全文获取类型
收费全文 | 318篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
大气科学 | 13篇 |
地球物理 | 43篇 |
地质学 | 73篇 |
海洋学 | 11篇 |
天文学 | 111篇 |
自然地理 | 73篇 |
出版年
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 13篇 |
2013年 | 14篇 |
2012年 | 10篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 4篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1969年 | 4篇 |
1967年 | 2篇 |
1962年 | 2篇 |
1938年 | 4篇 |
1933年 | 3篇 |
排序方式: 共有324条查询结果,搜索用时 546 毫秒
301.
302.
303.
We simultaneously solve the equations of radiative transfer and statistical equilibrium for a model hydrogen atom including Lyman-, Lyman-, Balmer- and the Lyman, Balmer and Paschen continua. The model atmospheres we use are the results of Nakagawa et al. (1973) for a kinematic model of the chromospheric solar flare.We find that the models adequately predict the total intensity of B, its wing broadening, the presence of a red-shifted wing, the maximum electron density, the total line-of-sight second-level population and the narrowness in height of the B emitting region. The profile of B is strongly self-reversed, however, and agrees with observations only in the presence of 40–70 km s–1 macroturbulent motion.We find that Nakagawa et al. (1973) seriously overestimate the radiative loss function, which will have a large effect on their models. Proper radiative loss calculations must be included in any physically realistic model.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
304.
X-radiation may result from active plasma phenomena in the interactions of comets with the solar wind. We have carried out a limited but sensitive search for soft X-radiation from Comet Bradfield (1979
), on 1980 Feb. 5. No X-radiation was detected at a level (3σ) of 1.7 × 10−13 erg(cm2sec keV)−1 in the 0.2 – 4.0 kev range. This corresponds to a limit on the power dissipated in the comet by non-thermal electrons of approximately 1019 ergs sec−1, averaged over the 2568-sec exposure to the comet. This energy deposition is near the magnitude suggested by simple theoretical ideas, and further searches of appropriate comets both in soft X-radiation and at radio wavelengths seem warranted. 相似文献
305.
306.
307.
Laboratory tests show that pulse pile-up requires a significant correction to the response of scintillation counters to solar X-ray bursts with steep energy spectra. The interpretation of the OSO-III and other satellite data in view of these corrections indicates that steep solar X-ray spectra with varying emission measure produce an effect similar to that produced by relatively hard spectra with a constant emission measure. 相似文献
308.
John P. Blakeslee John R. Lucey Brian J. Barris Michael J. Hudson John L. Tonry 《Monthly notices of the Royal Astronomical Society》2001,327(3):1004-1020
We perform a series of comparisons between distance-independent photometric and spectroscopic properties used in the surface brightness fluctuation (SBF) and fundamental plane (FP) methods of early-type galaxy distance estimation. The data are taken from two recent surveys: the SBF Survey of Galaxy Distances and the Streaming Motions of Abell Clusters (SMAC) FP survey. We derive a relation between colour and Mg2 index using nearly 200 galaxies and discuss implications for Galactic extinction estimates and early-type galaxy stellar populations. We find that the reddenings from Schlegel et al. for galaxies with appear to be overestimated by per cent, but we do not find significant evidence for large-scale dipole errors in the extinction map. In comparison with stellar population models having solar elemental abundance ratios, the galaxies in our sample are generally too blue at a given Mg2 ; we ascribe this to the well-known enhancement of the α -elements in luminous early-type galaxies. We confirm a tight relation between stellar velocity dispersion σ and the SBF 'fluctuation count' parameter N¯ , which is a luminosity-weighted measure of the total number of stars in a galaxy. The correlation between N¯ and σ is even tighter than that between Mg2 and σ . Finally, we derive FP photometric parameters for 280 galaxies from the SBF survey data set. Comparisons with external sources allow us to estimate the errors on these parameters and derive the correction necessary to bring them on to the SMAC system. The data are used in a forthcoming paper, which compares the distances derived from the FP and SBF methods. 相似文献
309.
J. A. Hudson 《Geophysical Journal International》1981,67(3):755-770
Summary. A parabolic approximation to the equation of motion of elastic waves as a sum of surface modes and discovering a parabolic approximation be applied directly to surface waves. The approximation depends on the material properties varying slowly within a wavelength, whereas surface waves may travel in a surface wave guide whose depth is of the same order of magnitude as a wavelength. This difficulty is overcome by representing the waves as a sum of surface modes and discovering a parabolic approximation for the amplitudes as a function of position on the surface. The theory is applicable to the propagation of Love or Rayleigh waves in a structure which is vertically stratified in an arbitrary way, but varies slowly in any horizontal direction. 相似文献
310.
Bruce Downing Tim Hudson Peter Taylor Peter Bland Nancy Villanueva 《The Professional geographer》1980,32(4):454-461
A factor analysis of the 1978 Massachusetts election is undertaken to investigate whether the alleged decline of political parties in the United States can be distinguished at the state scale. Four factors are identified, two of which relate to the voting patterns of state-wide candidates. The main factor is easily seen to represent a “party voting”pattern and the fourth factor suggests a nonparty pattern of support associated with the Democratic candidate for governor, Edward King. It is suggested that this separation of the voting pattern for Democratic candidates may possibly reflect party decomposition in Massachusetts. 相似文献