全文获取类型
收费全文 | 938篇 |
免费 | 34篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 25篇 |
大气科学 | 50篇 |
地球物理 | 177篇 |
地质学 | 302篇 |
海洋学 | 86篇 |
天文学 | 181篇 |
综合类 | 4篇 |
自然地理 | 156篇 |
出版年
2021年 | 9篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 21篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 19篇 |
2014年 | 25篇 |
2013年 | 43篇 |
2012年 | 23篇 |
2011年 | 50篇 |
2010年 | 20篇 |
2009年 | 37篇 |
2008年 | 42篇 |
2007年 | 49篇 |
2006年 | 41篇 |
2005年 | 36篇 |
2004年 | 35篇 |
2003年 | 24篇 |
2002年 | 23篇 |
2001年 | 32篇 |
2000年 | 22篇 |
1999年 | 33篇 |
1998年 | 18篇 |
1997年 | 19篇 |
1996年 | 12篇 |
1994年 | 9篇 |
1993年 | 13篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1971年 | 6篇 |
1970年 | 7篇 |
排序方式: 共有981条查询结果,搜索用时 31 毫秒
921.
Renewed volcanic activity near Mammoth Lakes, California, in the form of dome-collapse pyroclastic density currents (PDCs)
from either a new eruption at Mammoth Mountain or the Inyo craters would pose a significant hazard to critical infrastructure
there. This paper compares the risk from PDC impact hazards upon selected critical infrastructure from: (1) a 100 m tall dacite
dome on Mammoth Mountain and (2) three 200 m tall rhyolite domes at the southern end of the Inyo craters. For each scenario,
maximum estimated dynamic pressure and velocity from two PDC volumes (106 and 107 m3) are modeled with the EXPLORIS PDC software (Toyos et al. Nat Hazards 41(1):99–112, 2007). Risk to critical infrastructure
from Mammoth Mountain PDCs would be much greater than the Inyo PDCs because of both location and the greater kinetic energy
of the Mammoth PDC material, providing comparative insight to planners should a real eruption at one location or the other
be forthcoming. 相似文献
922.
Often researchers position themselves in relation to race, age and gender, but the body is less often discussed as an actual 'instrument of research'. We aim to extend thinking on this point by reflecting on a project we conducted on migrant women and food in New Zealand. We present a vignette as an example of how we used our bodies as 'instruments of research' at a 'shared lunch' attended by new migrants from a range of different countries. At the lunch some combined on their plates spicy dishes such as kimch'i (fermented vegetables) and sweet dishes such as pavlova (a meringue dessert). For others this combination prompted feelings of disgust. We conclude that the body is a primary tool through which all interactions and emotions filter in accessing research subjects and their geographies. 相似文献
923.
ABSTRACT. Recent work on Asian ethnic minority immigrants to cities in the Anglophone Pacific Rim argues that their settlement patterns do not conform to those of earlier migrant streams. Instead of concentrating in high‐density, low‐quality, inner‐city housing, these new residents are moving directly to suburban areas where they form much less intensive concentrations—ethnoburbs—than has been typical of other culturally distinct migrant groups. We evaluate this thesis for Asian migrants in the Auckland metropolitan area, whose numbers more than quadrupled between 1991 and 2006. Their residential pattern is compared with that of Pacific Islanders also resident there, providing supporting evidence for the ethnoburb hypothesis. 相似文献
924.
Ron Johnston 《New Zealand geographer》2009,65(3):167-170
New Zealand Geographic is one of a number of geographical magazines published in the English‐speaking world that make little or no reference to work by academic geographers. It recently launched a New Zealand Geographic Trust to promote research into ‘New Zealand's life, culture and sciences’ and collaborated with four other publishers of geographical magazines to raise awareness of climate change: the work of academic geographers is again ignored. This exclusion of academic and school geography from such enterprises raises important issues regarding the discipline's public profile in New Zealand and suggests the need for greater public engagement activity by the country's geographers. 相似文献
925.
B. M. Gaensler † B. W. Stappers D. A. Frail D. A. Moffett ‡ S. Johnston S. Chatterjee 《Monthly notices of the Royal Astronomical Society》2000,318(1):58-66
We report on a sensitive survey for radio pulsar wind nebulae (PWN) towards 27 energetic and/or high-velocity pulsars. Observations were carried out at 1.4 GHz using the Very Large Array and the Australia Telescope Compact Array and utilized pulsar-gating to search for off-pulse emission. These observing parameters resulted in a considerably more sensitive search than previous surveys and could detect PWN over a much wider range of spatial scales (and hence ambient densities and pulsar velocities). However, no emission clearly corresponding to a PWN was discovered. Based on these non-detections we argue that the young and energetic pulsars in our sample have winds which are typical of young pulsars, but produce unobservable PWN because they reside in low-density ( n ∼0.003 cm−3 ) regions of the interstellar medium. However, non-detection of PWN around older and less energetic pulsars can only be explained if the radio luminosity of their winds is less than 10−5 of their spin-down luminosity, implying an efficiency at least an order of magnitude smaller than that seen for young pulsars. 相似文献
926.
Ross Kleinschmidt 《Marine pollution bulletin》2009,58(10):1539-1543
A study was initiated to establish the suitability of the macroalgae, Catenella nipae as an environmental surveillance monitor for radiopharmaceutical waste discharges to aquatic environments. A series of experiments were conducted to establish the radioactive iodine (131I) concentration factor, and uptake and depuration characteristics of C. nipae. The steady state concentration factor was estimated to be 630 ± 80 mL g−1, with an uptake half-time of 160 ± 20 min. Elimination of 131I was found to follow a two phase model, the first having a rapid elimination rate with a half-time of <1 min, followed by the second phase with a half-time of 3.2 days. Application of the Michaelis-Menton model allowed calculation of an estimate for activity concentration of 131I in environmental waters from C. nipae sampling devices in the Brisbane River estuary, Australia. The results suggest that C. nipae may be used as an environmental radioactive waste sentinel. 相似文献
927.
Large and growing environmental reservoirs of Deca-BDE present an emerging health risk for fish and marine mammals 总被引:2,自引:0,他引:2
Ross PS Couillard CM Ikonomou MG Johannessen SC Lebeuf M Macdonald RW Tomy GT 《Marine pollution bulletin》2009,58(1):7-10
Polybrominated diphenyl ethers (PBDEs) have been the subject of intense scientific and regulatory scrutiny during recent years. Of the three commercial forms (Penta, Octa and Deca) of PBDEs that have been widely used as flame retardants in textiles, furniture upholstery, plastics, and electronics, only Deca-BDE remains on the general market in North America, while a recent ruling of the European Court spells an impending end to its use in Europe. We review here highlights of aquatic research documenting the rapid emergence of PBDEs as a high priority environmental concern in Canada. PBDEs are being introduced in large quantities to the aquatic environment through sewage discharge and atmospheric deposition. In certain environmental compartments, the single congener BDE-209, the main ingredient in the Deca-BDE formulation, has surpassed the legacy PCBs and DDT as the top contaminant by concentration. Limited biomagnification of BDE-209 in aquatic food webs reflects its high log Kow and preferential partitioning into the particle phase. As a result, large environmental reservoirs of BDE-209 are being created in sediments, and these may present a long-term threat to biota: BDE-209 breaks down into more persistent, more bioaccumulative, more toxic, and more mobile PBDE congeners in the environment. 相似文献
928.
Pierre-Simon Ross James D.L. White Bernd Zimanowski Ralf Büttner 《Journal of Volcanology and Geothermal Research》2008
Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in unconsolidated material, no details are available regarding the structure of the disturbed debris between the explosion site and the surface. Field studies of diatreme deposits reveal cross-cutting, steep-sided zones of non-bedded volcaniclastic material that have been inferred to result from sedimentation of material transported by “debris jets” driven by explosions. In order to determine the general processes and deposit geometry resulting from discrete, explosive injections of entrained particles through a particulate host, we ran a series of analogue experiments. Specific volumes of compressed (0.5–2.5 MPa) air were released in bursts that drove gas-particle dispersions through a granular host. The air expanded into and entrained coloured particles in a small crucible before moving upward into the host (white particles). Each burst drove into the host an expanding cavity containing air and coloured particles. Total duration of each run, recorded with high-speed video, was approximately 0.5–1 s. The coloured beads sedimented into the transient cavity. This same behaviour was observed even in runs where there was no breaching of the surface, and no coloured beads ejected. A steep-sided body of coloured beads was left that is similar to the cross-cutting pipes observed in deposits filling real volcanic vents, in which cavity collapse can result not only from gas escape through a granular host as in the experiments, but also through condensation of water vapour. A key conclusion from these experiments is that the geometry of cross-cutting volcaniclastic deposits in volcanic vents is not directly informative of the geometry of the “intrusions” that formed them. An additional conclusion is that complex structures can form quickly from discrete events. 相似文献
929.
Evidence for fluid phase separation in high-grade ore zones at the Porgera gold deposit, Papua New Guinea 总被引:1,自引:0,他引:1
Coexisting, liquid-rich and vapor-rich primary fluid inclusions in quartz provide direct evidence for fluid phase separation
in high-grade quartz–roscoelite–gold veins and breccias from the Porgera alkalic-type gold deposit. Vapor-rich fluid inclusions
are CO2-rich, and sometimes contain liquid CO2 at room temperature. The close spatial and paragenetic relationship between these “boiling assemblage” fluid inclusions and
gold suggests that gold was precipitated by phase separation, at least locally. Additionally, the occurrence of carbonate
and sulfate minerals in high-grade veins (reflecting pH increase and oxidation of the boiled fluid) and the appearance of
hydrothermal breccias, are consistent with the process of fluid phase separation. Liquid CO2-bearing fluid inclusions are rare in near-surface epithermal deposits, and indicate that the Porgera vein system was formed
at greater depths and pressures (our estimates suggest pressures between 250 and 340 bars). It is suggested that alkalic-type
gold deposits may be distinguished from other epithermal deposit types by the more gaseous nature of the ore-forming fluids,
in addition to their association with alkalic magmas.
Received: 24 February 2000 / Accepted: 6 April 2000 相似文献
930.
Thilo Arlt Martin Kunz Jano Stolz Thomas Armbruster Ross J. Angel 《Contributions to Mineralogy and Petrology》2000,138(1):35-45
The P21/c clinopyroxene kanoite (ideally MnMgSi2O6) was studied as a function of pressure and temperature using powder X-ray diffraction, differential scanning calorimetry (DSC) and optical methods. The temperature of the P21/c to high-temperature (HT) C2/c transition ranges from 425?°C in endmember MnMgSi2O6 to 125?°C in natural samples with an aegirine component. Compiling pigeonite and clinoenstatite–clinoferrosilite literature data, the temperature of the transformation was found to decrease linearly with M2 cation size. A synchrotron powder diffraction study in a heated diamond-anvil cell (DAC) yielded compression and thermal expansion data for low kanoite of composition Mn1.2Mg0.4Fe0.4Si2O6. The high-pressure (HP) phase transition from P21/c to HPC2/c was reversed at 5.8 GPa at 417?°C. The high-temperature phase transition from P21/c to HTC2/c was rather indistinct and occurred at approximately 530?°C and 0.76 GPa. In a separate experiment, the HT transition was observed optically in a hydrothermal DAC between 0.0 and 0.4 GPa. The in-situP-T data of both experiments yielded an increase in transition temperature with increasing pressure (approx. 149?°C/GPa) and suggest a change in character of the transition from first order to continuous with increasing pressure. The data indicate that the HTC2/c and HPC2/c polymorphs are distinct phases with different stability fields. Since the high-temperature and the high-pressure polymorphs of kanoite were shown to be isotypic with other low-Ca clinopyroxenes such as the (Mg,Fe)SiO3 series, the conclusions we draw from this study are valid for all clinopyroxenes with small (<0.88 Å) M1 and M2 cation sizes. The petrologic implications of these conclusions for the occurrence of “clinoenstatite” in the Alpe Arami peridotite are discussed. 相似文献