全文获取类型
收费全文 | 133153篇 |
免费 | 2045篇 |
国内免费 | 1688篇 |
专业分类
测绘学 | 3789篇 |
大气科学 | 9301篇 |
地球物理 | 25739篇 |
地质学 | 49764篇 |
海洋学 | 11232篇 |
天文学 | 26989篇 |
综合类 | 2391篇 |
自然地理 | 7681篇 |
出版年
2022年 | 679篇 |
2021年 | 1217篇 |
2020年 | 1304篇 |
2019年 | 1474篇 |
2018年 | 7295篇 |
2017年 | 6399篇 |
2016年 | 5647篇 |
2015年 | 1942篇 |
2014年 | 3233篇 |
2013年 | 5806篇 |
2012年 | 4339篇 |
2011年 | 6979篇 |
2010年 | 6004篇 |
2009年 | 7468篇 |
2008年 | 6381篇 |
2007年 | 6888篇 |
2006年 | 4534篇 |
2005年 | 3529篇 |
2004年 | 3644篇 |
2003年 | 3437篇 |
2002年 | 3261篇 |
2001年 | 2708篇 |
2000年 | 2612篇 |
1999年 | 2085篇 |
1998年 | 2154篇 |
1997年 | 2009篇 |
1996年 | 1696篇 |
1995年 | 1690篇 |
1994年 | 1467篇 |
1993年 | 1427篇 |
1992年 | 1311篇 |
1991年 | 1314篇 |
1990年 | 1294篇 |
1989年 | 1194篇 |
1988年 | 1107篇 |
1987年 | 1291篇 |
1986年 | 1135篇 |
1985年 | 1386篇 |
1984年 | 1562篇 |
1983年 | 1481篇 |
1982年 | 1351篇 |
1981年 | 1333篇 |
1980年 | 1144篇 |
1979年 | 1096篇 |
1978年 | 1052篇 |
1977年 | 966篇 |
1976年 | 928篇 |
1975年 | 903篇 |
1974年 | 887篇 |
1973年 | 961篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
361.
362.
The present work applies the method of characteristics to study the behaviour of planar and cylindrical wave-heads propagating through a perfectly electrically conducting and thermally radiating inviscid gas under the optically thin limit in the presence of a transverse magnetic field. The true nonlinear progress of the flow variable gradients at the wavefront is predicted and the critical distance at which the characteristics pile up at the wavefront to form a shock wave is obtained. It is investigated as to how the effects of radiative flux, the magnetic field strength and the specific heat ratio influence the process of steepening or flattening of the characteristic wavefront. 相似文献
363.
364.
365.
We show how the Yarkovsky effect can be understood as a heat engine. The output of the engine, manifested in the rate of change in semimajor axis of the body, has a maximum at an intermediate heat capacity, depending on the rotation rate of the body. This maximum arises because the work output depends on the product of the solar heat absorbed by the body and transported from its morning to evening side (this am-pm heat flux increases with heat capacity) and the Carnot efficiency (which declines with heat capacity). 相似文献
366.
We performed polarization observations of giant radio pulses from the millisecond pulsar B1937+21. The observations were carried out in July 2002 with the 64-m Kalyazin radio telescope at a frequency of 600 MHz in two polarization channels with left-and right-hand circular polarizations (RCP and LCP). We used the S2 data acquisition system with a time resolution of 125 ns. The duration of an observing session was 20 min. We detected twelve giant radio pulses with peak flux densities higher than 1000 Jy; five and seven of these pulses appeared in the RCP and LCP channels, respectively. We found no event that exceeded the established detection threshold simultaneously in the two polarization channels. Thus, we may conclude that the detected giant pulses have a high degree of circular polarization, with the frequency of occurrence of RCP and LCP pulses being the same. 相似文献
367.
Recently, exact spatially-homogeneous solutions have been found for a conformally invariant massless scalar fieldS(t) coupled to a Robertson-Walker geometry. We investigate extending these solutions to inhomogeneous scalar fieldsS(t, x
l
). For an isotropic scalar fieldS(t, r) we find a solution satisfying three of the five field equations. If we use REDUCE, we show that the remaining equations forceS=S(t). 相似文献
368.
369.
P. A. M. Van Hoof M. E. Foord R. F. Heeter J. E. Bailey H.-K. Chung M. E. Cuneo W. H. Goldstein V. Jonauskas F. P. Keenan R. Kisielius D. A. Liedahl C. Ramsbottom S. J. Rose P. T. Springer R. S. Thoe 《Astrophysics and Space Science》2005,298(1-2):147-153
In experiments at the high-power Z-facility at Sandia National Laboratory in Albuquerque, New Mexico, we have been able to
produce a low density photoionized laboratory plasma of Fe mixed with NaF. The conditions in the experiment allow a meaningful
comparison with X-ray emission from astrophysical sources. The charge state distributions of Fe, Na and F are determined in
this plasma using high resolution X-ray spectroscopy. Independent measurements of the density and radiation flux indicate
unprecedented values for the ionization parameter ξ = 20–25 erg cm s−1 under nearly steady-state conditions. First comparisons of the measured charge state distributions with X-ray photoionization
models show reasonable agreement, although many questions remain. 相似文献