全文获取类型
收费全文 | 607篇 |
免费 | 29篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 45篇 |
地球物理 | 149篇 |
地质学 | 210篇 |
海洋学 | 71篇 |
天文学 | 81篇 |
综合类 | 7篇 |
自然地理 | 61篇 |
出版年
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 14篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 21篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 38篇 |
2012年 | 21篇 |
2011年 | 34篇 |
2010年 | 29篇 |
2009年 | 37篇 |
2008年 | 19篇 |
2007年 | 29篇 |
2006年 | 28篇 |
2005年 | 17篇 |
2004年 | 14篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 12篇 |
1974年 | 6篇 |
1973年 | 8篇 |
1969年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有641条查询结果,搜索用时 15 毫秒
171.
In contrast to local perceptions, the impact on the local Galápagos artisanal fishery of the 16 January 2001 grounding of the Jessica and subsequent oil spill was relatively minor. No significant changes in fishing effort, total fishing catches or catch-per-unit effort were detected after the spill based on analyses of fisheries monitoring data. Nevertheless, large boats tended to move away from sites near the path of the spill following the grounding in 2001, with no fishing recorded from the oil-affected regions of Floreana and southern Isabela in February 2001. The total fishing effort of small boats operating from the Jessica-grounding island of San Cristóbal also declined immediately after the spill, probably in part because such boats were used in clean up operations. During 2001, prices paid to fishers remained stable at levels higher than in 2000, with the notable anomaly that prices fell precipitously to 30% of previous levels during a 1-2 week period in early February 2001. Fish exports remained at similar levels for the years 2000 and 2001; however, as in the previous year, little fish product was exported from Galápagos in the month following the spill, with most fish product dried and stored for up to two months prior to transport to the continent. 相似文献
172.
Dan McKenzie Andreas Stracke Francis Albarède R.Keith O’Nions 《Geochimica et cosmochimica acta》2004,68(12):2699-2724
A new method has been developed to separate the compositional variations in ocean island basalts into those that result from variations in source composition and from the melting process itself. The approach depends on correlations between isotope ratios, which can only come from source inhomogeneities, and elemental concentrations. Analysis of three data sets shows that the inhomogeneities beneath Theistareykir, in NE Iceland, Kilauea and Pitcairn can be produced by subduction of oceanic islands and volcanic ridges. The thicknesses of the lithosphere on which such islands were constructed and potential temperatures of the plumes that produced them can be estimated from the geochemical observations. Model ages are harder to determine, though simple assumptions give about 400 Ma for the Theistareykir source and 1.2 Ga for Kilauea. The model may also provide a physical explanation for the commonly used isotopic classification of ocean island basalts, with the isotopic composition changing from HIMU through EMII to EMI as the melt fraction increases. These results have been obtained from a small number of data sets obtained from ocean island basalts erupted in small areas during short time intervals. More such observations are needed to discover whether geochemical observations from other islands are consistent with the same model. 相似文献
173.
Francis Amédro Hugues Accarie et Francis Robaszynski 《Eclogae Geologicae Helvetiae》2005,98(2):151-167
Resume. Deux coupes de la Formation Bahloul en Tunisie centrale ont livré plus de 250 ammonites qui fondent une zonation en quatre
termes allant du Cénomanien terminal (Zones à Metoicoceras geslinianum et à Pseudaspidoceras pseudonodosoides) au Turonien basal (Zones à Watinoceras spp et à Pseudaspidoceras flexuosum). La position de la limite Cénomanien-Turonien (C-T) étant définie par l’apparition de Watinoceras spp, cette limite est placée à 0,60m près dans la localité-type de la Formation à l’Oued Bahloul. Sur les deux coupes étudiées
des mesures du carbone isotopique ont mis en évidence quatre événements – ou pics en δ13C – formant des lignes temporelles considérées comme synchrones dans la région considérée. L’événement δ13C indexé III, d’age encore cénomanien, est le plus proche de la limite C-T. Un événement biologique relatif à l’apparition
de ?filaments? – ou microlamellibranches pélagiques – toujours cénomanien, est encore plus proche de la limite C-T. Enfin,
une comparaison est tentée avec les Marnes à Plenus d’Eastbourne (UK) et avec le stratotype de la limite C-T à Pueblo (USA).
Manuscrit re?u le 15 octobre, 2004 Révision acceptée le 2 février, 2005 相似文献
174.
Toshihiko Ohnuki Takahiro Yoshida Takuo Ozaki Mohamad Samadfam Naofumi Kozai Kunio Yubuta Toshiaki Mitsugashira Takeshi Kasama Arokiasamy J. Francis 《Chemical Geology》2005,220(3-4):237-243
We assessed the accumulation of uranium (VI) by a bacterium, Bacillus subtilis, suspended in a slurry of kaolinite clay, to elucidate the role of microbes on the mobility of U(VI). Various mixtures of bacteria and the koalinite were exposed to solutions of 8 × 10− 6 M- and 4 × 10− 4 M-U(VI) in 0.01 M NaCl at pH 4.7. After 48 h, the mixtures were separated from the solutions by centrifugation, and treated with a 1 M CH3COOK for 24 h to determine the associations of U within the mixture. The mixture exposed to 4 × 10− 4 M U was analyzed by transmission electron microscope (TEM) equipped with EDS. The accumulation of U by the mixture increased with an increase in the amount of B. subtilis cells present at both U concentrations. Treatment of kaolinite with CH3COOK, removed approximately 80% of the associated uranium. However, in the presence of B. subtilis the amount of U removed was much less. TEM–EDS analysis confirmed that most of the U removed from solution was associated with B. subtilis. XANES analysis of the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both revealed that it was present as U(VI). These results suggest that the bacteria have a higher affinity for U than the kaolinite clay mineral under the experimental conditions tested, and that they can immobilize significant amount of uranium. 相似文献
175.
Robert A Francis 《Area》2006,38(4):453-464
Riparian vegetation dynamics are regarded as being driven by allogenic hydrogeomorphological factors, with autogenic (plant-induced) influences becoming more important as landform stability is achieved. Autogenic processes, however, may have a substantial influence on both plant dynamics and the river environment from the earliest stages of plant establishment. Various aspects of both allogenic and autogenic processes in riparian vegetation dynamics are discussed here; in particular how plants may promote bank stability and sedimentation, and river island development. Riparian restoration often fails to incorporate autogenic processes, thereby restricting the re-establishment of natural functioning, and further interdisciplinary work is needed to address this. 相似文献
176.
177.
Summary The west coast of the Indian peninsula receives very heavy rainfall during the summer Monsoon (June–September) season with
average rainfall over some parts exceeding 250 cm. Heavy rainfall events with rainfall more than 15 cm day−1 at one or more stations along the west coast of India occur frequently and cause considerable damage. A special observational
programme, Arabian Sea Monsoon Experiment, was carried out during the monsoon season of 2002 to study these events. The spatial
and temporal distributions of intense rainfall events, presented here, were used for the planning of this observational campaign.
The present study using daily rainfall data for summer monsoon season of 37 years (1951–1987) shows that the probability of
getting intense rainfall is the maximum between 14° N–16° N and near 19° N. The probability of occurrence of these intense
rainfall events is high from mid June to mid August, with a dip in early July. It has been believed for a long time that offshore
troughs and vortices are responsible for these intense rainfall events. However, analysis of the characteristics of cloud
systems associated with the intense rainfall events during 1985–1988 using very high resolution brightness temperature data
from INSAT-IB satellite shows that the cloud systems during these events are characterized by large spatial scales and high cloud tops.
Further study using daily satellite derived outgoing longwave radiation (OLR) data over a longer period (1975–1998) shows
that, most of these events (about 62%) are associated with systems organized on synoptic and larger scales. We find that most
of the offshore convective systems responsible for intense rainfall along the west coast of India are linked to the atmospheric
conditions over equatorial Indian Ocean. 相似文献
178.
Cycling of methane (CH4) in Tomales Bay, a 28-km2 temperature estuary in northern California with relatively low inputs of organic carbon, was studied over a 1-yr period. Water column CH4 concentrations showed spatial and temporal variability (range=8–100 nM), and were supersaturated with respect to the atmosphere by a factor of 2–37. Rates of net water column CH4 production-oxidation were determined by in situ experiments, and were not found to be significantly different from zero. Fluxes across the sediment-water interface, determined by direct measurement using benthic chambers, varied from ?0.1 μmol m?2 d?1 to +16 μmol m?2 d?1 (positive fluxes into water). Methane concentrations in the two perennial creeks feeding the bay varied annually (140–950 nM); these creeks were a significant CH4 source to the bay during winter. In addition, mass-balance calculations indicate a significant additional inter CH4 source, which is hypothesized to result from storm-related runoff from dairy farms adjacent to the bay. Systemwide CH4 budgets of the 16-km2 inner bay indicate benthic production (110 mol d?1) and atmospheric evasion (110 mol d?1) dominated during summer, while atmospheric evasion (160 mol d?1) and runoff from dairy farms (90 mol d?1) dominated during winter. 相似文献
179.
S. J. Watkins A. S. Bhattal H. M. J. Boffin N. Francis & A. P. Whitworth 《Monthly notices of the Royal Astronomical Society》1998,300(4):1214-1224
It is expected that an average protostar will undergo at least one impulsive interaction with a neighbouring protostar whilst a large fraction of its mass is still in a massive, extended disc. If protostars are formed individually within a cluster before falling together and interacting, there should be no preferred orientation for such interactions. As star formation within clusters is believed to be coeval, it is probable that, during interactions, both protostars possess massive, extended discs. We have used an SPH code to carry out a series of simulations of non-coplanar disc–disc interactions. We find that non-coplanar interactions trigger gravitational instabilities in the discs, which may then fragment to form new companions to the existing stars. (This is different from coplanar interactions, in which most of the new companion stars form after material in the discs has been swept up into a shock layer, and this then fragments.) The original stars may also capture each other, leading to the formation of a small- N cluster. If every star undergoes a randomly oriented disc–disc interaction, then the outcome will be the birth of many new stars and substellar objects. Approximately two-thirds of the stars will end up in multiple systems. 相似文献
180.