全文获取类型
收费全文 | 183617篇 |
免费 | 20607篇 |
国内免费 | 43668篇 |
专业分类
测绘学 | 6316篇 |
大气科学 | 31719篇 |
地球物理 | 42183篇 |
地质学 | 86897篇 |
海洋学 | 29486篇 |
天文学 | 35414篇 |
综合类 | 4599篇 |
自然地理 | 11278篇 |
出版年
2022年 | 1294篇 |
2021年 | 2181篇 |
2020年 | 3574篇 |
2019年 | 7195篇 |
2018年 | 9438篇 |
2017年 | 8985篇 |
2016年 | 9812篇 |
2015年 | 7200篇 |
2014年 | 8568篇 |
2013年 | 12671篇 |
2012年 | 9270篇 |
2011年 | 10352篇 |
2010年 | 9859篇 |
2009年 | 10776篇 |
2008年 | 9219篇 |
2007年 | 9057篇 |
2006年 | 8322篇 |
2005年 | 6842篇 |
2004年 | 7162篇 |
2003年 | 6638篇 |
2002年 | 6193篇 |
2001年 | 5395篇 |
2000年 | 4905篇 |
1999年 | 4333篇 |
1998年 | 4547篇 |
1997年 | 4432篇 |
1996年 | 3773篇 |
1995年 | 3603篇 |
1994年 | 3218篇 |
1993年 | 2999篇 |
1992年 | 2759篇 |
1991年 | 2529篇 |
1990年 | 2517篇 |
1989年 | 2168篇 |
1988年 | 1983篇 |
1987年 | 2169篇 |
1986年 | 1914篇 |
1985年 | 2238篇 |
1984年 | 2525篇 |
1983年 | 2271篇 |
1982年 | 2165篇 |
1981年 | 1972篇 |
1980年 | 1807篇 |
1979年 | 1715篇 |
1978年 | 1596篇 |
1977年 | 1450篇 |
1976年 | 1342篇 |
1975年 | 1302篇 |
1974年 | 1285篇 |
1973年 | 1399篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The main properties of the first- and second-order moments of polarized hydrogen lines, forming in the presence of stationary electric and magnetic fields, are reviewed. The analytical results presented here apply directly to the case of optically-thin emission lines in the LTE regime. Some applications of such results to electric- and magnetic-field diagnostics in (solar) plasmas are then briefly considered.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy 相似文献
62.
Sergei A. Klioner 《Celestial Mechanics and Dynamical Astronomy》1996,66(4):345-363
Intermediate orbit for general planetary theory is constructed in the form of multivariate Fourier series with numerical coefficients. The structure and efficiency of the derived series are illustrated by giving various statistical properties of the coefficients.The ability of the recently proposed elliptic function approach to compress the Fourier series representing the intermediate orbit is investigated. Our results confirm that when mutual perturbations of a pair of planets are considered the elliptic function approach is quite efficient and allows one to compress the series substantially. However, when perturbations of three or more planets are under study the elliptic function approach does not give any advantages. 相似文献
63.
64.
1 IntroductionBacteriaandtheiractivitiesplayanimportantroleintheelementalbiogeochemicalcyclesandenergytransformingintheocean (Zhenetal.1 997) .DortchandPackard(1 989) proposedthatfoodwebsintheeutrophicwatersaredominatedbythebiomassofprimaryproducerswhilefoodwebsintheoligotrophicwatersaredominatedbythebiomassofmicrobes.Heterotrophicbacteriahadbeenshowntoplayanimportantroleinthedecompositionoflarge ,rapidlysinkingorganicparticleswithinandbelowtheeuphot iczone ,andfurthertoaffecttheelementaldyn… 相似文献
65.
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
66.
67.
Daniela Lazzaro Marcos A. Florczak Alberto Betzler Othon C. Winter Silvia M. Giuliatti-Winter Claudia A. Angeli Dietmar W. Foryta 《Planetary and Space Science》1996,44(12):1547-1550
The results of photometric observations of comet/asteroid 2060 Chiron at the Observatório do Pico dos Dias (Brazil-OPD) and the Observatoire de Haute-Provence (France-OHP) during 1994 and 1995 are presented. The analysis of the data shows a decrease of 2060 Chiron brightness from its peak values of 1988–1991. The absolute magnitude, Hv, varies from a maximum of 6.6 in February 1994 up to a minimum of 6.8 in June 1995. Therefore 2060 Chiron is back to a minimum of activity close to that of 1983–1985. The slope parameter G is found to be G = 0.71 ± 0.15. It is suggested that the H-G magnitude system, generally adopted to present 2060 Chiron brightness, is not the most appropriate due to the cometary activity of this object. 相似文献
68.
The observed times of minimum light derived from the photometry of the Wolf-Rayet eclipsing binary stars CQ Cep and V444 Cyg are used to estimate the mass-loss rate of the Wolf-Rayet components in several modes of mass-loss and mass-exchange. 相似文献
69.
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
70.