全文获取类型
收费全文 | 24473篇 |
免费 | 4260篇 |
国内免费 | 7256篇 |
专业分类
测绘学 | 709篇 |
大气科学 | 644篇 |
地球物理 | 1964篇 |
地质学 | 22248篇 |
海洋学 | 2384篇 |
天文学 | 5226篇 |
综合类 | 1406篇 |
自然地理 | 1408篇 |
出版年
2024年 | 104篇 |
2023年 | 342篇 |
2022年 | 739篇 |
2021年 | 893篇 |
2020年 | 854篇 |
2019年 | 1028篇 |
2018年 | 854篇 |
2017年 | 839篇 |
2016年 | 1043篇 |
2015年 | 1120篇 |
2014年 | 1598篇 |
2013年 | 1540篇 |
2012年 | 1650篇 |
2011年 | 1803篇 |
2010年 | 1781篇 |
2009年 | 1987篇 |
2008年 | 1830篇 |
2007年 | 1871篇 |
2006年 | 1723篇 |
2005年 | 1574篇 |
2004年 | 1423篇 |
2003年 | 1247篇 |
2002年 | 1104篇 |
2001年 | 1076篇 |
2000年 | 984篇 |
1999年 | 932篇 |
1998年 | 738篇 |
1997年 | 554篇 |
1996年 | 529篇 |
1995年 | 414篇 |
1994年 | 378篇 |
1993年 | 339篇 |
1992年 | 247篇 |
1991年 | 199篇 |
1990年 | 132篇 |
1989年 | 124篇 |
1988年 | 95篇 |
1987年 | 68篇 |
1986年 | 61篇 |
1985年 | 38篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 17篇 |
1973年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
K. Nagamine † M. Fukugita R. Cen J.P. Ostriker 《Monthly notices of the Royal Astronomical Society》2001,327(1):L10-L14
The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Λ cold dark matter universe with the aid of a stellar population synthesis model. At , the resulting B -band luminosity function has a flat faint-end slope of with the characteristic luminosity and the normalization in fair agreement with observations, while the dark matter halo mass function is steep with a slope of . The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from to 5. A large evolution of the characteristic mass in the stellar mass function as a result of number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from to 2, and then declines towards higher redshift, while the B -band luminosity density continues to increase from to 5 (but only slowly at . 相似文献
73.
The analyses of X-ray emission from classical novae during the outburst stage have shown that the soft X-ray emission below 1 keV, which is thought to originate from the photosphere of the white dwarf, is inconsistent with the simple blackbody model of emission. Thus, ROSAT Position Sensitive Proportional Counter (PSPC) archival data of the classical Nova Mus 1983 (GQ Mus) have been re-analysed in order to understand the spectral development in the X-ray wavelengths during the outburst stage. The X-ray spectra are fitted with the hot white dwarf (WD) atmosphere emission models developed for the remnants of classical novae near the Eddington luminosity. The post-outburst X-ray spectra of the remnant white dwarf are examined in the context of evolution on the Hertzsprung–Russell diagram using C–O enhanced atmosphere models. The data obtained in 1991 August (during the ROSAT All Sky Survey) indicate that the effective temperature is . The 1992 February data show that the white dwarf had reached an effective temperature in the range with an unabsorbed X-ray flux (i.e. ∼ bolometric flux) between and . We show that the H burning at the surface of the WD had most likely ceased at the time of the X-ray observations. Only the 1991 August data show evidence for ongoing H burning. 相似文献
74.
探讨用遗传算法对数学模型进行优化。考虑到控制系统稳健性的要求 ,用遗传算法寻找出控制系统最佳稳定域 ,实现控制系统数学模型的寻优。阐述了用遗传算法求解问题的步骤和参数的取值 ,并用仿真实验对优化结果进行了检验。结果表明 :在控制系统数学模型的优化中 ,遗传算法具有其他算法无可比拟的优越性。 相似文献
75.
76.
77.
T.D. Thoroughgood V.S. Dhillon S.P. Littlefair T.R. Marsh D.A. Smith 《Monthly notices of the Royal Astronomical Society》2001,327(4):1323-1333
We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi-amplitude of the primary star was found to be from the motion of the wings of the He ii λ 4686-Å emission line. By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be . From these parameters, we obtain a mass of for the white dwarf primary star and a mass of for the secondary star. The radius of the secondary is calculated to be , confirming that it is evolved. The inclination of the system is calculated to be , consistent with the deep eclipse seen in the light-curves. The helium emission lines are double-peaked, with the blueshifted regions of the disc being eclipsed prior to the redshifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within ∼700 000 yr. 相似文献
78.
矿床谱系是对成矿多样性的理论概括,而成矿多样性又是由不同级别、不同性质的致矿地质异常决定的.本文论述了山东省内生金矿矿床谱系及其致矿地质异常. 相似文献
79.
80.
Prediction of Stellar Atmospheric Parameters using Instance-Based Machine Learning and Genetic Algorithms 总被引:1,自引:0,他引:1
In this article we present a method for the automated prediction of stellar atmospheric parameters from spectral indices.
This method uses a genetic algorithm (GA) for the selection of relevant spectral indices and prototypical stars and predicts
their properties, using the k-nearest neighbors method (KNN). We have applied the method to predict the effective temperature,
surface gravity, metallicity, luminosity class and spectral class of stars from spectral indices. Our experimental results
show that the feature selection performed by the genetic algorithm reduces the running time of KNN up to 92%, and the predictive
accuracy error up to 35%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献