全文获取类型
收费全文 | 747篇 |
免费 | 21篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 48篇 |
地球物理 | 170篇 |
地质学 | 252篇 |
海洋学 | 91篇 |
天文学 | 125篇 |
综合类 | 3篇 |
自然地理 | 75篇 |
出版年
2021年 | 8篇 |
2020年 | 17篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 13篇 |
2016年 | 15篇 |
2015年 | 19篇 |
2014年 | 11篇 |
2013年 | 33篇 |
2012年 | 14篇 |
2011年 | 31篇 |
2010年 | 25篇 |
2009年 | 27篇 |
2008年 | 31篇 |
2007年 | 24篇 |
2006年 | 14篇 |
2005年 | 25篇 |
2004年 | 26篇 |
2003年 | 34篇 |
2002年 | 31篇 |
2001年 | 17篇 |
2000年 | 31篇 |
1999年 | 23篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1971年 | 7篇 |
1970年 | 4篇 |
排序方式: 共有779条查询结果,搜索用时 15 毫秒
121.
S. C. Robinson 《Mathematical Geology》1970,2(4):377-397
Much effort is presently being given in Canada to the development of a national system for storage and retrieval of geologic data. Coordination of these efforts is directed by the secretariat of the National Institute for Geoscience Data under guidance of the Geological Survey of Canada. Most files are project oriented but archival files are justified for data whose observations cannot be repeated, such as those for mineral deposits. Presently, extensive file systems have been created for storage of information obtained in petroleum exploration and exploitation, mineral deposits, field mapping, and geochemistry and geophysics. A Canadian Index to Geoscience Data has been prepared and contains references to all maps and reports, published or unpublished, data banks, and all documents on open file for the federal and provincial agencies.SAFRAS, a general, self-adaptive free-format retrieval and storage system, is employed to retrieve data in plain language. Although geologists are using data systems, it will be the coming generation of geologists who will make maximum use of data processing in geology.presented to the Geological Society of Washington, 8 December 1969. 相似文献
122.
P. A. Robinson 《Solar physics》1992,139(1):147-163
A model is developed for the clumpy Langmuir waves observed in type III source regions. In this model the waves are generated by instability of a beam which propagates outward from the Sun in a state close to marginal stability. Ambient density perturbations cause fluctuations about the marginally stable state, leading to nonuniformities in both beam and waves and, hence, to spatially inhomogeneous growth. High damping rates and high wave levels are strongly anti-correlated, leading to suppression of the net damping. Below saturation stochastic growth causes the waves to follow a random walk in the logarithm of their energy density and the resulting probability of observing a field of magnitude E is approximately proportional to E
-1. Comparison with observations shows that this model can account for the levels and clumpiness of the Langmuir waves, the small net dissipation required for the beams to propagate to 1 AU, the characteristic decay time of type III electromagnetic emission, and the negative mean growth rate observed in situ in type III sources. At 1 AU only the very highest fields approach the threshold for nonlinear wave collapse, but this threshold may be more commonly exceeded closer to the Sun. 相似文献
123.
The question of what lies ahead is of particular concern for Latin Americanists. The last decade has witnessed a serious erosion of both the popularity of their specialty, and an equally troublesome reduction in employment opportunities. This paper uses Association of American Geographers (AAG) data bases to document the age-gender structure of contemporary Latin Americanist geographers, and projects likely compositional changes through the end of the century. 相似文献
124.
R. D. Robinson 《Solar physics》1978,56(2):405-416
A model for the solar Type V event is developed. This model assumes that the basic difference between Type III and Type V bursts is the evolution of the electron beam. For a Type V this beam rapidly elongates, so that it takes progressively longer times to pass higher plasma levels. Physical process influencing the beam development, including Coulomb collisions, non-linear interactions with Langmuir waves and wave-particle scattering from various hydromagnetic wave modes is discussed. The model is compared with previously derived models and with observations.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation. 相似文献
125.
A new approach to the theory of mode coupling in an inhomogeneous, birefringent medium is used to treat mode coupling in a magnetized plasma with a twisted magnetic field. The twist introduces a resonance, corresponding to the rate of twisting being equal to the rate of generalized Faraday rotation. When this resonance occurs it introduces a new regime of strong mode coupling. The implications of this regime are discussed in connection with the long-standing problem in solar radiophysics that mode coupling appears to be stronger than theory implies, but no obvious resolution of the problem is found. 相似文献
126.
127.
128.
High-resolution imaging acquired with the Near Earth Asteroid Rendezvous Shoemaker (NEAR Shoemaker) spacecraft is used to elucidate the spectral properties and spatial distribution of color units on Asteroid 433 Eros. Previous workers mapped four distinct types of color units on the surface (bright streaks, dark soils, ponded materials, average regolith). These units exhibit albedo and color boundaries but there is no evidence to indicate they represent distinct rock types. Rather the units are thought to show evidence of complex regolith transport and sorting processes. Here we report the results of a comprehensive study of all viable color MultiSpectral Imager (MSI) data to identify and characterize the distribution and nature of color units across the whole asteroid. Due to a spacecraft upset that resulted in contamination of the MSI optics, color images are affected with a scattered light problem that hampers interpretation of subtle color contrasts, even after a rigorous remediation. To constrain interpretations of the MSI color data we characterize this residual scattered light and demonstrate how complete correction would affect derived color ratios. Results of our comprehensive study are consistent with previous mapping—confirming that bright streaks, average regolith and dark soils fall on a mixing line, consistent with space weathering effects. We find that the ponded deposits do not fall on this putative mixing line. The color and reflectance of the ponded deposits are consistent with some combination of compositional, grain size and maturity variations from the average regolith. Additionally we show that spectral separation of the four units on ratio plots would only increase with full removal of residual scattered light, especially for features that are small in terms of pixels. Global analysis of the Eros color units illustrates complex regolith processes and grain sorting that may hold clues to understanding space weathering processes and the link between asteroids and meteorites. 相似文献
129.
130.