全文获取类型
收费全文 | 72634篇 |
免费 | 965篇 |
国内免费 | 520篇 |
专业分类
测绘学 | 1912篇 |
大气科学 | 5481篇 |
地球物理 | 13945篇 |
地质学 | 25094篇 |
海洋学 | 6205篇 |
天文学 | 16711篇 |
综合类 | 162篇 |
自然地理 | 4609篇 |
出版年
2021年 | 535篇 |
2020年 | 597篇 |
2019年 | 600篇 |
2018年 | 1433篇 |
2017年 | 1416篇 |
2016年 | 1736篇 |
2015年 | 1059篇 |
2014年 | 1820篇 |
2013年 | 3669篇 |
2012年 | 1868篇 |
2011年 | 2514篇 |
2010年 | 2305篇 |
2009年 | 3001篇 |
2008年 | 2719篇 |
2007年 | 2690篇 |
2006年 | 2545篇 |
2005年 | 2186篇 |
2004年 | 2143篇 |
2003年 | 1996篇 |
2002年 | 1916篇 |
2001年 | 1780篇 |
2000年 | 1672篇 |
1999年 | 1521篇 |
1998年 | 1443篇 |
1997年 | 1494篇 |
1996年 | 1202篇 |
1995年 | 1221篇 |
1994年 | 1164篇 |
1993年 | 1022篇 |
1992年 | 1005篇 |
1991年 | 947篇 |
1990年 | 1057篇 |
1989年 | 944篇 |
1988年 | 918篇 |
1987年 | 1020篇 |
1986年 | 869篇 |
1985年 | 1159篇 |
1984年 | 1264篇 |
1983年 | 1239篇 |
1982年 | 1185篇 |
1981年 | 1096篇 |
1980年 | 1035篇 |
1979年 | 949篇 |
1978年 | 932篇 |
1977年 | 858篇 |
1976年 | 806篇 |
1975年 | 730篇 |
1974年 | 798篇 |
1973年 | 787篇 |
1972年 | 495篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
771.
Adiabatic indices for a non-dissipative anisotropic convecting plasma are analyzed, and general expressions for the effective adiabatic index and the partial adiabatic indices parallel (γ∥) and perpendicular (γ⟂) to the magnetic field are obtained. It is shown that, in the general case, the value of the effective adiabatic index is not an universal constant and depends on the plasma temperature anisotropy and on the properties of the plasma motion. The values of γ⟂ and γ∥ are shown to be independent of the plasma parameters being completely determined by the characteristics of the plasma flow. 相似文献
772.
In this review paper we discuss several aspects of magnetic reconnection theory, focusing on the field-line motions that are
associated with reconnection. A new exact solution of the nonlinear MHD equations for reconnective annihilation is presented which represents a two-fold generalization of the previous solutions. Magnetic reconnection at null points by
several mechanisms is summarized, including spine reconnection, fan reconnection and separator reconnection, where it is pointed out that two common features of separator reconnection are the rapid flipping of magnetic field lines
and the collapse of the separator to a current sheet. In addition, a formula for the rate of reconnection between two flux
tubes is derived. The magnetic field of the corona is highly complex, since the magnetic carpet consists of a multitude of
sources in the photosphere. Progress in understanding this complexity may, however, be made by constructing the skeleton of the field and developing a theory for the local and global bifurcations between the different topologies. The eruption
of flux from the Sun may even sometimes be due to a change of topology caused by emerging flux break-out. A CD-ROM attached to this paper presents the results of a toy model of vacuum reconnection, which suggests that rapid flipping
of field lines in fan and separator reconnection is an essential ingredient also in real non-vacuum conditions. In addition,
it gives an example of binary reconnection between a pair of unbalanced sources as they move around, which may contribute significantly to coronal heating. Finally,
we present examples in TRACE movies of geometrical changes of the coronal magnetic field that are a likely result of large-scale
magnetic reconnection.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005248007615 相似文献
773.
774.
775.
There are three major issues in modeling solar evanescent oscillations: the variation of the intensity [I]–velocity [V] phase difference of p-modes close to the base of photosphere; the existence of a plateau of negative I–V phase differences below and between the ridges of the low-frequency p-modes; the explanation of the I–V cross-spectra of the evanescent oscillations. We present new interpretations for the first two issues, based on modeling intensity fluctuations taking steep temperature gradients, opacity, and non-adiabatic cooling into account. We also discuss consequences of our model for the explanation of power spectra and cross-power spectra of p-modes. In particular, we present evidence that the acoustic sources that generate evanescent waves produce a coherent background that explains the plateau–interridge regime of negative I–V phase difference. 相似文献
776.
The dynamical properties of electromagnetic (EM) waves in ultra-relativistic electron-positron (EP) plasmas are analytically investigated on the basis of the nonlinear governing equations obtained from a kinetic way. It is shown that the EM wave envelope will collapse and be trapped into a localized region for the modulation interaction with low frequency density variation induced by ponderomotive force. The correlation between the localized strong wave field and the pulsar radio emission is discussed. 相似文献
777.
R. A. Heath 《Marine Geodesy》2013,36(4):337-350
Tide gauge records from several New Zealand east coast ports show persistent oscillations in sea level with a period of 2.4–2.7 h. These are superimposed on local resonant oscillations, and appear to be associated with edge wave excitation on the continental shelf, possibly by meteorological disturbances. A shelf response is also excited by tsunamis. 相似文献
778.
A 35 mm camera system has been developed to operate to depths of 4,000 m. The system takes up to 24 pictures at one lowering, and uses standard torch batteries which last more than 10 lowerings. 相似文献
779.
Kopylov A. I. Kosolapov D. B. Zabotkina E. A. Romanenko A. V. Sazhin A. F. 《Oceanology》2021,61(2):220-232
Oceanology - The distribution of heterotrophic bacteria, viruses, and heterotrophic nanoflagellates was studied in the shelf waters of the East Siberian Sea along the meridional transect from the... 相似文献
780.
Glukhov A. N. Kotov A. B. Priymenko V. V. Sal’nikova E. B. Ivanova A. A. Plotkina Yu. V. Fedoseenko A. M. 《Geotectonics》2022,56(2):178-190
Geotectonics - In our study we analyzed the composition of granitoid rocks within the Kongo magmatic zone of the Omolon median mass. The studied calc-alkaline granitoids cut through the Early... 相似文献