全文获取类型
收费全文 | 857篇 |
免费 | 29篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 80篇 |
地球物理 | 214篇 |
地质学 | 270篇 |
海洋学 | 88篇 |
天文学 | 103篇 |
综合类 | 4篇 |
自然地理 | 122篇 |
出版年
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 18篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 25篇 |
2015年 | 27篇 |
2014年 | 22篇 |
2013年 | 51篇 |
2012年 | 33篇 |
2011年 | 35篇 |
2010年 | 33篇 |
2009年 | 41篇 |
2008年 | 30篇 |
2007年 | 47篇 |
2006年 | 25篇 |
2005年 | 31篇 |
2004年 | 25篇 |
2003年 | 32篇 |
2002年 | 31篇 |
2001年 | 31篇 |
2000年 | 19篇 |
1999年 | 25篇 |
1998年 | 21篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1973年 | 10篇 |
1969年 | 3篇 |
1947年 | 3篇 |
排序方式: 共有889条查询结果,搜索用时 15 毫秒
121.
The dates of recession of eleven outlet glaciers of the Hielo Patagónico Norte (Northern Patagonian Icefield) from their recent maximum positions have been inferred from dendrochronology, lichenometry, radiocarbon dating and historical sources. We have refined the dating for part of the Little Ice Age period in this area placing a glacial advance to between AD 1650 and 1766 with the latter date favoured as conformable with historical records and an uncalibrated radiocarbon determination. Glacier recession from maximal positions began in the early 1860s–1870s. Recession was largely synchronous on the western and eastern sides of the Icefield. This synchronicity suggests that climate forcing over-rides second-order controls on glacier behaviour such as the nature of the terminal environment (e.g. calving/non-calving) or differences in glacier drainage basin area. We argue that this icefield-wide glacier recession represents a response to post-Little Ice Age warming, and provides further evidence for the global extent and near synchronous termination of the Little Ice Age. 相似文献
122.
Summary. The frozen flux approximation of Roberts & Scott is a constraint on the core field that can be used to aid interpretation of the very sparse datasets that palaeomagnetism and archaeomagnetism provide. It gives bounds on the size of the components of the magnetic field at a point, of the Gauss coefficients, and, if valid over such long time periods, limits the shape of the field during transitions between normal and reversed polarities. The maximum intensity at a point, consistent with the present flux, is 281 μT or 4 times the maximum field observed today. The present dipole is about 50 per cent of its upper bound. Polarity reversal is impossible if the transition field is purely axisymmetric. None of the measurements we consider violate the frozen flux approximation. 相似文献
123.
124.
Neil Kennan 《The Australian geographer》1988,19(2):284-289
The implementation of an ‘appropriate’ housing subdivision in Lae, Papua New Guinea represents a new approach in creating an acceptable environment for the urban poor. The unique hexagonal design of the Tensiti development and its aims and policy implications are discussed. It appears that at least some of the urban poor of Lae now live in a settlement which satisfies the demands of town planners, urban administrators and the realities of the settlers' basic needs and resources. 相似文献
125.
126.
It has previously been suggested that the solar wind might terminate at distances of 5 AU to 20 AU from the Sun, and that the solar wind might be drastically slowed down by charge exchange and photoionization of interstellar hydrogen atoms which approach the Sun. However, recent satellite measurements of resonantly scattered Lyman alpha radiation, together with pulsar dispersion and Faraday rotation measures, imply very small values for the interstellar hydrogen density (0.05 cm−3) and magnetic field strength (3 μG). As a result, the solar wind is not expected to be slowed down by more than about 30% inside the termination distance, which is expected to be about 100 AU. 相似文献
127.
L. Neil Frazer 《Geophysical Journal International》1982,70(2):529-533
Summary New formulae are obtained for the displacement potentials and displacements due to a point source with moment tensor, and for a fault with prescribed slip. These formulae, unlike previous formulae, are invariant, i.e. they are valid in any coordinate system, not just Cartesian coordinates or orthogonal curvilinear coordinates.
Apart from their invariance, these formulae have other advantages: they are exceedingly simple; the expressions for P -motion are nearly the same as those for S -motion; and the separation of far field motion from final static displacement is automatic. 相似文献
Apart from their invariance, these formulae have other advantages: they are exceedingly simple; the expressions for P -motion are nearly the same as those for S -motion; and the separation of far field motion from final static displacement is automatic. 相似文献
128.
Special line shapes are derived fro the λ 1356 Å () transition of atomic oxygen from metastable () time-of-flight spectra produced by electron impact dissociative excitation of O2, CO2, CO, and NO, and they are compared with the broadened λ 1304 A resonance line shapes deduced by Poland and Lawrence (1973) from atomic oxygen absorption studies. The non-thermal line shapes for both airglow emission features are shown to have an effective width comparable to a 60,000 K thermal doppler line shape for an electron impact energy of 100eV. The variation of the effective line width with electron-impact energy from threshold to 300 eV is given. Since the effective line width of the resonance radiation produced by dissociative excitation is very large compared with the doppler absorption widths of the ambient O atoms at normal exospheric temperatures, the anomalously broadened resonance lines will propagate through a planetary atmosphere as though they were optically thin. Thus, electron-impact dissociation of CO and CO2 will contribute to the observed optically thin component of the λ 1304 Å emission in the upper atmospheres of Venus and Mars. However, the process cannot account for more than 10% of the observed optically thin emission because of the small magnitude of the excitation cross-section and the comparatively high-energy threshold for the process. The possibility that the source of the kinetically energetic ) atoms is the dissociative recombination of vibrationally excited CO2+ ions is discussed. 相似文献
129.
Neil S. Mancktelow 《Mathematical Geology》1981,13(6):507-521
Given a set of nondirectional orientation data (fold axes, lineations, dip and dip direction of bedding, universal stage readings of crystallographic axes, etc.),the best-fit line (point maximum),plane (great circle),or cone (small circle)can be determined by minimizing the sum of the squares of the angular residuals using a simplex convergence technique. Stereoplots of the angular deviation over the complete lower hemisphere for these distributions may also be generated when consideration of the constraint on the best-fit position is important; for example in comparing different data sets of the same structural element. The routines are available as a FORTRAN coded computer program. 相似文献
130.
An experimental study was undertaken to determine how the spectral and photometric properties of representative Martian areas are affected by fallout of atmospheric dust suspended during dust forms. A laboratory apparatus was used to simulate the uniform fallout and deposition of particles 1 to 5 μm in diameter. Spectral measurements from 0.4- to 1.2-μm wavelengths and photometric measurements at several wavelengths were made for a number of Mars-analog materials before and after deposition of 6 × 10?5 to 1.5 × 10?3 g/cm2 of simulated fallout. These results indicate that the spectral and photometric properties of Martian regions can be affected significantly even by minute amounts of fallout. For instance, the reflectance at 0.56 μm of an average dark area will increase by 35% after deposition of only 9 × 10?5 g/cm2, and by 70% after deposition of 1.5 × 10?4 g/cm2. Thus the fallout from even one dust storm season (~2 × 10?3 g/cm2) is sufficient to change significantly the spectral and photometric characteristics of the substrate material, if the fallout were ubiquitous over the surface and if no competing processes of dust removal from surface grains occured. 相似文献