全文获取类型
收费全文 | 435篇 |
免费 | 19篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 32篇 |
地球物理 | 153篇 |
地质学 | 164篇 |
海洋学 | 35篇 |
天文学 | 50篇 |
综合类 | 1篇 |
自然地理 | 16篇 |
出版年
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 15篇 |
2012年 | 7篇 |
2011年 | 18篇 |
2010年 | 16篇 |
2009年 | 24篇 |
2008年 | 24篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 18篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有459条查询结果,搜索用时 31 毫秒
161.
Origin and formation pathways of kerogen-like organic matter in recent sediments off the Danube delta (northwestern Black Sea) 总被引:1,自引:0,他引:1
Anouk Garcette-Lepecq Sylvie Derenne Claude Largeau Ioanna Bouloubassi Alain Saliot 《Organic Geochemistry》2000,31(12):204
The chemical structure, source(s), and formation pathway(s) of kerogen-like organic matter (KL) were investigated in recent sediments from the northwestern Black Sea, off the Danube delta. Three sections from a sediment core collected at the mouth of the Sulina branch of the delta, under an oxic water column, were examined: S0 (0–0.5 cm bsf), S10 (10–13 cm bsf), and S20 (20–25 cm bsf). The bulk geochemical features of these sediments (total organic carbon, organic C/N atomic ratio, δ13Corg) were determined. Thereafter, KL was isolated from the samples, as the insoluble residue obtained after HF/HCl treatment. KL chemical composition was investigated via spectroscopic (FTIR, solid state 13C and 15N NMR) and pyrolytic (Curie point pyrolysis–gas chromatography–mass spectrometry) methods, and the morphological features were examined by scanning and transmission electron microscopy. Similar morphological features and chemical composition were observed for the three KLs and they suggested that the selective preservation of land-plant derived material as well as of resistant aliphatic biomacromolecules (probably derived from cell walls of freshwater microalgae) was the main process involved in KL formation. Besides, some melanoidin-type macromolecules (formed via the degradation-recondensation of products mainly derived from proteinaceous material) and/or some encapsulated proteins also contributed to the KL chemical structure. 相似文献
162.
Thanh Thuy Nguyen Tu Sylvie Derenne Claude Largeau Andr Mariotti Herv Bocherens Denise Pons 《Organic Geochemistry》2000,31(12):25
The lipid fraction extracted from uninfected shoots of a fossil conifer, Frenelopsis alata, was analysed by gas-chromatography–mass-spectrometry, and compared with shoots of the same conifer infected by extinct epiphyllous fungi, so as to study the effects of fungal infection on the chemical composition of extracts from higher plant remains. The extracts from the uninfected shoots appeared to be composed of (i) common constituents of higher plant lipids such as n-alkanes and fatty acids, (ii) elemental sulphur, and (iii) substantial amounts of terpenoids characteristic of conifers, such as cadalene, beyerane, dehydroabietane and related compounds. Comparison of this extract with that of fungal-infected shoots revealed, in addition to the aforementioned compounds, the presence of substantial amounts of hydroxysuccinic acid and functionalised benzoic compounds that were interpreted as degradation products of lignin by fungi. This study afforded preliminary indications of the composition of extracts from higher plant remains infected by fungi. 相似文献
163.
164.
Francis Sondag Jean Loup Guyot Jean Sbastien Moquet Alain Laraque Georges Adele Grard Cochonneau Jean Claude Doudou Christelle Lagane Philippe Vauchel 《水文研究》2010,24(11):1433-1445
This study presents the data collected within the framework of an Observatory of Research in Environment on the Amazonian Basin—the ORE HYBAM. It relates to the dissolved and solid loads of the two main rivers of French Guiana, the Maroni and Oyapock rivers, running on the Guiana Shield and draining respectively 64 230 and 24 630 km2. The low coefficient of variation of the average annual flows of the two rivers indicates an inter‐annual hydrological stability probably related to the immediate vicinity of the Atlantic Ocean. The sedimentary load is mainly composed of quartz and kaolinite. The total suspended solid (TSS) concentrations are among the world's lowest values; they range from 1 to 130 mg l−1 during the hydrological cycle, with averages of 22 and 12 mg l−1, for the Maroni and Oyapock rivers, respectively. The seasonal variability of these values is significantly higher than that of hydrologic flows, but without simple relationship with the discharge. Water chemical composition of the two rivers indicates a very weak mineralization, very similar to that found in the Amazonian rivers running on the Brazilian and Guianese shields, and in the Congo River and its tributaries in the Central African Shield. Seasonal variations are observed in both basins; they correspond to higher concentrations during low water stage (from October to February) and to more diluted water during the flood, from April to July. A signature enriched in Cl− is present at the Saut Maripa station on the Oyapock River indicating a more marked influence of the trade winds in this basin. The computation of atmospheric contributions to ions budget indicated a weak contribution for Ca2+ and Mg2+, which originates mainly from water‐rock interactions in both stations, while more than half of Na+ is derived from atmospheric inputs. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
165.
Volcanic islands, being characterized by highly porous basaltic/andesitic lava flows and pyroclastic deposits, are subject
to important chemical weathering by subsurface waters. Moreover, such subsurface weathering is impacted by hydrothermal springs
in both active and non-active volcanic areas, thus increasing dissolved load concentrations. Here, we focus on the subsurface
water chemistry in the volcanic islands of the Lesser Antilles and Réunion and on the origin of these subsurface flows. We
are able, through the use of various isotopic tools (C, Sr, U–Th), to identify hydrothermal influences in river water. For
example, Li concentrations show a positive correlation with temperature of hot and cold springs and also a relationship with
δ13C; from this, we can show that several sources of hydrothermal activity influence the rivers of the Lesser Antilles and that
some rivers also reveal an important organic influence. As much as 20% of the subsurface hydrothermal springs go to feed the
rivers. The increasing temperatures result in more dissolved elements being mobilized and an increase in chemical weathering
rates. In addition, using the (230Th/238U) isochron for the well and river dissolved loads in Martinique, Guadeloupe and Réunion, we can evaluate residence times
in the river water, i.e. the average residence time in the water along the circulation path to the sampling point. Alteration
takes longer when the water circulates through thick soil, for example, 400–5,000 years when circulating under an ash profile
and 1,200–15,000 years when circulating through a collapse zone. It would appear that waters circulation is globally three
times longer for subsurface water than for surficial water. The weathering regime in tropical volcanic environments seems
to be controlled mainly by such subsurface circulation with high chemical concentration from hydrothermal inputs. The origin
of these compositions is varied and not controlled by a single hydrothermal spring. Consequently, it is subsurface circulation
that determines the weathering regime in tropical volcanic islands with the main controlling parameters being temperature
and residence time. 相似文献
166.
Cores raised during IODP Expedition 303 off southern Greenland (Eirik Ridge site 1305) and off the Labrador Coast (Orphan Knoll site 1302/1303) were analyzed to establish an isotope stratigraphy, respectively for the “inner” and “outer” basins of the Labrador Sea (LS). These isotopic data also provide information on the Atlantic Meridional Overturning Circulation (AMOC), notably with regard to the intensity of the Western Boundary Under Current (WBUC), which is tightly controlled by the production of Denmark Strait Overflow Water (DSOW), and the production of Labrador Sea Water (LSW) in the inner basin through winter cooling and convection. The upper 184 m of sediment at Eirik Ridge spans marine isotope stages (MIS) 32 to 1. At this site, two distinct regimes are observed: prior to MIS 20, the isotopic record resembles that of the open North Atlantic records of the interval, whereas a more site-specific pattern is observed afterwards. This later pattern was characterized by i) high DSOW production rates and strong WBUC during interglacial stages, as indicated by sedimentation rates, ii) large amplitude δ18O-shifts from glacial stages to interglacial stages (> 2.5‰) and iii) an overall range of δ18O-values significantly more positive than before. At Orphan Knoll, the 105 m record spans approximately 800 ka and provides direct information on linkages between the northeastern sector of the Laurentide Ice Sheet and the North Atlantic. At this site, a shift towards larger amplitude glacial/interglacial ranges of δ18O-values occurred after MIS 13, although isotopic records bear a typical North Atlantic signature, particularly during MIS 5, in contradiction to those of Eirik Ridge, where substages 5a to 5c are barely recognized. Closer examination of δ18O-records in planktic and benthic foraminifera demonstrates the presence of distinct deep-water masses in the inner vs. outer LS basins during MIS 11 and more particularly MIS 5e. Data confirm that the modern AMOC, with LSW formation, seems mostly exclusive to the present interglacial, and also suggest some specificity of each interglacial with respect to the production rate of DSOW and the AMOC, in general. 相似文献
167.
Zintl化合物是以Edward Zintl命名的化合物,是一类由电正性的碱金属或碱土金属与电负性的13族或14族元素形成的特殊金属间化合物。其价键模式可以是离子键、金属键和共价键共存,其中的准金属可以共价键的形式形成各种形式的离子簇,因而其结构复杂多样。这类化合物的部分阴离子簇不仅具有稳定的笼状、层状和链状结构,并且具有特殊的光、电、磁等性能,使得在半导体、催化、电极材料等方面都有应用的前景和发展潜力。介绍了几个特殊Zintl化合物体系,盐湖丰产元素在Zintl化合物中的作用,指出了含有盐湖丰产元素的Zintl化合物的应用前景和方向。 相似文献
168.
Monte Carlo simulations can either be viewed as a numerical method for solving evolutionary equations or as a way for statistically modelling the outcome of chaotic dynamical systems. Thus they are well suited for treating many aspects of cometary dynamics. We present a critical review of past applications of Monte Carlo simulations for both long- and short-period comets indicating the strength and weaknesses of the methods with suggestions for future applications. 相似文献
169.
Dr. Claude Genest 《GeoJournal》1987,15(1):63-66
In 1981, residents of Trois-Rivières-Ouest (Québec) who lived near the Kruger pulp and paper mill began to complain that strong
vibrations were damaging their homes. A study sponsored by the local university led to the identification of three destinct
sectors with regard to the vibrations. These were found to be due to a combination of factors including automobile, rail and
maritime traffic, with the most significant source of vibrations being the Kruger plant itself. Using the data collected in
the study, residents presented a convincing case to both city hall and the Kruger company, and were thus able to obtain a
satisfactory solution to their problems. 相似文献
170.
Marc Fouchard Elena Lega Christiane Froeschlé Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):205-222
It is already known (Froeschlé et al., 1997a) that the fast Lyapunov indicator (hereafter FLI), i.e. the computation on a relatively short time of a quantity related to the largest Lyapunov indicator, allows us to discriminate between ordered and weak chaotic motion. Using the FLI many results have been obtained on the standard map taken as a model problem. On this model we are not only able to discriminate between a short time weak chaotic motion and an ordered one, but also among regular motion between non resonant and resonant orbits. Moreover, periodic orbits are characterised by constant FLI values which appear to be related to the order of periodic orbits (Lega and Froeschlé, 2001). In the present paper we extend all these results to the case of continuous dynamical systems (the Hénon and Heiles system and the restricted three-body problem). Especially for the periodic orbits we need to introduce a new value: the orthogonal FLI in order to fully recover the results obtained for mappings. 相似文献