全文获取类型
收费全文 | 62996篇 |
免费 | 6666篇 |
国内免费 | 9329篇 |
专业分类
测绘学 | 3262篇 |
大气科学 | 9669篇 |
地球物理 | 13794篇 |
地质学 | 31069篇 |
海洋学 | 5751篇 |
天文学 | 4626篇 |
综合类 | 5367篇 |
自然地理 | 5453篇 |
出版年
2024年 | 125篇 |
2023年 | 573篇 |
2022年 | 1679篇 |
2021年 | 1927篇 |
2020年 | 1735篇 |
2019年 | 1820篇 |
2018年 | 6627篇 |
2017年 | 5768篇 |
2016年 | 4593篇 |
2015年 | 2078篇 |
2014年 | 2444篇 |
2013年 | 2435篇 |
2012年 | 3183篇 |
2011年 | 4882篇 |
2010年 | 4190篇 |
2009年 | 4461篇 |
2008年 | 3845篇 |
2007年 | 4229篇 |
2006年 | 1812篇 |
2005年 | 1458篇 |
2004年 | 1428篇 |
2003年 | 1518篇 |
2002年 | 1397篇 |
2001年 | 1149篇 |
2000年 | 1273篇 |
1999年 | 1713篇 |
1998年 | 1377篇 |
1997年 | 1373篇 |
1996年 | 1225篇 |
1995年 | 1103篇 |
1994年 | 1026篇 |
1993年 | 854篇 |
1992年 | 695篇 |
1991年 | 524篇 |
1990年 | 405篇 |
1989年 | 397篇 |
1988年 | 338篇 |
1987年 | 229篇 |
1986年 | 200篇 |
1985年 | 145篇 |
1984年 | 107篇 |
1983年 | 95篇 |
1982年 | 107篇 |
1981年 | 99篇 |
1980年 | 69篇 |
1979年 | 54篇 |
1978年 | 27篇 |
1976年 | 29篇 |
1975年 | 24篇 |
1958年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
A solar flare with both H and Fe i 5324 emissions was observed in AR 7529 (S13, E65) on 24 June, 1993 at the Bejing Astronomical Observatory. Our calculations show that the Fe i 5324 emission region of the flare was located in the low photosphere at a height of about 180 km above 5000 = 1, which is lower than many previous studies of white-light flares. To study a Fe i 5324 flare, which represents a kind of extreme case in solar flares, would be useful for clarifying some arguments in the researches of white-light flares as well as for understanding the mechanism of solar flares.The synthetic analyses from vairous features of the flare lead to the following possible exciting mechanism of the Fe i 5324 flare: owing to the flow of energetic electrons from the corona and probably also the thermal conduction downward into the lower atmosphere, a condensation with a temperature higher than that below it was formed near the transition region. Then the low photosphere was heated through backwarming. The Fe i 5324 flare occurred as an indicator of the excitation in the low photosphere. 相似文献
992.
993.
Yu -Qing Lou 《Astrophysics and Space Science》1994,222(1-2):231-234
The forthcoming collision by debris of P/Shoemaker-Levy 9 comet with Jupiter during the week of July 18, 1994 has generated considerable scientific and public interest. This collision may release an amount of energy ranging from 1025-1031 ergs in the Jovian atmosphere. Two possible phenomena associated with this event are described in this Letter to the Editor. The first one is the likely display of deformed Jovian magnetic field lines as the comet interacts with the Jovian magnetosphere. The second one is electromagnetic radiation outbursts during comet explosions over a wide frequency range from radio up to gamma ray emissions. If relativistic electrons with energies up to ~ 1000 MeV could be produced during comet explosions, then synchrotron radiations with frequencies from radio up to infrared range could be detectable. Hard X-rays and gamma rays could be produced by bremsstrahlung and inverse Compton processes. Since one cannot exclude the possible transient presence of relativistic electrons with Lorentz factor 2 × 106, synchrotron radiation component might even be extended into gamma ray frequency range during intermittent short time intervals. 相似文献
994.
995.
996.
In the framework of the MIT bag model we consider absolutely stable strange quark matter consisting of u, d, and s quarks and electrons. For a realistic range of parameters of the quark bag we compute the threshold density for the appearance of strange quark matter that is realized on the surface of self-sustaining strange stars. On the basis of twelve calculated equations of state we give a detailed study of the series of configurations of strange stars consistent with the best known observational data. We show that the binding energy of the models depends essentially on the quark-gluon interaction constant c.Translated fromAstrofizika, Vol. 37, No. 3, 1994.The authors are grateful to E. V. Chubaryan and A. M. Atoyan for assistance in overcoming the information blockade. The present paper was written in the framework of area 46/101 93-353, supported by the Ministry of Higher Education and Science of the Republic of Armenia. 相似文献
997.
The densities of 36 water samples from the Huanghe River estuary and Bohai Bay were determinedby a magnetic float densimcter under three temperatures from 15℃ to 25℃.All the measured densities ofsamples were greater than that of the values calculated from the International Equation of State of Seawater.The differences between the measured and calculated densities increased with the decrease of salinities.The dif-ferences appeared exponentially correlated with[Ca~(2+)]/s,[Mg~(2+)]/s and[SO_4~(2-)]/s,and had"s"type curverelationship with the alkalinity in all salinity range.But in the salinity ranging from 25.72 to 31.57,therelationships were all linear.The density difference can be estimated from the equation △ρ(10~3kg·m~(-3))=(-2.79+236.5([Ca~(2+)]/s)/(-9.7464×10~(-3)+[Ca~(2+)]/s).It was the high alkalinity and[Ca~(2+)]/s that resulted in the measured densi-ties of seawaters being higher than the calculated densities in the Huanghe estuary and Bohai Bay. 相似文献
998.
Hongqi Zhang 《Solar physics》1994,154(2):207-214
A set of H chromospheric magnetograms at various wavelengths near the line center, chromospheric Dopplergrams, and photospheric vector magnetograms of a unipolar sunspot region near the solar limb were obtained with the vector video magnetograph at the Huairou Solar Observing Station. The superpenumbral chromospheric magnetic field is almost parallel to the surface at the outside of the sunspot penumbra, where the magnetic lines of force are mainly concentrated in the superpenumbral filaments. In the gaps between the filaments the chromospheric horizontal field is weak. 相似文献
999.
用褶积滤波处理井水位对固体潮响应的滞后 总被引:2,自引:1,他引:1
本文给出了一种用褶积滤波处理井水位对固体潮响应滞后的新方法。鲁07井水位观测资料用这种方法处理比一般回归方法的平均中误差少4.6mm。文中讨论了褶积滤波积分区间长度与水井含水层渗透系数的关系及褶积滤波比别尔采夫滤波的优越性。 相似文献
1000.
本文介绍了鲁23井“动水位”观测情况。提出了一个分析有泄流的“动水位”的新方法,即把流量换算成水位,以等效静水位来表示“动水位”与流量。由于把“动水位”与流量用一个量来计算,从而为“动水位”观测定量的、统一的分析研究提供了新的方法。这对提高“动水位”井的监测预报地震能力起一定的作用。 本文还以鲁23井“动水位”观测资料为例,利用新方法进行处理的观测分析结果与理论研究结果是一致的。 相似文献