全文获取类型
收费全文 | 21012篇 |
免费 | 2848篇 |
国内免费 | 3990篇 |
专业分类
测绘学 | 1040篇 |
大气科学 | 3522篇 |
地球物理 | 4712篇 |
地质学 | 10151篇 |
海洋学 | 2799篇 |
天文学 | 2031篇 |
综合类 | 1472篇 |
自然地理 | 2123篇 |
出版年
2024年 | 64篇 |
2023年 | 282篇 |
2022年 | 859篇 |
2021年 | 1088篇 |
2020年 | 952篇 |
2019年 | 1045篇 |
2018年 | 1330篇 |
2017年 | 1219篇 |
2016年 | 1256篇 |
2015年 | 968篇 |
2014年 | 1250篇 |
2013年 | 1270篇 |
2012年 | 1271篇 |
2011年 | 1361篇 |
2010年 | 1257篇 |
2009年 | 1181篇 |
2008年 | 1146篇 |
2007年 | 1155篇 |
2006年 | 1029篇 |
2005年 | 609篇 |
2004年 | 503篇 |
2003年 | 589篇 |
2002年 | 628篇 |
2001年 | 573篇 |
2000年 | 498篇 |
1999年 | 547篇 |
1998年 | 470篇 |
1997年 | 473篇 |
1996年 | 404篇 |
1995年 | 411篇 |
1994年 | 359篇 |
1993年 | 310篇 |
1992年 | 256篇 |
1991年 | 162篇 |
1990年 | 138篇 |
1989年 | 158篇 |
1988年 | 119篇 |
1987年 | 104篇 |
1986年 | 82篇 |
1985年 | 55篇 |
1984年 | 53篇 |
1983年 | 49篇 |
1982年 | 49篇 |
1981年 | 29篇 |
1980年 | 28篇 |
1979年 | 29篇 |
1978年 | 20篇 |
1977年 | 21篇 |
1975年 | 22篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
61.
Yu. G. Shkuratov K. Muinonen E. Bowell K. Lumme J. I. Peltoniemi M. A. Kreslavsky D. G. Stankevich V. P. Tishkovetz N. V. Opanasenko L. Y. Melkumova 《Earth, Moon, and Planets》1994,65(3):201-246
About a dozen physical mechanisms and models aspire to explain the negative polarization of light scattered by atmosphereless celestial bodies. This is too large a number for the reliable interpretation of observational data. Through a comparative analysis of the models, our main goal is to answer the question: Does any one model have an advantage over the others? Our analysis is based on new laboratory polarimetric and photometric data as well as on theoretical results. We show that the widely used models due to Hopfield and Wolff cannot realistically explain the phase-angle dependence of the degree of polarization observed at small phase angles. The so-called interference or coherent backscattering mechanism is the most promising model. Models based on that mechanism use well-defined physical parameters to explain both negative polarization and the opposition effect. They are supported by laboratory experiments, particularly those showing enhancement of negative polarization with decreasing particle size down to the wavelength of light. According to the interference mechanism, pronounced negative branches of polarization, like those of C-class asteroids, may indicate a high degree of optical inhomogeneity of light-scattering surfaces at small scales. The mechanism also seems appropriate for treating the negative polarization and opposition effects of cometary dust comae, planetary rings, and the zodiacal light. 相似文献
62.
美术与感觉寻求的关系 总被引:1,自引:0,他引:1
阐述了感觉寻求研究中与绘画有关的研究,分析感觉寻求人格与绘画的复杂度、风格倾向、内容的积极性以及艺术的不确定性之间的关系,认为美术学习可能会影响到人格的发展趋势,影响其创造性人格特质的形成。 相似文献
63.
64.
We found the equilibrium conditions for a self-gravitating toroidal vortex by taking thermal pressure into account. These conditions are shown to significantly differ from those for a disk or a sphere. The evolution of a thin vortex turns it into a compact vortex that loses mechanical stability for low masses at a polytropic index γ<4/3 but retains stability for sufficiently high masses and densities determined by the velocity circulation in the vortex. 相似文献
65.
高从堦 《中国海洋湖沼学报》2003,21(1):40-45
Seawater desalination has been people‘s fond dream since ancient times,the dream is now becoming a reality.This paper presents a brief development history of reverse osmosis.Much attention was paid to innovative development in mebranes,modules.equipments and applied technology,including asymmetric and composite membranes,spiral-wound element and hollow fiber module,energy recovery equipments and different technological processes.The extension of reverse osmosis,such as desalination,pre-concentration,integrated processes and nanofiltration,is also briefly mentioned. 相似文献
66.
The dynamical evolution of meteoroid streams associated with cornets Encke, Halley, Machholz 1986 VIII and asteroid Phaethon is discussed. It is shown that the planetary perturbations can greatly increase the streams thickness and each stream may produce several couples of meteor showers active in different seasons of the year. The theoretical and observed data are in a satisfactory accordance. 相似文献
67.
68.
Comparing with lithofacies palaeogeography of several great plains, the authors analyzed four great plains in Quaternary diastrophism, the sedimentary facies, sedimentary environment and their evolution from the independent embryonic and river system of ancient Heilongjiang finally to the Halar highland, Songnen Plain, Sanjiang Plain, the Xingkai Lake Plain and various river systems, collected the unification outside the system of Heilongjiang River to release into the sea, south ancient Xialiao River finally piracy Dongliao River, Xialiao River had released into the sea the ancient water law vicissitude and the evolved rule. 相似文献
69.
A. B. Pushkarev D. C. Gabuzda Yu. N. Vetukhnovskaya V. E. Yakimov 《Monthly notices of the Royal Astronomical Society》2005,356(3):859-871
We present the results of multifrequency (15 + 8 + 5 GHz) polarization Very Long Baseline Array (VLBA) observations of the three BL Lacertae objects 0745+241, 1418+546 and 1652+398 together with 5-GHz VLBI Space Observatory Programme (VSOP) observations of 1418+546 and 1.6- and 5-GHz VSOP observations of the blazar 1055+018. The jets of all these sources have polarization structure transverse to the jet axis, with the polarization E vectors aligned with the jet along the jet spine and 'sheaths' of orthogonal E vectors at one or both edges of the jet. The presence of polarization aligned with the jet near the 'spine' may indicate that the jets are associated with helical B fields that propogate outward with the jet flow; the presence of orthogonal polarization near the edges of the jet may likewise be a consequence of a helical jet B field, or may be owing to an interaction with the ambient medium on parsec scales. We have tentatively detected interknot polarization in 1055+018 with E aligned with the local jet direction, consistent with the possibility that the jet of this source is associated with a helical B field. 相似文献
70.
We study a model of mergers affecting only the progenitors of present E/SO. We adopt the standard scenarios of star formation as prescribed by Guiderdoni & Rocca-Volmerange. The merging process is parametrized under the assumptions of(1) self-similarity of the Schechter MF and(2) mass conservation. Nine models are discussed. The predictions are compared with counts ofB
J
,U
+,F
+,N
+ bands. E/SO mergers account for the excess of the faintest blue galaxies without causing excess in redder bands. However, as we no longer have enough mergers at brighter magnitudes, a plain E/SO merging model fits less tightly for the redshift and the colour distributions. Detection effect, a steeper slope of LF may be ways to improve. Our models predict acceptable merger frequencies atz = 0.5 although some models predict more interacting galaxies than observation atz = 0. 相似文献