全文获取类型
收费全文 | 23316篇 |
免费 | 3539篇 |
国内免费 | 3092篇 |
专业分类
测绘学 | 6289篇 |
大气科学 | 2111篇 |
地球物理 | 5759篇 |
地质学 | 7613篇 |
海洋学 | 1559篇 |
天文学 | 2765篇 |
综合类 | 2103篇 |
自然地理 | 1748篇 |
出版年
2024年 | 86篇 |
2023年 | 204篇 |
2022年 | 668篇 |
2021年 | 888篇 |
2020年 | 842篇 |
2019年 | 1052篇 |
2018年 | 748篇 |
2017年 | 1120篇 |
2016年 | 1046篇 |
2015年 | 1047篇 |
2014年 | 1254篇 |
2013年 | 1486篇 |
2012年 | 1403篇 |
2011年 | 1297篇 |
2010年 | 1036篇 |
2009年 | 1432篇 |
2008年 | 1503篇 |
2007年 | 1609篇 |
2006年 | 1586篇 |
2005年 | 1299篇 |
2004年 | 1314篇 |
2003年 | 1036篇 |
2002年 | 889篇 |
2001年 | 808篇 |
2000年 | 738篇 |
1999年 | 604篇 |
1998年 | 542篇 |
1997年 | 377篇 |
1996年 | 361篇 |
1995年 | 323篇 |
1994年 | 297篇 |
1993年 | 257篇 |
1992年 | 185篇 |
1991年 | 123篇 |
1990年 | 94篇 |
1989年 | 100篇 |
1988年 | 71篇 |
1987年 | 53篇 |
1986年 | 27篇 |
1985年 | 23篇 |
1984年 | 15篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 28篇 |
1977年 | 12篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1954年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
Wei-Hao Bian Hong Dong Yong-Heng Zhao National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Physics Nanjing Normal University Nanjing Department of Physics Shangqiu Teachers College Shangqiu 《中国天文和天体物理学报》2004,4(1):61-66
In a previous paper, it was suggested that contamination of the nuclear luminosity by the host galaxy plays an important role in determining the parameters of the standard a disk of AGNs. Using the nuclear absolute B band magnitude instead of the total absolute B band magnitude, we have recalculated the central black hole masses, accretion rates and disk inclinations for 20 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars. It is found that a small value of a is needed for the Seyfert 1 galaxies than for the PG quasars. This difference in a possibly leads to the different properties of Seyfert 1 galaxies and quasars. Furthermore, we find most of the objects in this sample are not accreting at super-Eddington rates if we adopt the nuclear optical luminosity in our calculation. 相似文献
12.
A highly automated moving object detection package 总被引:1,自引:0,他引:1
13.
Cygnus A was the first hyper-active galaxy discovered, and it
remains by far the closest of the ultra-luminous radio galaxies. As
such, Cygnus A has played a fundamental role in the study of virtually
all aspects of extreme activity in galaxies. We present a review of jet
theory for powering the double-lobed radio emitting structures in
powerful radio galaxies, followed by a review of observations of Cygnus
A in the radio, optical, and X-ray relevant to testing various aspects
of jet theory. Issues addressed include: jet structure from pc- to
kpc-scales, jet stability, confinement, composition, and velocity, the
double shock structure for the jet terminus and the origin of multiple
radio hotspots, the nature of the filamentary structure in the radio
lobes, and the hydrodynamic evolution of the radio lobes within a dense
cluster atmosphere, including an analysis of pressure balance between
the various gaseous components. Also discussed are relativistic
particle acceleration and loss mechanisms in Cygnus A, as well as
magnetic field strengths and geometries both within the radio source,
and in the intracluster medium. We subsequently review the
classification, cluster membership, and the emission components of the
Cygnus A galaxy. The origin of the activity is discussed.
Concentrating on the nuclear regions of the galaxy, we review the
evidence for an obscured QSO, also given the constraints on the
orientation of the radio source axis with respect to the sky plane. We
present an overview of models of central engines in AGN and observations
of Cygnus A which may be relevant to testing such models. We conclude
with a brief section concerning the question of whether Cygnus A is
representative of powerful high redshift radio galaxies.
Received October 10, 1995 相似文献
14.
15.
介绍了MATLAB语言特点和系统建模方法的基本理论.根据南海气象数据的实际建模处理过程,给出了建模的详细步骤及其MATLAB实现过程以及MATLABTM的主要实现程序.试验讨论和结果表明利用MATLAB语言可以方便地对南海气象数据用系统建模方法进行建模和处理,MATLAB在运用系统建模法处理南海气象数据方面具有明显的优越性. 相似文献
16.
青藏块体东北缘断层形变与中强地震 总被引:7,自引:4,他引:3
对祁连山-海原断裂带近期断层形变特征进行了初步研究,发现多场地,大范围的断层活动异常是中等强度地震发生的显著背景,并且往往与大陆地震活动的阶段性总体状况相呼应;区域形变存在明显的特征量,包括特征形态和特征时间,同一场地在不同地震前的异常特征具有重复性,但会受到背景差异显著的不同地震的影响,目前形变状况表明研究区仍具有发生中强地震的地壳运动背景。 相似文献
17.
In the first paper of this series, we presented EBAS – Eclipsing Binary Automated Solver, a new fully automated algorithm to analyse the light curves of eclipsing binaries, based on the ebop code. Here, we apply the new algorithm to the whole sample of 2580 binaries found in the Optical Gravitational Lensing Experiment (OGLE) Large Magellanic Cloud (LMC) photometric survey and derive the orbital elements for 1931 systems. To obtain the statistical properties of the short-period binaries of the LMC, we construct a well-defined subsample of 938 eclipsing binaries with main-sequence B-type primaries. Correcting for observational selection effects, we derive the distributions of the fractional radii of the two components and their sum, the brightness ratios and the periods of the short-period binaries. Somewhat surprisingly, the results are consistent with a flat distribution in log P between 2 and 10 d. We also estimate the total number of binaries in the LMC with the same characteristics, and not only the eclipsing binaries, to be about 5000. This figure leads us to suggest that (0.7 ± 0.4) per cent of the main-sequence B-type stars in the LMC are found in binaries with periods shorter than 10 d. This frequency is substantially smaller than the fraction of binaries found by small Galactic radial-velocity surveys of B stars. On the other hand, the binary frequency found by Hubble Space Telescope ( HST ) photometric searches within the late main-sequence stars of 47 Tuc is only slightly higher and still consistent with the frequency we deduced for the B stars in the LMC. 相似文献
18.
A. Habib J. Vernin Z. Benkhaldoun H. Lanteri 《Monthly notices of the Royal Astronomical Society》2006,368(3):1456-1462
In this paper, we present a new method to estimate, for each turbulent layer labelled i , the horizontal wind speed v ( h i ) , the standard deviation of the horizontal wind speed fluctuations σ v ( hi ) and the integrated value of C 2 n over the thickness Δ hi of the turbulent layer C 2 n ( hi )Δ hi , where hi is the altitude of the turbulent layer. These parameters are extracted from single star scintillation spatiotemporal cross-correlation functions of atmospheric speckles obtained within the generalized mode. This method is based on the simulated annealing algorithm to find the optimal solution required to solve the problem. Astrophysics parameters for adaptive optics are also calculated using C 2 n ( hi ) and v ( hi ) values. The results of other techniques support this new method. 相似文献
19.
20.