全文获取类型
收费全文 | 73997篇 |
免费 | 2348篇 |
国内免费 | 2605篇 |
专业分类
测绘学 | 2163篇 |
大气科学 | 6253篇 |
地球物理 | 14568篇 |
地质学 | 30221篇 |
海洋学 | 5948篇 |
天文学 | 14641篇 |
综合类 | 1164篇 |
自然地理 | 3992篇 |
出版年
2022年 | 646篇 |
2021年 | 879篇 |
2020年 | 876篇 |
2019年 | 967篇 |
2018年 | 4344篇 |
2017年 | 4004篇 |
2016年 | 3186篇 |
2015年 | 1229篇 |
2014年 | 1787篇 |
2013年 | 2742篇 |
2012年 | 2781篇 |
2011年 | 4736篇 |
2010年 | 4300篇 |
2009年 | 4947篇 |
2008年 | 4067篇 |
2007年 | 4641篇 |
2006年 | 2116篇 |
2005年 | 1991篇 |
2004年 | 1886篇 |
2003年 | 1875篇 |
2002年 | 1677篇 |
2001年 | 1308篇 |
2000年 | 1301篇 |
1999年 | 1227篇 |
1998年 | 1194篇 |
1997年 | 1166篇 |
1996年 | 982篇 |
1995年 | 957篇 |
1994年 | 923篇 |
1993年 | 762篇 |
1992年 | 671篇 |
1991年 | 642篇 |
1990年 | 694篇 |
1989年 | 579篇 |
1988年 | 562篇 |
1987年 | 642篇 |
1986年 | 531篇 |
1985年 | 654篇 |
1984年 | 730篇 |
1983年 | 694篇 |
1982年 | 615篇 |
1981年 | 644篇 |
1980年 | 523篇 |
1979年 | 485篇 |
1978年 | 481篇 |
1977年 | 436篇 |
1976年 | 425篇 |
1975年 | 422篇 |
1974年 | 402篇 |
1973年 | 432篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Earth, Moon, and Planets - 相似文献
12.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars. 相似文献
13.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
14.
1 INTRODUCTION Blazars, including BL Lac objects, highly polarized and optically violently variable quasars,and flat-spectrum radio quasars (FSRQs), are characterized by highly variable non-thermalemission which dominates their characteristics from radio to y-ray bands. The mechanismbelieved to be responsible for their broadband emission is synchrotron radiation followed by in-verse Compton (IC) scattering at higher energies (e.g. Blandford & Konigl 1979). Relativisticbeaming of a jet… 相似文献
15.
The Cassini spacecraft, en route to Saturn, passed close to Jupiter while the Galileo spacecraft was completing its 28th and 29th orbits of Jupiter, thus offering a unique opportunity for direct study of the solar wind-Jovian interaction. Here evidence is given of response of the Jovian magnetopause and bow shock positions to changes of the north-south component of the solar wind magnetic field, a phenomenon long known to occur in equivalent circumstances at Earth. The period analyzed starts with the passage over Cassini of an interplanetary shock far upstream of Jupiter. The shock's arrival at Galileo on the dusk-flank of the magnetosphere caused Galileo to exit into the solar wind. Using inter-spacecraft timing based on the time delay established from the shock arrival at each spacecraft, we point out that Galileo's position with respect to the Jovian bow shock appears to correlate with changes in the disturbed north-south reversing field seen behind the shock. We specifically rule out the alternative of changes in the shape of the bow shock with rotations of the interplanetary magnetic field as the cause. 相似文献
16.
17.
18.
利用“地震预报计算机专家系统”的思想对大同 -阳高 Ms6 .1地震前每一前兆异常事件进行综合评估 ,以每一异常的最可能发震时间来计算发震概率 ,利用地震前兆综合加权信息熵研究了系统熵值与地震的关系。对华北地区的地震前兆综合加权信息熵研究表明 ,在大同 -阳高 Ms6 .1地震前 ,信息熵出现了明显的减熵有序变化 相似文献
19.
Isolation of resonance in acoustic backscatter from elastic targetsusing adaptive estimation schemes
It has been shown that at certain frequencies the acoustic backscatter from elastic targets exhibits certain resonance behavior which closely relates to the physical properties of the target such as dimension, thickness, and composition. The purpose of this paper is to develop an automated approach for identifying the presence of resonance in the acoustic backscatter from an unknown underwater target by isolating the resonance part from the specular contribution. An adaptive transversal filter structure is used to estimate the specular part of the backscatter and consequently the error signal would provide an estimate of the resonance part. An important aspect of this scheme lies in the fact that it does not require an underlying model for the elastic return. The adaptation rule is based upon fast recursive least squares (RLS) learning. The approach taken in this paper is general in the sense that it can be applied to targets of unknown geometry and thickness and, further, does not require any a priori information about the target and/or the environment. Test results on acoustic data are presented which indicate the effectiveness of the proposed approach 相似文献
20.
CHANGE OF NUTRIENT IMPORT AND EXPORT IN PROCESS OF RAINFALL IN AILAO MOUNTAIN OF YUNNAN PROVINCEGanJianmin(甘健民);XueJingyi(薛敬意... 相似文献