首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   37209篇
  免费   256篇
  国内免费   219篇
测绘学   721篇
大气科学   1708篇
地球物理   7062篇
地质学   14654篇
海洋学   3535篇
天文学   8802篇
综合类   99篇
自然地理   1103篇
  2022年   488篇
  2021年   709篇
  2020年   755篇
  2019年   828篇
  2018年   1696篇
  2017年   1547篇
  2016年   1639篇
  2015年   616篇
  2014年   1415篇
  2013年   2035篇
  2012年   1623篇
  2011年   1898篇
  2010年   1792篇
  2009年   1992篇
  2008年   1769篇
  2007年   1982篇
  2006年   1737篇
  2005年   899篇
  2004年   818篇
  2003年   808篇
  2002年   742篇
  2001年   764篇
  2000年   632篇
  1999年   418篇
  1998年   439篇
  1997年   475篇
  1996年   338篇
  1995年   359篇
  1994年   335篇
  1993年   282篇
  1992年   284篇
  1991年   290篇
  1990年   337篇
  1989年   272篇
  1988年   258篇
  1987年   261篇
  1986年   191篇
  1985年   301篇
  1984年   303篇
  1983年   295篇
  1982年   276篇
  1981年   249篇
  1980年   267篇
  1979年   206篇
  1978年   243篇
  1977年   205篇
  1976年   177篇
  1975年   184篇
  1974年   171篇
  1973年   206篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
281.
We have identified 20 of the 75 unidentified Equatorial Infrared Catalogue Number-1 sources with stars in the BD Catalogue. Two of these are also found in the HD Catalogue.  相似文献   
282.
283.
Transformations are given which change the perturbed planar problem of two bodies into unperturbed and undamped harmonic oscillators with constant coefficients. The orginally singular, nonlinear and Lyapunov unstable equations become in this way regular, linear, and the stable solution may be written down immediately in terms of the new variables. Transformations of the independent and dependent variables are treated separately as well as jointly. Using arbitrary and special functions for the transformations allows a systematic discussion of previously introduced and new anomalies. For the unperturbed two-body problem the theorem is proved according to which if the transformations are power-functions of the radial variable, then only the eccentric and the true anomalies with the corresponding transformations of the radial variable will result in harmonic oscillators. Important practical applications are to increase autonomous operations in space, since by replacing lengthy numerical integrations by transformations, computer requirements are significantly reduced.  相似文献   
284.
Byurakan Astrophysical Observatory; SKB Granit; Geneva Observatory; Flight Control Center. Translated from Astrofizika, Vol. 32, No. 1, p. 5–13, January–February, 1990.  相似文献   
285.
Zakharov's equation is applied to study numerically the evolution of wave amplitudes. It is demonstrated that, owing to Krasitskii's new kernel functions, the system of surface waves remains Hamiltonian, in contrast to the former approaches used by Yuen, Lake, and Zakharov. If surface waves are wind-generated, they grow and become stochastic. If the effect of the waves on the wind is considered, then the wave amplitude evolution, similar to the no-wind case, continues to be recurrent. Translated by Vladimir A. Puchkin.  相似文献   
286.
The results of photometric and polarimetric observations of the star Μ Cep at Byurakan Observatory are presented. Some interesting correlations between the parameters of the star’s brightness variation and the degree of polarization of the light are obtained. It is suggested that the recorded rapid changes in the degree of polarization may result from Μ Cep being a double star. Translated from Astrofizika, Vol. 43, No. 2, pp. 219-228, April–June, 2000.  相似文献   
287.
Based on CCD spectra obtained with the PFES echelle spectrometer of the 6-m telescope, we have determined for the first time the effective temperature T eff=5900 K, surface gravity logg=0.0, and detailed chemical composition of the faint star identified with the infrared source IRAS 23304+6147 by the model-atmosphere method. Its metallicity indicates that the object belongs to the old Galactic disk (the mean abundance of the iron-group elements V, Cr, and Fe for IRAS 23304+6147 is [X/H]=?0.61 dex). The stellar atmosphere exhibits an enhancement of carbon and nitrogen, [C/Fe]=+0.98, [N/Fe]=+1.36, and C/O>1. Significant overabundances of lanthanides were detected: the mean [X/Fe]=+1.04 for La, Ce, Pr, Nd, and Eu. The elemental abundances suggest that the atmospheric chemical composition of IRAS 23304+6147 was modified mainly by nucleosynthesis followed by mixing. By modeling the object's spectrum, we revealed absorption features at the positions of well-known absorption diffuse interstellar bands (DIBs). An analysis of radial-velocity and intensity measurements for these DIBs leads us to conclude that, for IRAS 23304+6147, the DIBs originate mostly in its circumstellar dust envelope expanding at a velocity of about 20 km s?1. Molecular C2 Swan emission bands were detected in the object's spectrum, which also originate in the circumstellar envelope. There is a close match between the object's atmospheric effective temperatures determined independently by the model-atmosphere method and by modeling its optical and infrared energy distribution, within the accuracy of the methods.  相似文献   
288.
We analyze the randomness of the sky distribution of cosmic gamma-ray bursts. These events are associated with massive galaxies, spiral or elliptical, and therefore their positions should trace the large-scale structure, which, in turn, could show up in the sky distribution of fluctuations of the cosmicmicrowave background (CMB). We test this hypothesis by mosaic correlation mapping of the distributions of CMB peaks and burst positions, find the distribution of these two signals to be correlated, and interpret this correlation as a possible systematic effect.  相似文献   
289.
Detailed photometrical monitoring of the cataclysmic variable SDSS J080434.20+510349.2 began at the Crimean Astrophysical Observatory (Ukraine) and the Apache Point Observatory (United States) before the 2006 outburst, continued during the outburst, as well as the following two years. We established the unique nature of the primary and secondary components of the binary. We performed a comprehensive study of the white dwarf’s pulsations over the course of five months, two years after the 2006 outburst. It is shown that the most stable pulsations are equal to or double a period of 12.6 min. On the basis of all the available observations, more precise values for the orbital and the superhump periods were found to be 0.0590048(3) days and 0.059729(4) days, respectively. Our estimation of the mass of the secondary component lies in the range of solar mass from 0.037 to 0.087. This confirms the previous suggestion that the secondary component is most probably a brown dwarf.  相似文献   
290.
Zirker  J. B.  Leroy  J.-L.  Gaizauskas  V. 《Solar physics》1997,176(2):279-283
Leroy, Bommier, and Sahal-Bréchot (1984) determined the vector magnetic field in a large sample of quiescent prominences. The direction of the axial component is in general subject to a 180 deg uncertainty. We have selected those prominences in the sample whose field direction is unambiguous. For 95 such prominences, only 3 do not obey the hemispheric preferences of sinistral or dextral filaments, discovered by Martin, Tracadas, and Billamoria (1994). No explanation for the exceptional cases was found.A search of the Ottawa River Solar Observatory archives was made to check on the structural signatures of sinistral and dextral filaments. Of 32 filaments in common with the Leroy data set, 12 were classifiable as sinistral or dextral from their H fine structure and of these, 3 were exceptions to the hemispheric rule.Thus only a small percentage of quiescent filaments disobeys the hemispheric rule.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号