全文获取类型
收费全文 | 27779篇 |
免费 | 5179篇 |
国内免费 | 5596篇 |
专业分类
测绘学 | 2109篇 |
大气科学 | 2598篇 |
地球物理 | 6775篇 |
地质学 | 14570篇 |
海洋学 | 3519篇 |
天文学 | 1955篇 |
综合类 | 2124篇 |
自然地理 | 4904篇 |
出版年
2024年 | 84篇 |
2023年 | 253篇 |
2022年 | 813篇 |
2021年 | 1019篇 |
2020年 | 945篇 |
2019年 | 1232篇 |
2018年 | 1016篇 |
2017年 | 1110篇 |
2016年 | 1179篇 |
2015年 | 1269篇 |
2014年 | 1526篇 |
2013年 | 1473篇 |
2012年 | 1665篇 |
2011年 | 1663篇 |
2010年 | 1467篇 |
2009年 | 1933篇 |
2008年 | 1762篇 |
2007年 | 1989篇 |
2006年 | 2051篇 |
2005年 | 1757篇 |
2004年 | 1685篇 |
2003年 | 1575篇 |
2002年 | 1362篇 |
2001年 | 1147篇 |
2000年 | 1018篇 |
1999年 | 885篇 |
1998年 | 759篇 |
1997年 | 621篇 |
1996年 | 591篇 |
1995年 | 504篇 |
1994年 | 446篇 |
1993年 | 375篇 |
1992年 | 339篇 |
1991年 | 229篇 |
1990年 | 155篇 |
1989年 | 218篇 |
1988年 | 108篇 |
1987年 | 88篇 |
1986年 | 39篇 |
1985年 | 34篇 |
1984年 | 18篇 |
1983年 | 25篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 20篇 |
1979年 | 36篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
长诏断裂带垂直运动与地震关系初探 总被引:5,自引:0,他引:5
黄松风 《大地测量与地球动力学》2003,23(4):99-104
利用跨断层短水准资料分析了长诏断裂带断层活动特征,结果表明:长诏断裂带总体活动性质基本相同.分时段活动性质有所不同。断层各段多数以压性逆断为主,不同于历史地质考察结果。此外,长诏断裂带各断裂都具有分段活动特点。 相似文献
22.
We use the observed polarization properties of a sample of 26 powerful radio galaxies and radio-loud quasars to constrain the conditions in the Faraday screens local to the sources. We adopt the cosmological redshift, low-frequency radio luminosity and physical size of the large-scale radio structures as our 'fundamental' parameters. We find no correlation of the radio spectral index with any of the fundamental parameters. The observed rotation measure is also independent of these parameters, suggesting that most of the Faraday rotation occurs in the Galactic foreground. The difference between the rotation measures of the two lobes of an individual source, as well as the dispersion of the rotation measure, shows significant correlations with the source redshift, but not with the radio luminosity or source size. This is evidence that the small-scale structure observed in the rotation measure is caused by a Faraday screen local to the sources. The observed asymmetries between the lobes of our sources show no significant trends with each other or other source properties. Finally, we show that the commonly used model for the depolarization of synchrotron radio emission by foreground Faraday screens is inconsistent with our observations. We apply alternative models to our data and show that they require a strong increase of the dispersion of the rotation measure inside the Faraday screens with cosmological redshift. Correcting our observations with these models for redshift effects, we find a strong correlation of the depolarization measure with redshift and a significantly weaker correlation with radio luminosity. We do not find any (anti-)correlation of depolarization measure with source size. All our results are consistent with a decrease in the order of the magnetic field structure of the Faraday screen local to the sources for increasing cosmological redshift. 相似文献
23.
24.
We present a new general scheme for calculating the structure and dynamics of radiation-pressure-driven photoionized flows. The new method goes one step beyond the Sobolev approximation. It involves a numerical solution of the radiative transfer in absorption lines, including the effects of differential expansion and line interactions such as line locking and blanketing. We also present a new scheme for calculating the radiation pressure due to trapped line photons in finite, differentially expanding flows. We compare our results for the radiation pressure force with those obtained using the Sobolev approximation and show the limitations of the latter. In particular, we demonstrate that the Sobolev method gives a poor approximation near discontinuity surfaces and its neglect of line blanketing can lead to erroneous results in high-velocity flows. We combine the newly calculated radiation pressure force with self-consistent photoionization and thermal calculations to study the dynamics and spectral features of broad absorption-line flows and highly ionized gas flows in active galactic nuclei (AGN). A comparison with Sobolev-type calculations shows that the latter overestimates the terminal velocity of the flow and, conversely, underestimates its opacity. We also show that line locking on broad emission lines can have a significant effect on the dynamics and spectral features of AGN flows. 相似文献
25.
JINFeng-jun 《中国地理科学(英文版)》2003,13(2):97-103
It is very important to establish cooperative mechanism to guarantee all members to develop their e-conomies in the Yellow Sea Rim. In this paper, the development strategies ofshipplng centers and transportation networkare discussed based on economic giobalization tendency. The results argue that a united transportation network should bebuilt in order to promote the economic competition of Northeast Asia in the world. As a key component of the economiccooperation, a hierarchical shipping centers network should be established with Hong Kong, Shanghai, Pusan, Koho,and Tokyo as cores. The authorities of China, Japan, R. O. Korea and D. P. B. Korea should make more efforts tobuild a set of cooperation institutions based on raising the transportation efficiency. 相似文献
26.
27.
Wei-Hao Bian Quan-Ling Cui Li-Hua Chao Department of Physics Institute of Theoretical Physics Nanjing Normal University Nanjing Key Laboratory for Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2006,6(3):281-286
We used multi-component profiles to model the Hβ and [OⅢ]λλ4959,5007 lines of SDSS J143030.22-001115.1, a narrow-line Seyfert 1 galaxy (NLS1) in a sample of 150 NLS1 candidates selected from the Sloan Digital Sky Survey (SDSS), Early Data Release (EDR). After subtracting the Hβ contribution from narrow line regions (NLRs), we found that its full width half maximum (FWHM) of broad Hβ line is nearly 2900km s~(-1) , significantly larger than the customarily adopted criterion of 2000 km s~(-1) . With its weak Fe Ⅱ multiples, we believe that SDSS J143030.22-001115.1 should not be classified as a genuine NLS1. When we calculate the virial black hole masses of NLS1s, we should use the Hβ linewidth after subtracting the NLR component. 相似文献
28.
MEN Wu ) WEI Hao ) and LIU Guangshan ) * ) College of Oceanography Environmental Science Xiamen University State Key Laboratory of Marine Environmental Science 《中国海洋大学学报(英文版)》2006,5(3):228-234
1Introduction Therearefourradiumisotopesinnature,ofwhich224Ra,226Raand228Rahavebeenwidelyinvestigated inmarineresearch,butthespecificactivityof223Rais toolowtobemeasured,therefore,itsapplicationsarelimited(Moore,1969;Broeckeretal.,1976;KuandLin,1976;Nozak… 相似文献
29.
30.