全文获取类型
收费全文 | 1618篇 |
免费 | 65篇 |
国内免费 | 29篇 |
专业分类
测绘学 | 39篇 |
大气科学 | 176篇 |
地球物理 | 360篇 |
地质学 | 597篇 |
海洋学 | 131篇 |
天文学 | 248篇 |
综合类 | 4篇 |
自然地理 | 157篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 31篇 |
2020年 | 33篇 |
2019年 | 21篇 |
2018年 | 48篇 |
2017年 | 40篇 |
2016年 | 74篇 |
2015年 | 45篇 |
2014年 | 65篇 |
2013年 | 109篇 |
2012年 | 54篇 |
2011年 | 98篇 |
2010年 | 83篇 |
2009年 | 91篇 |
2008年 | 90篇 |
2007年 | 93篇 |
2006年 | 93篇 |
2005年 | 61篇 |
2004年 | 63篇 |
2003年 | 47篇 |
2002年 | 47篇 |
2001年 | 39篇 |
2000年 | 31篇 |
1999年 | 36篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 19篇 |
1995年 | 16篇 |
1994年 | 12篇 |
1993年 | 16篇 |
1992年 | 7篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有1712条查询结果,搜索用时 15 毫秒
91.
Charismatic wildlife can be difficult to manage due to the controversies they generate among stakeholders, which may be rooted in their symbolic meaning. Using construal-level theory, we coded the images of gray wolves mentioned by respondents to a national survey (n?=?621) and an issue public survey (n?=?447) as symbolic (abstract) or corporeal (concrete). We analyzed the relationship between these representations of wolves and several perceptions that may perpetuate social conflict. Most people thought of wolves abstractly, and abstract thoughts were associated with positive feelings toward wolves and agreement with existence beliefs regarding wolves. Concrete representations were associated with identifying as a gun or property rights advocate, hunter, or farmer/rancher. Given these disparate views of wolves, engaging stakeholders through collaborative processes designed to foster a shared understanding of this species, while addressing the concerns of those groups, could be useful in reducing conflict concerning wolf management. 相似文献
92.
Control of sediment dynamics by vegetation as a key function driving biogeomorphic succession within fluvial corridors 总被引:1,自引:0,他引:1
Dov Corenblit Johannes Steiger Angela M. Gurnell Eric Tabacchi Lydie Roques 《地球表面变化过程与地形》2009,34(13):1790-1810
Riparian vegetation responds to hydrogeomorphic disturbances and environmental changes and also controls these changes. Here, we propose that the control of sediment erosion and deposition by riparian vegetation is a key geomorphological and ecological (i.e. biogeomorphic) function within fluvial corridors. In a 3 year study, we investigated the correlations between riparian vegetation and hydrogeomorphic dynamics along a transverse gradient from the main channel to the floodplain of the River Tech, France. Sediment erosion and deposition rates varied significantly along the transverse gradient as a function of the vegetation biovolume intercepting water flow. These effects, combined with the extremely strong mechanical resistance of pioneer woody structures and strong resilience of pioneer labile herbaceous communities, Populus nigra and Salix spp., explain the propensity of biogeomorphic succession (i.e. the synergy between vegetation succession and landform construction) to progress between destructive floods. This geomorphological function newly identified as an ‘ecosystem function’ per se encompasses the coupling of habitat and landform creation, maintenance and change with fundamental ecosystem structural changes in space and in time. Three different biogeomorphic functions, all related to the concept of ecosystem engineering, were identified: (i) the function of pioneer herbaceous communities to retain fine sediment and diaspores in the exposed zones of the active tract near the water resource, facilitating recruitment of further herbaceous and Salicacea species; (ii) the function of woody vegetation to drive the construction of forested islands and floodplains; and (iii) the function of stabilised riparian forests to act as ‘diversity reservoirs’ which can support regeneration after destructive floods. Overall, this study based on empirical data points to the fundamental importance of sediment flow control by pioneer riparian vegetation in defining fluvial ecosystem and landform organisation in time and in space. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
93.
Irene Pundt Jean-Pierre Pommereau Celine Phillips Eric Lateltin 《Journal of Atmospheric Chemistry》1998,30(1):173-185
It has been suggested that iodine oxides, IOx, could play a significant role in the ozone destruction in the lower stratosphere. To investigate this suggestion, spectra from nine SAOZ uv-visible spectrometer balloon flights were examined for the IO absorption signature between 405 and 450 nm. IO was not detected, either at mid- or high latitude, in the morning or the evening, in summer or winter. An upper limit of 0.2 parts per trillion by volume (pptv) at 20 km and 0.1 pptv at 15 km at the 95% confidence level (2), was derived from the best measurements at 90° SZA at sunset and sunrise. Since a photochemical model shows that 70% of inorganic iodine should be in the form IO at that time, it is concluded that unless iodine chemistry is different from that assumed at the moment, the role of iodine in stratospheric ozone depletion is small. 相似文献
94.
Kais Aridhi Sabri Aridhi Mohamed Abdoullah Ould Bagga Saâdi Abdeljaouad Fouad Zargouni Eric Mercier 《Arabian Journal of Geosciences》2013,6(5):1591-1599
The imbrication’s area in northern Tunisia is the most external segment of Alpine range, where several associated folds types with thrust ramps are recognized within imbricate units beneath Numidian front slope. Their presence help to understand thrusting mechanisms installation through studied area. In fact, this zone was considered as a result of Paleogene gravitary slop (Kujawski (Ann Miner Géol Tunis (24):281, 1969); Caire (Ann Min Géol Tunis 26:87–110, 1973); Rouvier 1977), which is proved to be affected by major deep decollement, given rise to various structures, some are propagation folds, specific of foreland front, limited to this area, and those in more external position: Tunisian Atlas (Creusot et al. (C R Acad Sci Paris 314(Sér II):961–965, 1992); Ouali and Mercier (PII: S0191-8141(97):00048-5, 1997); Ouali 1984; Ahmadi et al. (J Struct Geol 28:721–728, 2006)). Various categories of fold ramps could be identified: frontal folds ramp NE–SW and others as lateral or oblique ramp with NW–SE trend (Aridhi et al. (C R Geosci 343:360–369, 2011)). The relation between various structures has been used as recognition tools of thrusting sequences and to propose a new deformation chronology. Delimited outcropping of these structures between two both parallel faults strikes with regional displacement, leads to interpret these faults as cogenetic tear faults of propagation thrusts; this fault separates two domains with different deformation styles from each other side. 相似文献
95.
RÉSUMÉLes modèles pluie–débit sont fortement utilisés dans la gestion des risques hydrologiques et la prévision des crues. Dans cette étude, nous présentons un modèle pluie–débit pour la prévision des débits horaires basé sur la technique des réseaux de neurones artificiels (RNA). Ce modèle a été développé et appliqué sur le bassin versant de l’Eure au Nord-Ouest de la France afin de dépasser les problèmes dus à la non-linéarité de la relation pluie–débit et à l’imprécision des données collectées. La création de ce modèle a nécessité plusieurs étapes pendant lesquelles nous avons pu déterminer les paramètres du modèle permettant la compréhension de la complexité hydrologique et la production des informations nécessaires à la prévision. Elles ont abouti à un modèle de réseau de neurones artificiels capable d’effectuer, en quelques secondes, des prévisions des crues efficaces jusqu’à un horizon de prévision de 48 h. Ces résultats confirment que les modèles RNA peuvent jouer un rôle important dans le domaine de la prévision car capables de modéliser la non-linéarité des relations pluie–débit rencontrées sur certains bassins hydrologiques.
Editor Z.W. Kundzewicz Associate editor E. Gargouri 相似文献
96.
This study maps the geographic extent of intermittent and seasonal snow cover in the western United States using thresholds of 2000–2010 average snow persistence derived from moderate resolution imaging spectroradiometer snow cover area data from 1 January to 3 July. Results show seasonal snow covers 13% of the region, and intermittent snow covers 25%. The lower elevation boundaries of intermittent and seasonal snow zones increase from north-west to south-east. Intermittent snow is primarily found where average winter land surface temperatures are above freezing, whereas seasonal snow is primarily where winter temperatures are below freezing. However, temperatures at the boundary between intermittent and seasonal snow exhibit high regional variability, with average winter seasonal snow zone temperatures above freezing in west coast mountain ranges. Snow cover extent at peak accumulation is most variable at the upper elevations of the intermittent snow zone, highlighting the sensitivity of this snow zone boundary to climate conditions. 相似文献
97.
Yingfeng?Zhang Guohong?ZhangEmail author Eric?A.?Hetland Xinjian?Shan Shaoyan?Wen Ronghu?Zuo 《Pure and Applied Geophysics》2016,173(4):1029-1038
The complete surface deformation of 2015 Mw 8.3 Illapel, Chile earthquake is obtained using SAR interferograms obtained for descending and ascending Sentinel-1 orbits. We find that the Illapel event is predominantly thrust, as expected for an earthquake on the interface between the Nazca and South America plates, with a slight right-lateral strike slip component. The maximum thrust-slip and right-lateral strike slip reach 8.3 and 1.5 m, respectively, both located at a depth of 8 km, northwest to the epicenter. The total estimated seismic moment is 3.28 × 1021 N.m, corresponding to a moment magnitude Mw 8.27. In our model, the rupture breaks all the way up to the sea-floor at the trench, which is consistent with the destructive tsunami following the earthquake. We also find the slip distribution correlates closely with previous estimates of interseismic locking distribution. We argue that positive coulomb stress changes caused by the Illapel earthquake may favor earthquakes on the extensional faults in this area. Finally, based on our inferred coseismic slip model and coulomb stress calculation, we envision that the subduction interface that last slipped in the 1922 Mw 8.4 Vallenar earthquake might be near the upper end of its seismic quiescence, and the earthquake potential in this region is urgent. 相似文献
98.
The stability of the Atlantic meridional overturning circulation (MOC) is investigated for various climate scenario runs, using data from the CMIP3 archive of coupled atmosphere-ocean models. Apart from atmospheric feedbacks, the sign of the salt flux into the Atlantic basin that is carried by the MOC determines whether the MOC is in the single or multiple equilibria regime. This salt advection feedback is analyzed by diagnosing the freshwater and salt budgets for the combined Atlantic and Arctic basins. Consistent with the finding that almost all coupled climate models recover from hosing experiments, it is found that most models feature a negative salt advection feedback in their pre-industrial climate: freshwater perturbations are damped by this feedback, excluding the existence of a stable off-state for the MOC. All models feature enhanced evaporation over the Atlantic basin in future climates, but for a moderate increase in radiative forcing (B1 and 2 CO2 scenarios), there is a decrease of the fresh water flux carried by the MOC into the Atlantic (the deficit is made up by increased fresh water transport by the gyre circulation). In this forcing regime the salt advection feedback becomes less negative: for three models from an ensemble of eight it is positive in a 2 CO2 climate, while two models feature a positive feedback in the pre-industrial climate. For even warmer climates (A1B-equilibrium and 4 CO2) the salt feedback becomes more negative (damping) again. It is shown that the decrease in northward fresh water transport at 34°S by the MOC (in B1-equilibrium and 2 CO2) is due to a reduction of the inflow of intermediate waters relative to thermocline waters, associated with a robust shoaling of the MOC in future, warmer climates. In A1B and 4 CO2 climates northward freshwater transport increases again. The MOC keeps shoaling, but both intermediate and thermocline water masses freshen. 相似文献
99.
Eric G. Blackman George B. Field 《Monthly notices of the Royal Astronomical Society》2008,386(3):1481-1486
The magnetic Reynolds number, R M , is defined as the product of a characteristic scale and associated flow speed divided by the microphysical magnetic diffusivity. For laminar flows, R M also approximates the ratio of advective to dissipative terms in the total magnetic energy equation, but for turbulent flows this latter ratio depends on the energy spectra and approaches unity in a steady state. To generalize for flows of arbitrary spectra we define an effective magnetic dissipation number, R M,e , as the ratio of the advection to microphysical dissipation terms in the total magnetic energy equation, incorporating the full spectrum of scales, arbitrary magnetic Prandtl numbers, and distinct pairs of inner and outer scales for magnetic and kinetic spectra. As expected, for a substantial parameter range R M,e ∼ O (1) ≪ R M . We also distinguish R M,e from where the latter is an effective magnetic Reynolds number for the mean magnetic field equation when a turbulent diffusivity is explicitly imposed as a closure. That R M,e and approach unity even if R M ≫ 1 highlights that, just as in hydrodynamic turbulence, energy dissipation of large-scale structures in turbulent flows via a cascade can be much faster than the dissipation of large-scale structures in laminar flows. This illustrates that the rate of energy dissipation by magnetic reconnection is much faster in turbulent flows, and much less sensitive to microphysical reconnection rates compared to laminar flows. 相似文献
100.
Ernest S. GLADNEY Elizabeth A. JONES Eric J. NICKELL Iwan ROELANDTS 《Geostandards and Geoanalytical Research》1990,14(2):209-359
Concentration data on up to 82 individual constituents in USGS Basalt BCR-1 have been collected from 1395 journal articles and technical reports. These data are summarized in consensus (mean) values with uncertainties expressed as ± one standard deviation. Mean values are also calculated as a function of analytical procedure and all raw data are given in the tables. Recommended values are proposed based upon data criteria used by NIST (National Institute of Standards and Technology, formerly the National Bureau of Standards or NBS). 相似文献