全文获取类型
收费全文 | 3014篇 |
免费 | 138篇 |
国内免费 | 32篇 |
专业分类
测绘学 | 74篇 |
大气科学 | 235篇 |
地球物理 | 750篇 |
地质学 | 1012篇 |
海洋学 | 273篇 |
天文学 | 448篇 |
综合类 | 14篇 |
自然地理 | 378篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 53篇 |
2020年 | 51篇 |
2019年 | 59篇 |
2018年 | 66篇 |
2017年 | 67篇 |
2016年 | 89篇 |
2015年 | 90篇 |
2014年 | 92篇 |
2013年 | 196篇 |
2012年 | 139篇 |
2011年 | 185篇 |
2010年 | 143篇 |
2009年 | 167篇 |
2008年 | 157篇 |
2007年 | 163篇 |
2006年 | 146篇 |
2005年 | 127篇 |
2004年 | 124篇 |
2003年 | 109篇 |
2002年 | 101篇 |
2001年 | 71篇 |
2000年 | 66篇 |
1999年 | 59篇 |
1998年 | 55篇 |
1997年 | 38篇 |
1996年 | 45篇 |
1995年 | 30篇 |
1994年 | 34篇 |
1993年 | 33篇 |
1992年 | 28篇 |
1991年 | 26篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 28篇 |
1987年 | 30篇 |
1986年 | 24篇 |
1985年 | 32篇 |
1984年 | 33篇 |
1983年 | 23篇 |
1982年 | 27篇 |
1981年 | 25篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有3184条查询结果,搜索用时 186 毫秒
411.
412.
It is proposed that Saturn's electrostatic discharges (SED) might be generated in the planet's equatorial atmosphere, perhaps as lightning from a storm system. The 10h10m periodicity of the signal envelope duplicates that of Saturn's equatorial jet. The rings shield the atmosphere from solar EUV photons, and thereby substantially reduce the local ionospheric cutoff frequency to allow low-frequency SED to leak out. Many of the unusual properties of SED could be explained in terms of changes in the storm system, the relative spacecraft position in the beaming pattern of the source, local refraction of the signal by the highly disturbed ionosphere, and the influence of the ring particles on the highest frequency component of SED. A comparison of SED with planetary lightning on other planets shows that the two are similar in general character and some time behavior; the power output of SED may be higher than most planetary lightnings but that is unclear because of uncertainties in the measurements and variations in the signal's spectrum. Our simple discussion suggests that lightning could be a viable source for SED and that exotic ring mechanisms are not necessarily required. 相似文献
413.
414.
415.
Mark B. Boslough Thomas J. Ahrens Arthur C. Mitchell 《Geophysical Journal International》1986,84(3):475-489
Summary. Temperatures of CaAl2 Si2 O8 (anorthite glass) shocked to pressures between 48 and 117 GPa have been measured in the range from 2500 to 5600 K, using optical pyrometry techniques. The pressure dependence of the shock temperatures deviates significantly from predictions based on a single high-pressure phase. Either a variable specific heat, or the existence of three phase transitions, at pressures of about 55, 85 and 100 GPa and with transition energies of about 0.5 MJ kg−1 each (∼ 1.5 MJ kg−1 total) can explain the shock-temperature data. The proposed phase transition at 100 GPa can possibly be identified with the stishovite melting transition. Theoretical models of the time dependence of the thermal radiation from the shocked anorthite based on the geometry of the experiment and the absorptive properties of the shocked material yield good agreement with observations, indicating that it is not necessary to invoke intrinsic time dependences to explain the data in many cases. Observed time dependences were used to calculate absorption coefficients of the shocked material of from about 2 mm−1 to greater than 24 mm−1 – an increasing function of shock pressure. The assumption that the shocked material radiates as a black body is supported by the theoretical model, and by the close agreement between measured and calculated black body spectral radiance as a function of wavelength. 相似文献
416.
417.
Mark Cropper M. Barlow M. A. C. Perryman Keith Horne R. Bingham M. Page P. Guttridge A. Smith A. Peacock D. Walker P. Charles 《Monthly notices of the Royal Astronomical Society》2003,344(1):33-44
We describe a multi-order spectrograph concept suitable for 8-m class telescopes, using the intrinsic spectral resolution of superconducting tunnelling junction detectors to sort the spectral orders. The spectrograph works at low orders, 1–5 or 1–6, and provides spectral coverage with a resolving power of R ≃ 8000 from the atmospheric cut-off at 320 nm to the long-wavelength end of the infrared H or K band at 1800 nm or 2400 nm. We calculate that the spectrograph would provide substantial throughput and wavelength coverage, together with high time resolution and sufficient dynamic range. The concept uses currently available technology, or technologies with short development horizons, restricting the spatial sampling to two linear arrays; however, an upgrade path to provide more spatial sampling is identified. All of the other challenging aspects of the concept – the cryogenics, thermal baffling and magnetic field biasing – are identified as being feasible. 相似文献
418.
Wyatt Mark C. Holland Wayne S. Greaves Jane S. Dent William R. F. 《Earth, Moon, and Planets》2003,92(1-4):423-434
Debris disks are found around some 15% of main sequencestars and their dust is thought to be continuallyreplenished in collisions between planetesimals inextrasolar Kuiper belts.While they were discovered in 1984 by IRAS, it is onlywith more recent imaging that their true nature has beenrevealed. This paper discusses recent debris disk images andtheir impact on our understanding of extrasolar systems.Importantly these images confirm the extrasolar Kuiper belthypothesis for most (but not all) debris diskcandidates and show that the planetesimals within thesedisks must have grown to at least a few km.Asymmetries in imaged disk structures also provide informationabout the planetary systems orbiting inside these planetesimalbelts. The impact of debris disk studies on our understandingof the evolution of our own Kuiper belt, as well as theirpotential to solve puzzles such as the origin of the missingmass and the outer edge of the Kuiper belt, is alsodiscussed. 相似文献
419.
420.
Accepted practice dictates that waterflooding of gas reservoirs should commence, if ever, only when the reservoir pressure has declined to the minimum production pressure. Analytical proof of this hypothesis has yet to appear in the literature however. This paper considers a model for a gas-water reservoir with a variable production rate and enhanced recovery with waterflooding and, using an initial dynamic programming approach, confirms the above hypothesis. 相似文献