全文获取类型
收费全文 | 714篇 |
免费 | 43篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 57篇 |
地球物理 | 248篇 |
地质学 | 242篇 |
海洋学 | 62篇 |
天文学 | 82篇 |
综合类 | 1篇 |
自然地理 | 52篇 |
出版年
2023年 | 6篇 |
2021年 | 18篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 29篇 |
2013年 | 50篇 |
2012年 | 32篇 |
2011年 | 36篇 |
2010年 | 48篇 |
2009年 | 41篇 |
2008年 | 41篇 |
2007年 | 40篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 30篇 |
2003年 | 32篇 |
2002年 | 23篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1907年 | 1篇 |
排序方式: 共有765条查询结果,搜索用时 31 毫秒
181.
Marc Daignieres Vincent Courtillot Roger Bayer Paul Tapponnier 《Earth and Planetary Science Letters》1975,26(2):222-232
In Iceland tectonic activity in the neovolcanic zone leads to the formation of three kinds of parallel structures: open fissures, emissive fissures, and normal faults.This observation is used to built a kinematic model which is based on the superposition of lava flows generated from an active central belt of finite width. The results are in good agreement with the recent results in magnetism and tectonic observations of both subaerial and underwater active ridges. 相似文献
182.
Late Holocene volcanic activity at Ruapehu has been characterizedby the generation of small (<105 m3) to very large (>107 m3) lahars and repeated,small to medium (VEI 1-3) tephra-producing eruptions. The Onetapu Formation groupsall lahar deposits that accumulated during the last 2,000 years on the southeastern Ruapehu ring plain. The andesitic tephras are grouped within the Tufa Trig Formation and are intercalated within the laharic sequence. By correlating these two formations with new radiocarbon ages obtained on interbedded paleosols, we reconstruct a detailed volcanic history of Ruapehu for this period.Clast assemblages identified in the laharic sequences record thelithologies of synchronous tephras and rocks within the source region. These assemblages suggest a strong genetic link between the development of Crater Lake, the variation in eruptivestyles, and the production of lahars.Lahar-triggering mechanisms include: (1) flank collapse ofhydrothermally altered and unstable portions of the cone; (2) phreatic and phreatomagmatic eruptions favoring the generation of snow-rich slurries and hyperconcentrated stream flows; (3) suddenCrater Lake rim collapse, releasing large amounts of water inducing debris flows; and (4) eruptions that generate large volumes of tephra on snow-covered slopes, later remobilized by heavy rain.Two major lahars in the Onetapu sequence had a volume 4 × 107 m3, roughly 1 to 2 orders of magnitude larger than the 1953event leading to the Tangiwai disaster (151 casualties). One of these lahars crossed over a lowinterfluve currently separating the Whangaehu River from a stream feeding the Tongariro River,sometime since peat accumulated between AD 1400 and AD 1660. A repetition of such a large-scaleevent would have devastating consequences on the infrastructure, economy and environment withinthe distal areas of the two catchments. The 1995–1996 eruptions were a timely reminder ofthe hazards posed by the volcano. 相似文献
183.
184.
Introduction In recent years some big cities in China commonly build subways in central urban areas to improve crowded surface transportation, and the subways usually are large-scale group cavities composed by two parallel cavities. Construction of large-scale group cavities will certainly affect the design ground motion near the cavities, and further affect seismic safety of the existing build-ings nearby. So it is of significance to estimate this effect on seismic design of the buildings. H… 相似文献
185.
186.
利用波函数展开法,给出了地下圆形衬砌隧道对入射平面P波和SV波散射问题的一个级数解答,当衬砌与半空间介质相同时,该解答退化为文献中的无衬砌隧道的解答。级数解答为进一步定量研究隧道对入射平面P波和SV波的放大作用以及入射波长、入射角度、隧道直径和衬砌刚度等参数对隧道沿线地震动的影响奠定了理论基础。 相似文献
187.
The present paper reports recent improvements in sealed tube combustion technique used for the determination of N isotopic composition in various rocks characterized by low N contents (i.e. few ppm). Nitrogen is extracted from samples by combustion in quartz tubes sealed under vacuum. The nitrogen gas purified using Cu, CuO and CaO, is quantified as dinitrogen N2 by capacitance manometry in ultra-high vacuum line. Nitrogen isotopic analysis is performed on a triple-collector static vacuum mass spectrometer, allowing measurement of nanomole quantity of N2. Nitrogen amount and isotopic composition of the analytical blanks are low and describe Gaussian distribution with mean values of 0.65 ± 0.30 nmol N and − 3.7‰ ± 2.7‰, respectively (2σ). Systematic analyses of international and internal standards demonstrate that this technique provides accurate and precise results. The precision on N content and isotopic composition are better than ± 8% and ± 0.5‰ respectively, even for samples containing less than 2 ppm N. The sealed tube combustion technique is shown to apply successfully to rocks of various lithologies such as metagabbros, metaperidotites and altered basalts. It is thus suitable for studying oceanic crust in a perspective to better constrain N exchanges between Earth mantle and surface reservoirs. The investigation can also be extended to analysis of small size samples, particularly when little sample exists and when high spatial resolution is required. 相似文献
188.
189.
Vincent R. Eke Shaun Cole Carlos S. Frenk & J. Patrick Henry 《Monthly notices of the Royal Astronomical Society》1998,298(4):1145-1158
The evolution of the abundance of galaxy clusters depends sensitively on the value of the cosmological density parameter, Ω0 . Recent ASCA data are used to quantify this evolution as measured by the cluster X-ray temperature function. A χ2 minimization fit to the cumulative temperature function, as well as a maximum-likelihood estimate (which requires additional assumptions about cluster luminosities), leads to the estimate Ω0 ≈ 0.45 ± 0.25 (1σ statistical error). Various systematic uncertainties are considered, none of which significantly enhances the probability that Ω0 = 1. These conclusions hold for models with or without a cosmological constant, i.e., with Λ0 = 0 or Λ0 = 1 − Ω0 . The statistical uncertainties are at least as large as any of the individual systematic errors that have been considered here, suggesting that additional temperature measurements of distant clusters will allow an improvement in this estimate. An alternative method that uses the highest redshift clusters to place an upper limit on Ω0 is also presented and tentatively applied, with the result that Ω0 1 can be ruled out at the 98 per cent confidence level. Whilst this method does not require a well-defined statistical sample of distant clusters, there are still modelling uncertainties that preclude a firmer conclusion at this time. 相似文献
190.
Implications of ozone depletion for surface-water photochemistry: Sensitivity of clear lakes 总被引:1,自引:0,他引:1
Norman M. Scully Warwick F. Vincent David R. S. Lean William J. Cooper 《Aquatic Sciences - Research Across Boundaries》1997,59(3):260-274
Increased ultraviolet-B radiation (UV-B) in aquatic ecosystems brought about by stratospheric ozone depletion may result in
increased formation rates of photochemical reaction products in the surface waters of aquatic ecosystems. In this study, the
potential impact of increases in lower wave-length radiation on the formation of hydrogen peroxide (H2O2) and singlet oxygen (1O2) was modelled for lakes over a range of dissolved organic carbon (DOC) concentrations. The impact of increased UV-B radiation
on the production of carbon monoxide (CO) was also calculated for two humic stained systems. The relative increases of H2O2 and1O2 production were greater in the clear lakes (70% increase in photochemical reaction rates near the surface) than the coloured
systems (25%). Production of CO in the study sites also increased under depleted ozone conditions implying increased DOC losses
to the overlying atmosphere. 相似文献