全文获取类型
收费全文 | 26922篇 |
免费 | 530篇 |
国内免费 | 321篇 |
专业分类
测绘学 | 762篇 |
大气科学 | 1907篇 |
地球物理 | 5288篇 |
地质学 | 9409篇 |
海洋学 | 2505篇 |
天文学 | 6426篇 |
综合类 | 61篇 |
自然地理 | 1415篇 |
出版年
2022年 | 119篇 |
2021年 | 235篇 |
2020年 | 271篇 |
2019年 | 335篇 |
2018年 | 670篇 |
2017年 | 662篇 |
2016年 | 815篇 |
2015年 | 488篇 |
2014年 | 780篇 |
2013年 | 1400篇 |
2012年 | 882篇 |
2011年 | 1155篇 |
2010年 | 1046篇 |
2009年 | 1370篇 |
2008年 | 1228篇 |
2007年 | 1235篇 |
2006年 | 1194篇 |
2005年 | 894篇 |
2004年 | 903篇 |
2003年 | 807篇 |
2002年 | 745篇 |
2001年 | 638篇 |
2000年 | 659篇 |
1999年 | 574篇 |
1998年 | 573篇 |
1997年 | 537篇 |
1996年 | 405篇 |
1995年 | 405篇 |
1994年 | 420篇 |
1993年 | 321篇 |
1992年 | 317篇 |
1991年 | 267篇 |
1990年 | 314篇 |
1989年 | 280篇 |
1988年 | 256篇 |
1987年 | 283篇 |
1986年 | 245篇 |
1985年 | 324篇 |
1984年 | 343篇 |
1983年 | 336篇 |
1982年 | 319篇 |
1981年 | 254篇 |
1980年 | 270篇 |
1979年 | 220篇 |
1978年 | 210篇 |
1977年 | 217篇 |
1976年 | 180篇 |
1975年 | 195篇 |
1974年 | 178篇 |
1973年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
B. R. Johnson M. E. Abroe P. Ade J. Bock J. Borrill J. S. Collins P. Ferreira S. Hanany A. H. Jaffe T. Jones A. T. Lee L. Levinson T. Matsumura B. Rabii T. Renbarger P. L. Richards G. F. Smoot R. Stompor H. T. Tran C. D. Winant 《New Astronomy Reviews》2003,47(11-12):1067
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress. 相似文献
143.
144.
We describe how a local plasma structure can be changed by a transverse shear flow using numerical simulation to investigate the disturbance process near the magnetopause. The results show that magnetic field lines are bent by transverse shear flow disturbance near the current sheet region. There are multiple bipolar structures of the normal magnetic field in the numerical simulation. We term this new feature as K-point magnetic reconnection, realistic for discussing space observations. 相似文献
145.
A high-velocity ionized outflow and XUV photosphere in the narrow emission line quasar PG1211+143 总被引:1,自引:0,他引:1
K. A. Pounds J. N. Reeves A. R. King K. L. Page P. T. O'Brien M. J. L. Turner 《Monthly notices of the Royal Astronomical Society》2003,345(3):705-713
We report on the analysis of a ∼60-ks XMM–Newton observation of the bright, narrow emission line quasar PG1211+143. Absorption lines are seen in both European Photon Imaging Camera and Reflection Grating Spectrometer spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C. The observed line energies indicate an ionized outflow velocity of ∼24 000 km s−1 . The highest energy lines require a column density of N H ∼ 5 × 1023 cm−2 , at an ionization parameter of log ξ∼ 3.4 . If the origin of this high-velocity outflow lies in matter being driven from the inner disc, then the flow is likely to be optically thick within a radius of ∼130 Schwarzschild radii, providing a natural explanation for the big blue bump (and strong soft X-ray) emission in PG1211+143. 相似文献
146.
147.
A. D. Biggs D. Rusin I. W. A. Browne A. G. de Bruyn N. J. Jackson L. V. E. Koopmans J. P. McKean S. T. Myers R. D. Blandford K.-H. Chae C. D. Fassnacht M. A. Norbury T. J. Pearson P. M. Phillips A. C. S. Readhead P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2003,338(4):1084-1088
148.
The spatial extent of ion cyclotron waves at Io has been interpreted as requiring a multistep acceleration and transport process: exospheric ions are accelerated outward (relative to Jupiter) due to the corotation electric field, neutralized due to charge exchange in the surrounding exosphere, and then reionized after traveling far across magnetic field lines, at which point they generate the waves. The trajectories of the particles away from Io are sensitive to the location of their initial ionization. This paper examines the spatial distributions of fast neutrals produced under varying conditions in order to provide constraints on the possible structure and nature of the Io exosphere. While a rapid onset of cyclotron waves at a specific location around Io can be modeled with a single, point-source region of ions, such as might occur over a volcano, the regional extent of the waves suggests multiple or distributed sources. 相似文献
149.
150.
N. Callegari Jr S. Ferraz-Mello T. A. Michtchenko 《Celestial Mechanics and Dynamical Astronomy》2006,94(4):381-397
This paper considers the dynamics of two planets, as the planets B and C of the pulsar PSR B1257+12, near a 3/2 mean-motion resonance. A two-degrees-of-freedom model, in the framework of the general three-body planar problem, is used and the solutions are analyzed through surfaces of section and Fourier techniques in the full phase space of the system.On the possibility of existence of a fourth planet in distant orbit, see Wolszczan et al., 2000 相似文献