全文获取类型
收费全文 | 90799篇 |
免费 | 1813篇 |
国内免费 | 823篇 |
专业分类
测绘学 | 2692篇 |
大气科学 | 7104篇 |
地球物理 | 18576篇 |
地质学 | 30663篇 |
海洋学 | 7616篇 |
天文学 | 20750篇 |
综合类 | 273篇 |
自然地理 | 5761篇 |
出版年
2021年 | 588篇 |
2020年 | 716篇 |
2019年 | 783篇 |
2018年 | 1667篇 |
2017年 | 1593篇 |
2016年 | 2244篇 |
2015年 | 1489篇 |
2014年 | 2213篇 |
2013年 | 4606篇 |
2012年 | 2327篇 |
2011年 | 3285篇 |
2010年 | 2800篇 |
2009年 | 3966篇 |
2008年 | 3520篇 |
2007年 | 3240篇 |
2006年 | 3312篇 |
2005年 | 2821篇 |
2004年 | 2849篇 |
2003年 | 2662篇 |
2002年 | 2557篇 |
2001年 | 2305篇 |
2000年 | 2281篇 |
1999年 | 2006篇 |
1998年 | 1921篇 |
1997年 | 1929篇 |
1996年 | 1687篇 |
1995年 | 1617篇 |
1994年 | 1469篇 |
1993年 | 1326篇 |
1992年 | 1225篇 |
1991年 | 1125篇 |
1990年 | 1332篇 |
1989年 | 1152篇 |
1988年 | 1049篇 |
1987年 | 1267篇 |
1986年 | 1121篇 |
1985年 | 1369篇 |
1984年 | 1562篇 |
1983年 | 1479篇 |
1982年 | 1384篇 |
1981年 | 1267篇 |
1980年 | 1124篇 |
1979年 | 1062篇 |
1978年 | 1123篇 |
1977年 | 1023篇 |
1976年 | 959篇 |
1975年 | 890篇 |
1974年 | 927篇 |
1973年 | 966篇 |
1972年 | 601篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
31.
J. Raitala 《Earth, Moon, and Planets》1996,74(3):191-214
The intrablock deformation of Meshkenet Tessera on Venus is mostly due to responses of the uppermost surface bedrock to tensional stresses. It is found that complex deformation structures within the highland blocks resemble those of formed in chocolate tablet boudinaging which has taken place after original parallel faulting and bar-like crustal block formation. The high-angle tessera structures with varying cross-cutting relations define styles and locations of multiphase deformation most evidently related to local relaxation of tessera topography. Series of progressive or superposed fracturing events with alternating fault directions took place at high angles during this relaxational deformation. Compressional ridges often surround these tesserae. 相似文献
32.
E. C. Hopewell M. J. Barlow J. E. Drew Y. C. Unruh Q. A. Parker M. J. Pierce P. A. Crowther C. Knigge S. Phillipps A. A. Zijlstra 《Monthly notices of the Royal Astronomical Society》2005,363(3):857-866
We report the discovery of five massive Wolf–Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission-line stars in the Anglo-Australian Observatory United Kingdom Schmidt Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195–6775 Å spectra of the stars are presented and discussed. A WC9 class is assigned to all five stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near-infrared (NIR) excesses characteristic of hot dust emission (as seen in the great majority of known WC9 stars), we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to seven. Reddenings and distances for all five stars are estimated. 相似文献
33.
34.
35.
New determination of the Earth orientation parameters (EOP), based on optical astrometry observations since the beginning of the century, is now under preparation by the Working group established by Commission 19 of the IAU. The Hipparcos catalog is to define the celestial reference frame in which the new series of EOP are to be described, The novelties of the prepared solution are the higher resolution (5 days) and more parameters estimated from the solution (celestial pole offsets, rheological parameters of the Earth, certain instrumental constants). The mathematical model of the solution is described, and the results based on the observations made with 46 instruments at 29 observatories and a preliminary Hipparcos catalog are presented. 相似文献
36.
37.
38.
V. Delouille J. De Patoul J. F. Hochedez L. Jacques J. P. Antoine 《Solar physics》2005,228(1-2):301-321
The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in
temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution
during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum.
We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules
as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with
the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona
at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we
introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis. 相似文献
39.
Matthew J. GENGE Monica M. GRADY Robert HUTCHISON 《Meteoritics & planetary science》1996,31(5):627-632
Abstract— Cosmic dust accreted by the Earth can be extensively reprocessed during atmospheric encounters. The textures and compositions of reprocessed material provide important constraints by which the processes affecting extraterrestrial matter in the Earth's atmosphere can be better understood. Here we report results on an unusual Antarctic glassy cosmic spherule that demonstrates strong textural evidence for at least two grazing incidence encounters with the Earth's atmosphere prior to final reentry. The particle consists of a central glassy core with four peripheral glass lobes that transect a silicate particle rim. The texture of the particle confirms previous theoretical speculations that some high velocity, low incidence angle interplanetary particles experience numerous encounters with the Earth's atmosphere and also indicates that micrometeorites demonstrating multiple melting episodes should be interpreted with caution. 相似文献
40.
In astronomical photometry, the sensitivity of observations is limited by the dark counts of the photomultiplier tube. In the present work, the effect of dark count noise in photon counting systems is investigated by theory and experimental measurements. Dark counts are considered to be originating from two sources, namely: dc fluctuations and random pulses.Experimental measurements were carried out to determine noise effects in different operating regions of noise dominance. The results provide strong evidence that: in normal operating mode, where the effect of random pulses is dominant, dark counts do not follow Poisson statistics. The observed noise shows strong (1/f) power spectrum, where the observed noise power is found to increase with time of observation.The results are important in photon counting systems operating under dark count limited mode. The conclusions drawn can be useful in obtaining more accurate error estimates and in assessing astronomical photometric observations and data reduction techniques. 相似文献