2424篇 |
1995年 | 2380篇 |
1994年 | 2060篇 |
1993年 | 1864篇 |
1992年 | 1824篇 |
1991年 | 1710篇 |
1990年 | 1912篇 |
1989年 | 1652篇 |
1988年 | 1498篇 |
1987年 | 1799篇 |
1986年 | 1585篇 |
1985年 | 1997篇 |
1984年 | 2222篇 |
1983年 | 2087篇 |
1982年 | 1948篇 |
1981年 | 1778篇 |
1980年 | 1627篇 |
1979年 | 1528篇 |
1978年 | 1508篇 |
1977年 | 1430篇 |
1976年 | 1328篇 |
1975年 | 1289篇 |
1973年 | 1343篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
W. R. Dick S. Hirte E. Schilbach R. -D. Scholz 《Astrophysics and Space Science》1991,177(1-2):229-234
The observations and the plate reduction technique for the determination of positions and absolute proper motions which is used in Potsdam are described. Recent results have shown that an accuracy of about 0
.
1 for positions and 0
.
7
cent
.
–1
for proper motions can be achieved both for bright (8m–12m) and faint (16m–18m) stars. Three astrometric programmes using the Tautenburg plates are presented. 相似文献
942.
Charles H. Nelson Douglas S. Hall Francis C. Fekel Robert E. Fried Richard E. Lines Helen C. Lines 《Astrophysics and Space Science》1991,182(1):1-17
Photometry of HD 155638=V792 Her has been analyzed to determine the elements of this totally eclipsing RS CVn binary. The light variation outside eclipse was found to have a period of 27d.07±0d.07, which is slightly different from the 27d.5384±0d.0045 orbital period. Analysis of the eclipses was achieved by a modification of the Russell-Merrill technique. With the aid of radial velocity measures, absolute elements were obtained for the hot and cool stars, respectively;R
h=2.58R
,R
c=12.28R
,M
h=1.40M
,M
c=1.46M
,i=80o.61 and velocity semi-amplitudesK
c=48.36 km s–1±0.79 km s–1, andK
h=50.50 km s–1±0.33 km s–1. The apparent magnitudes areV
h=9
m
.73 andV
c=8
m
.48. The distance to HD 155638 was estimated to be 310 parsecs. 相似文献
943.
The transition from local horizon and terrestrial BIH-systems to celestial reference frames is well known to be affected by various geodetic parameters such as polar motion (xp(t), yp(t)), UT1-TUC (where UT1 is basically dependent on variations in UT0 and t=time), plumb line deflections (, ) of observation stations, global and local tidal deformations etc. Variations of such quantities with (relative) resolution of the order of 0.001 and better, such as VLBI, demand the application of continuous high-precision (world-wide) geodynamic surveys whenever global theories and sufficient models are not available and the introduction of improved local and global models (geophysical and relativistic) is needed in order to match astrometric observations related to different reference frames. Prediction of parameters for immediate transformation from one system of reference into the other is sometimes of interest.The paperreviews recent results of different observations,points out a number of still open and unresolved problems in observations and modeling, anddiscusses related consequences. Conclusions for geodynamics drawn from comparison of observed data with models based on astronomical and geophysical observations give way to new understanding of basic phenomena of relevance for various disciplines. 相似文献
944.
A principally new, quantitative system of the classification of the spectra of planetary nebulae is proposed. Spectral class of excitation class of the nebulap is determined according to the relative intensities of emission lines (N
1+N
2) [OIII]/4686 HeII and (N
1+N
2) [OIII]/H (Table I, Figure 1). The excitation classes are obtained for 142 planetary nebulae of all classes—low (p=1–3), middle (p=4–8), and high (p=9–12+) (Tables II, III, and IV). An empirical relationship between excitation classp and mean radius of nebulae
is discovered (Figure 2). This relationship as well as excitation classp, as an independend parameter, admit an evolutionary interpretation. It is shown that after reaching the highest class of excitationp=12+ the nebulae decrease their class of excitation with the further increases of sizes. The diagram of this relationship
has two nearly-symmetric branches — rising and descending with the apogee onp=12+ (Figure 2). 相似文献
945.
A detailed list of line identifications of the far UV spectrum of the O4I(n)f star Puppis (HD 66811) in the wavelength range 1168–1984 Å recorded on 16 April, 1981 with the International Ultraviolet Explorer (IUE) is presented. The detailed analysis of the radial velocities measured in the same wavelength range is also presented. 相似文献
946.
The variations of the declinations of 36 Belgrade zenith stars from BZS170 Catalogue published in Astronomy and Astrophysics,177, 313–316 (1987) are examined by spectral analysis. The prospect is to evaluate multiples of the Chandler period of which the most prominent for all stars is the double one. 相似文献
947.
G. Z. Xie F. K. Liu Y. Y. Zhu J. H. Fan R. W. Lu 《Astrophysics and Space Science》1991,179(2):321-329
It has become clear in recent years that relativistic beaming is a good explanation for the BL Lac phenomenon. Of studies based on the relativistic beaming model of BL Lac objects, we note that the orientation of jet's axis to the line-of-sight is very small and, therefore, the observed flux emitted from a rapidly moving source is orders of magnitude higher than the flux in its rest-frame:F
obs = 3 +
F
intr, where is the bulk relativistic Doppler factor. Then the observed apparent magnitudem
v
must be corrected for this effect. For our 39 samples, the corrected apparent magnitudem
v
corr
and logZ have a good correlation. 相似文献
948.
E. F. Arias C. Boucher M. Feissel J. -F. Lestrade 《Astrophysics and Space Science》1991,177(1-2):187-192
The relative orientations of various VLBI celestial reference frames are evaluated on the basis of coordinate differences of common sources. It is shown that an accuracy better than 0.001 can be achieved. Possible regional deformations in the different catalogues are investigated; they are found to reach a few 0.001 in some restricted zones. The application of these studies to the realisation of a combined celestial reference frame consistent with the BIH Terrestrial System is outlined. 相似文献
949.
V. G. Surdin 《Astrophysics and Space Science》1991,183(1):129-134
Four pairs of visual double star clusters with the lowest mass-to-luminosity ratio have been selected among globular clusters of our Galaxy. By taking into accounts the effects of dynamical friction and compressive gravitational shocks, we conclude that the probability for the pairs to be gravitationally bound is very low. 相似文献
950.
Glenn M. Frye Jr. Philip P. Dunphy Edward L. Chupp Paul Evenson 《Solar physics》1988,118(1-2):321-346