全文获取类型
收费全文 | 1156篇 |
免费 | 94篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 7篇 |
地球物理 | 345篇 |
地质学 | 724篇 |
海洋学 | 62篇 |
天文学 | 12篇 |
综合类 | 9篇 |
自然地理 | 103篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 17篇 |
2018年 | 15篇 |
2017年 | 27篇 |
2016年 | 61篇 |
2015年 | 51篇 |
2014年 | 63篇 |
2013年 | 241篇 |
2012年 | 41篇 |
2011年 | 50篇 |
2010年 | 38篇 |
2009年 | 46篇 |
2008年 | 75篇 |
2007年 | 44篇 |
2006年 | 62篇 |
2005年 | 97篇 |
2004年 | 73篇 |
2003年 | 62篇 |
2002年 | 68篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 20篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 2篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1273条查询结果,搜索用时 531 毫秒
191.
Nancy Pérez-Morga Thomas Kretzschmar Tereza Cavazos Stephen V. Smith Francisco Munoz-Arriola 《Geofísica Internacional》2013,52(3):277-291
Extreme wet and dry years (± 1 standard deviation, respectively), as well as the top 95 percentile (P95) of daily precipitation events, derived from tropical cyclone (TC) and nontropical cyclone (NTC) rainfall, were analyzed in coastal river basins in Southern Oaxaca, Mexico (Río Verde, Río Tehuantepec, and the Southern Coast). The study is based on daily precipitation records from 47 quality-controlled stations for the 1961 to 1990 period and TC data for the Eastern Tropical Pacific (EPAC). The aim of this study was to evaluate extreme (dry and wet) trends in the annual contribution of daily P95 precipitation events and to determine the relationship of summer precipitation with El Niño Southern Oscillation (ENSO) and the Pacifical Decadal Oscillation (PDO). A regionalization based on a rotated principal component analysis (PCA) was used to produce four precipitation regions in the coastal river basins. A significant negative correlation (significance at the 95% level) was only found with ONI in rainfall Region 3, nearest to the Gulf of Tehuantepec. Wet years, mainly linked to TC-derived P95 precipitation events, were associated with SST anomalies (≥?0.6°C) similar to weak La Niña and Neutral cool conditions, while dry years were associated with SST positive anomalies similar to Neutral warm conditions (≤?0.5°C). The largest contribution of extreme P95 precipitation derived from TCs to the annual precipitation was observed in Region 3. A significant upward trend in the contribution of TC-derived precipitation to the annual precipitation was found only in Region 1, low Río Verde. 相似文献
192.
Vladimir Sabinin 《Geofísica Internacional》2013,52(4):311-320
New computational techniques of QVOA analysis (Quality factor Versus Offset and Azimuth) for fracture characterization are developed. The techniques are applied to synthetic surface data of reflection with noise. 相似文献
193.
Global warming is likely modifying the hydrological cycle of forested watersheds. This report set as objectives to: a) assess the hydrological variables interception loss, I, potential and actual evapo-transpiration, E, Et, runoff, Q, and soil moisture content, θ; b) evaluate whether these variables are presenting consistent trends or oscillations that can be associated to global warming or climate variability; and c) relate θ to the number of wildfires and the burned area in Durango, Mexico. A mass balance approach estimated daily variables of the water cycle using sub-models for I and Et to calculate Q and θ for a time series from 1945 to 2007. Regression and auto-regressive and moving averaging (ARIMA) techniques evaluated the statistical significance of trends. The cumulative standardized z value magnified and ARIMA models projected statistically similar monthly and annual time series data of all variables of the water cycle. Regression analysis and ARIMA models showed monthly and annual P, I, E, and Et, Q, and θ do not follow consistent up or downward linear tendencies over time with statistical significance; they rather follow oscillations that could be adequately predicted by ARIMA models (r2 ≥ 0.70). There was a consistent statistical association (p ≤ 0.05) of θ with the number of wildfires and the area burned regardless of the different spatial scales used in evaluating these variables. The analysis shows seasonal variability is increasing over time as magnifying pulses of dryness and wetness, which may be the response of the hydrological cycle to climate change. Further research must center on using longer time series data, testing seasonal variability with additional statistical analysis, and incorporating new variables in the analysis. 相似文献
194.
Sergio Martínez-Trinidad Gilberto Hernández Silva Juventino Martínez Reyes Gregorio Solorio Munguía Sara Solís Valdez Martha Elena Ramírez Islas Rocío García Martínez 《Geofísica Internacional》2013,52(1):43-58
Deficient management of cinnabar mining left the San Joaquín region with high concentrations of mercury in its soils (2.4 – 4164 mg kg-1). Numerous cinnabar mines have contributed to the dispersion of mercury into agricultural (0.5 –314 mg kg-1) and forest (0.2 – 69 mg kg-1) soils. Sediments are a natural means of transportation for mercury, causing its spreading, especially in areas near mine entrances (0.6 – 687 mg kg-1). The nearness of maize crops to mines favors mercury accumulation in the different plant structures, such as roots, stems, leaves, and grain (0.04 – 8.2 mg kg-1); these being related to mercury volatilization and accumulation in soils. Mercury vapor present in the settlements could indicate a constant volatilization from lands and soils (22 – 153 ng m-3). The mercury levels found in the soils, in maize grain, and in the air resulted greater than the standards reported by the Official Mexican Norm (NOM) and the World Health Organization (WHO). Mercury in rainwater is due mainly to the presence of suspended atmospheric particles, later deposited on the surface (1.5 – 339 μg |-1). Mercury dissolution was found in the drinking water (10 – 170 ng |-1), with concentrations below those established by the NOM and the WHO. The contamination existing in the San Joaquín region does not reach the levels of the world’s greatest mercury producers: Almaden (Spain) and Idrija (Slovenia). It is, however, like that found in other important second degree world producers such as Guizhou (China). The population of San Joaquín, as well as its surrounding environment, are constantly exposed to mercury contamination, thus making a long term monitoring necessary to determine its effects, especially to people. 相似文献
195.
Luis M. Alva-Valdivia María de la Luz Rivas-Sánchez Jesús Arenas-Alatorre Avto Goguitchaishvili Omar Ferreira Lopes 《Geofísica Internacional》2013,52(2):93-110
Very fine samples from the mineralized zones of the Jacupiranga complex at the Cajati mine were selected for crystallographic identification of Ti-magnesioferrite (TMf) nanostructures embedded in titanomagnetite (TM) using high-resolution transmission electron microscopy (TEM). A magnetic concentrate obtained of pyroxenite samples (sites 4 to 7) was reduced and divided into fractions of distinct range sizes: 26±2 μm, 19±1 μm, 13±1 μm, 9±1 μm, 6±1 μm and 6-0.1 μm. The mineralized samples of carbonatite and pyroxenite were characterized by X-ray diffraction, transmitted and reflected light microscope, and scanning electron microscope with multielemental analysis. The finest magnetic concentrate sample (MC6) was analyzed under high-resolution transmitted electron microscopy (TEM) and high angle annular dark field and Raman spectroscopy. Magnetic properties were measured for the distinct granulometric fractions, showing drastic changes when grain sizes go beyond the frontier from micro to nanometer sizes. Frequency-dependent magnetic susceptibility percentage (÷fd%) report higher values (10.2%) for the finer fractions (6±1 μm and 6-0.1 μm) attributed to dominant fractions of superparamagnetic particles. Nanometer and < 6 μm grain size TMf in TM particles require a magnetic field up to 249 mT to reach saturation during the isothermal remanent magnetization experiment. Coercivity and remanent magnetization of these samples increase when the particle size decreases, probably due to parallel coupling effects. Magnetic susceptibility versus temperature experiments were conducted two times on the same (< 35 nm) sample, showing that the repetition during the second heating is probably due to the formation of new TMf nanoparticles and growth of those already present during the first heating process. 相似文献
196.
Cecilia Weidmann Silvana Spagnotto Orlando Álvarez Marcos Sánchez Federico Lince Klinger Mario Giménez Patricia Martínez 《Geofísica Internacional》2013,52(3):197-208
Based on terrestrial gravity data, in this paper we prepared a map of Bouguer anomalies, which was filtered to separate shallow and deep gravity sources. Based on a density model and gravimetric inversion techniques, the discontinuous crust-mantle boundary and the top of crystalline basement were modeled. Subsequently, the equivalent elastic thickness (Te) was evaluated, considering information from the crust-mantle discontinuity and topographic load, finding high Te values in the eastern Andean foothills and west of the Velasco range. These results are consistent with the positive isostatic and residual Bouguer anomaly values, which suggest the presence of high-density rocks in the mid-to upper crust. In addition, petrographic and geochemical analysis conducted in surface outcrops suggest a mantle origin. 相似文献
197.
Résumé Le modèle proposé est un générateur stochastique d'averses couplé à un modèle empirique de calcul de leurs érosivités, calé à une série pluviographique de 15 ans d'observations. Notre objectif est de développer une démarche probabiliste, qui permettrait d'étudier les conséquences érosives des pluies dans le temps, en cumulant l'érosivité consécutive des pluies simulées durant plusieurs années, supposée proportionnelle à la dégradation des sols, ou au transport solide en suspension sur la même période. Cette génération peut en effet se faire sur plusieurs années calendaires, et nous permettrait de ce fait d'éviter d'être limité par la taille des échantillons. L'ensemble pouvant être utilisé en mode opérationnel, pour reconstituer de très longus séries d'épisodes pluvieux dans l'objectif d'étudier le cumul de leur érosivité dans le temps. Cette démarche ne contredit pas les approches expérimentales, qui ont une réalité concrète de terrain, bien au contraire elle les conforte et permet d'avancer davantage dans la réflexion posée par la problématique de l'érosion hydrique. 相似文献
198.
Ernest Amoussou Yves Tramblay Henri S.V. Totin Gil Mahé Pierre Camberlin 《水文科学杂志》2013,58(11):2060-2071
RésuméLes inondations des dernières années en Afrique de l’Ouest rendent nécessaire la prévision hydrologique pour réduire la vulnérabilité des populations. Nous avons étudié la dynamique des crues dans le bassin du Mono en amont du barrage de Nangbéto (Togo et Bénin) par des méthodes statistiques et déterministes. L’augmentation des précipitations au cours de la décennie 1990 et la mise en eau du barrage de Nangbéto en 1988 ont modifié le régime du Mono, dont les débits d’étiages ont augmenté. Les débits entrants et sortants du barrage sont équivalents, même lors des crues. Les maximums annuels des débits entrants peuvent être modélisés par une distribution des valeurs extrêmes (GEV) de type Fréchet, tandis que ceux des débits sortants, suivent une loi GEV de type Weibull (bornée). Le mécanisme dominant de génération des crues dans le bassin est la montée progressive des eaux associée à l’augmentation de la saturation des sols. L’analyse des débits de crue entre 1988 et 2010 n’a pas montré d’augmentation de la magnitude ou de la fréquence des crues. Le modèle GR4J reproduit bien les débits de crues en période calage, mais ces critères de performance se dégradent lorsque l’on s’en éloigne. Dans ces conditions, l’utilisation de ce modèle pour évaluer les risques futurs de crues serait hasardeuse et il est nécessaire d’envisager d’autres types d’approches. 相似文献
199.
《水文科学杂志》2013,58(2)
Abstract Abstract The Chronology of British Hydrological Events (CBHE) has been created as an on-line information resource (http://www.dundee.ac.uk/geography/cbhe/) in order to enhance access to and use of historical facts pertaining to British hydrological phenomena. Its scope covers floods, droughts and all other notable historical phenomena of hydrological interest. This paper sets out the technical means by which the CBHE has been created, explains the benefits to hydrologists in creating such a facility, and illustrates its utility with a number of examples. Benefits include hydrological risk assessments, historical studies of individual events and objectives in environmental education. The scope for establishing comparable national chronologies for other countries is identified, along with prospects for enhancing the utility of such systems with additional functionality such as links to on-line gazetteers and maps. 相似文献
200.
《水文科学杂志》2013,58(4)
Abstract Abstract In the first part of this study, theoretical analyses showed that the Gumbel distribution is quite unlikely to apply to hydrological extremes and that the extreme value distribution of type II (EV2) is a more consistent choice. Based on these theoretical analyses, an extensive empirical investigation is performed using a collection of 169 of the longest available rainfall records worldwide, each having 100–154 years of data. This verifies the theoretical results. In addition, it shows that the shape parameter of the EV2 distribution is constant for all examined geographical zones (Europe and North America), with value κ = 0.15. This simplifies the fitting and the general mathematical handling of the distribution, which become as simple as those of the Gumbel distribution. 相似文献