全文获取类型
收费全文 | 766篇 |
免费 | 17篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 27篇 |
大气科学 | 37篇 |
地球物理 | 156篇 |
地质学 | 321篇 |
海洋学 | 23篇 |
天文学 | 151篇 |
综合类 | 1篇 |
自然地理 | 72篇 |
出版年
2023年 | 5篇 |
2020年 | 5篇 |
2019年 | 16篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 18篇 |
2014年 | 33篇 |
2013年 | 31篇 |
2012年 | 24篇 |
2011年 | 30篇 |
2010年 | 29篇 |
2009年 | 54篇 |
2008年 | 34篇 |
2007年 | 33篇 |
2006年 | 37篇 |
2005年 | 27篇 |
2004年 | 22篇 |
2003年 | 37篇 |
2002年 | 34篇 |
2001年 | 12篇 |
2000年 | 18篇 |
1999年 | 23篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1971年 | 8篇 |
1955年 | 4篇 |
1949年 | 3篇 |
排序方式: 共有788条查询结果,搜索用时 15 毫秒
21.
Thomas Backhaus Rolf Altenburger sa Arrhenius Hans Blanck Michael Faust Antonio Finizio Paola Gramatica Matthias Grote Marion Junghans Wiebke Meyer Manuela Pavan Tobias Porsbring Martin Scholze Roberto Todeschini Marco Vighi Helge Walter L. Horst Grimme 《Continental Shelf Research》2003,23(17-19):1757
Freshwater and marine ecosystems are exposed to various multi-component mixtures of pollutants. Nevertheless, most ecotoxicological research and chemicals regulation focus on hazard and exposure assessment of individual substances only, the problem of chemical mixtures in the environment is ignored to a large extent. In contrast, the assessment of combination effects has a long tradition in pharmacology, where mixtures of chemicals are specifically designed to develop new products, e.g. human and veterinary drugs or agricultural and non-agricultural pesticides. In this area, two concepts are frequently used and are thought to describe fundamental relationships between single substance and mixture effects: Independent Action (Response Addition) and Concentration Addition. The question, to what extent these concepts may also be applied in an ecotoxicological and regulatory context may be considered a research topic of major importance, as the concepts would allow to make use of already existing single substance toxicity data for the predictive assessment of mixture toxicities. Two critical knowledge gaps are identified: (a) There is a lack of environmental realism, as a huge part of our current knowledge about the applicability of the concepts is restricted to artificial situations with respect to mixture composition or biological effect assessment. (b) The knowledge on what exactly is needed for using the concepts as tools for the predictive mixture toxicity assessment is insufficient. Both gaps seriously hamper the necessary, scientifically sound consideration of mixture toxicities in a regulatory context.In this paper, the two concepts will be briefly introduced, the necessity of considering the toxicities of chemical mixtures in the environment will be demonstrated and the applicability of Independent Action and Concentration Addition as tools for the prediction and assessment of mixture toxicities will be discussed. An overview of the specific aims and approaches of the BEAM project to fill in the identified knowledge gaps is given and first results are outlined. 相似文献
22.
From March 1989 until May 1995 overall 675 hauls were performed using a commercial stow net vessel to get information concerning spatial and seasonal distribution, length frequency distribution, stock situation and migration patterns of lampreys in the Elbe estuary in northern Germany.2217 river lampreys (Lampetra fluviatilis) and 10 sea lampreys (Petromyzon marinus) were caught during the whole study period. The river lamprey occurred in 40.3% of the performed stow net hauls. The catch success was highest in the western main channel, whereas the frequency of occurrence of river lampreys was only about 10.9% at the most upstream site in the southern marginal area. In 1989 and 1990 significantly more than 50% of the hauls contained river lampreys. In contrast, from 1991 to 1995 their frequency of occurrence was lower than 40%, in 1991 even lower than 20%. Sea lampreys occurred only at 6 from 9 sampled sites and were only observed in 1990 and 1992-1994.Total lengths of river lampreys varied between 7 and 46 cm. Based on the length frequency distribution, the following three size classes of river lampreys were separated: LF I (7 to 16 cm), LF II (17-26 cm) and LF III (27-46 cm). The majority of the caught individuals could be grouped in size class LF III. Total lengths of sea lampreys ranged between 69 and 85 cm and were restricted to only one size class (PM III).70% of all sea lampreys were caught in April and May. Most of the sea lampreys were observed in the eastern main channel. The maximum average abundance of river lampreys was observed with 6.75 Ind · m−3 · 10−6 in the same area in 1992. However, in 1993 and 1994 the highest average abundances of river lampreys occurred in the western main channel.Based on redundance analysis, a significant correlation between the abundances of lampreys and the environmental variables autumn, spring, summer, salinity, water temperature, grain size, new moon and first moon quarter was found. The downstream migrating river lampreys of size class LF I und the sea lampreys during their anadromous spawning migration showed highest abundances mainly in spring, whereas high abundances of river lampreys of size class LF II in the feeding phase occurred in summer. The presence of both size classes LF I and LF II confirms the successful reproduction of river lampreys in the catchment area of the Elbe. The observation of river lampreys of size class LF III during their anadromous spawning migration was closely correlated with the variable autumn. A spring spawning migration of river lampreys was not observed. 相似文献
23.
We report here refined values of the transformation enthalpy for xanthoconite to proustite (54.81 kJ/mol) and pyrostilpnite
to pyrargyrite (40.32 kJ/mol). Additionally, the enthalpy for the transformation of trechmannite to smithite (5.82 kJ/mol)
has been determined. The refinement was possible by taking into account a previously unknown dependence of electrochemical
signals on the amount of substance undergoing the reduction process.
Received December 21, 1995/Revised, accepted June 29, 1996 相似文献
24.
Georges Aouad Valérie Geoffroy Jean-Marie Meyer Jean-Louis Crovisier Denis Damidot Peter Stille 《Comptes Rendus Geoscience》2005,337(15):1340-1347
The influence of microorganisms on mineral alteration is not easy to determine in environmental conditions, because of the difficulty to raise for comparison purposes an identical but abiotic system. Another problem in this context is the choice of reliable tracers to evaluate the alteration rate of materials during in vitro experiments. To face such difficulties, we elaborated a defined medium allowing both the growth of Pseudomonas aeruginosa and a precise measurement of the elements solubilized from the minerals. Thanks to this medium, we were able to quantitatively determine the amounts of major elements solubilized from the materials in the presence of bacterial growth, compared to a sterile system. Moreover, the analysis by ICP-MS of trace elements was possible after a chromatographic treatment, which selectively eliminated 99% of the sodium content of the medium. To cite this article: G. Aouad et al., C. R. Geoscience 337 (2005). 相似文献
25.
Gold mineralization at Hutti is confined to a series of nine parallel, N–S to NNW–SSE trending, steeply dipping shear zones.
The host rocks are amphibolites and meta-rhyolites metamorphosed at peak conditions of 660±40°C and 4±1 kbar. They are weakly
foliated (S1) and contain barren quartz extension veins. The auriferous shear zones (reefs) are typically characterized by four alteration
assemblages and laminated quartz veins, which, in places, occupy the entire reef width of 2–10 m, and contain the bulk of
gold mineralization. A <1.5 m wide distal chlorite-sericite (+biotite, calcite, plagioclase) alteration zone can be distinguished
from a 3–5 m wide proximal biotite-plagioclase (+quartz, muscovite, calcite) alteration zone. Gold is both spatially and temporally
associated with disseminated arsenopyrite and pyrite mineralization. An inner chlorite-K-feldspar (+quartz, calcite, scheelite,
tourmaline, sphene, epidote, sericite) alteration halo, which rims the laminated quartz veins, is characterized by a pyrrhotite,
chalcopyrite, sphalerite, ilmenite, rutile, and gold paragenesis. The distal chlorite-sericite and proximal biotite-plagioclase
alteration assemblages are developed in microlithons of the S2–S3 crenulation cleavage and are replaced along S3 by the inner chlorite-K-feldspar alteration, indicating a two-stage evolution for gold mineralization. Ductile D2 shearing, alteration, and gold mineralization formed the reefs during retrograde evolution and fluid infiltration under upper
greenschist to lower amphibolite facies conditions (560±60°C, 2±1 kbar). The reefs were reactivated in the D3 dextral strike-slip to oblique-slip environment by fault-valve behavior at lower greenschist facies conditions (ca. 300–350°C),
which formed the auriferous laminated quartz veins. Later D4 crosscutting veins and D5 faults overprint the gold mineralization. The alteration mineralogy and the structural control of the deposit clearly points
to an orogenic style of gold mineralization, which took place either during isobaric cooling or at different levels of the
Archean crust. From overlaps in the tectono-metamorphic history, it is concluded that gold mineralization occurred during
two tectonic events, affecting the eastern Dharwar craton in south India between ca. 2550 – 2530 Ma: (1) The assemblage of
various terranes of the eastern block, and (2) a tectono-magmatic event, which caused late- to posttectonic plutonism and
a thermal perturbation. It differs, however, from the pre-peak metamorphic gold mineralization at Kolar and the single-stage
mineralization at Ramagiri. Notably, greenschist facies gold mineralization occurred at Hutti 35–90 million years later than
in the western Dharwar craton.
Editorial handling: G. Beaudoin 相似文献
26.
Reactive surface area is one of the key parameters for studying the kinetics of mineral dissolution. The common practice in experimental kinetics is to normalize the dissolution rate to the surface area measured by the BET method. The relationship between BET surface area and the reactive surface area is not trivial in minerals such as smectites, which possess both internal and external surface areas, and in which the dissolution is controlled by the chemical attack on the edge surface. The present study examines two proxies for the reactive surface area of the Clay Mineral Society reference smectite SAz-1: BET surface area and the edge surface area measured using AFM.Since smectites are very microporous, their BET surface area is strongly influenced by the degassing procedure. It is demonstrated that outgassing the smectite powder at 135°C in a 15 mL min−1 N2 gas flow for at least 24 hours minimizes contribution from micropores to less than 11% of the BET surface area.Following dissolution experiments in solutions with a low electrolyte concentration, the BET surface area increased from 34 ± 2 m2 g−1 in raw SAz-1 to 127 ± 13 m2 g−1 in SAz-1 sample recovered from dissolution experiments. This increase in BET surface area is explained by a decrease in the average size of the smectite aggregates, and by an increase in microporosity due to the depletion in the major interlayer cation, i.e., Ca2+. As the BET surface area of the raw smectite sample includes considerably less microporosity compared to the BET surface area of the smectite recovered from dissolution experiments, the former is a better approximation of the external surface area of the dried sample powder.AFM measurements show that there is no correlation between the specific external surface area of the sample and its specific edge surface area. This observation is explained by the platy morphology of the smectite particle in which the specific external surface area depends linearly on the height reciprocal, whereas the specific edge surface area is independent of the particles height and depends linearly on the sum of the reciprocals of the length of the axes. Therefore, there is no reason to expect a correlation between the BET and the edge surface area. Our results show that the edge surface area (4.9 ± 0.7 m2 g−1) of the smectite particles cannot be predicted based on its external surface area (136 ± 20 m2 g−1). Therefore, the BET surface area cannot serve as a proxy for the reactive surface area. We suggest using AFM measurements of the specific edge surface area as an alternative proxy for the reactive surface area of smectite. 相似文献
27.
Well-preserved Holocene terraces along the South Fork Payette River in central Idaho provide a record of fluvial system behavior in a steep mountain watershed characterized by weathered and erodible Idaho Batholith granitic rocks. Terrace deposit ages were provided by 14C dating of charcoal fragments and optically stimulated luminescence (OSL) dating of sandy sediments. Along with pairing of many terrace tread heights, these data indicate episodic downcutting during the Holocene, with a mean incision rate of ~0.9 m/ka from ~7 ka to present. Prior to 7 ka, the river incised to within~3 m of current bankfull, but then aggraded by ~5 m over at least a ~10 km-long reach in an episode centered ~7–6 ka. Aggradation may relate to (1) increased hillslope sediment input from landslides and debris flows in steep tributary basins with abundant grussified granitic bedrock, (2) possible local landslide-damming of the channel, (3) decreased peak discharge, or (4) a combination of these factors. Middle Holocene channel aggradation ca. 7–6 ka corresponds with a period of prolonged and widespread aridity in the northern Rocky Mountains. Between ~5 and 1.3 ka, the river aggraded slightly and then remained stable, forming a prominent terrace tread at ~3 m above current bankfull. Modest aggradation to vertical stability of the South Fork Payette River at the 1.5 m terrace level ~1.0–0.7 ka corresponds with large fire-related debris flows in tributaries during Medieval droughts. Three intervals of incision (~5.5–5 ka, 1.3–1.0 ka and 0.5 ka) correspond with frequent but small fire-related sedimentation events and generally cooler, wetter conditions suggesting increased snowmelt runoff discharges. Other possible drivers of channel incision include an increase in stochastic or climate-modulated large storms and floods and a reduction in delivery of hillslope sediment to the channel. Aggradation is more confidently tied to climate through increases in hillslope sediment delivery and (or) decreased stream power, both likely related to warmer, drier conditions (including high-severity fires) that reduce snowmelt and decrease vegetation cover on steep slopes. Thus, the Holocene terraces of the South Fork Payette River do not reflect simple stepwise incision with periods of vertical stability and lateral migration, but record substantial episodes of aggradation as well. We infer that increases in hillslope erosion and mass movements combined with reduced discharges during prolonged droughts episodically reverse the post-glacial trend of downcutting, in particular during the middle Holocene. The present bedrock-dominated channel implies a strong tendency toward incision in the late Holocene. 相似文献
28.
Larisa A. Savelieva Andrei A. Andreev Raphael Gromig Dmitry A. Subetto Grigory B. Fedorov Volker Wennrich Bernd Wagner Martin Melles 《Boreas: An International Journal of Quaternary Research》2019,48(2):349-360
The new pollen record from the upper 12.75 m of a sediment core obtained in Lake Ladoga documents regional vegetation and climate changes in northwestern Russia over the last 13.9 cal. ka. The Lateglacial chronostratigraphy is based on varve chronology, while the Holocene stratigraphy is based on AMS 14C and OSL dates, supported by comparison with regional pollen records. During the Lateglacial (c. 13.9–11.2 cal. ka BP), the Lake Ladoga region experienced several climatic fluctuations as reflected in vegetation changes. Shrub and grass communities dominated between c. 13.9 and 13.2 cal. ka BP. The increase in Picea pollen at c. 13.2 cal. ka BP probably reflects the appearance of spruce in the southern Ladoga region at the beginning of the Allerød interstadial. After c. 12.6 cal. ka BP, the Younger Dryas cooling caused a significant decrease in spruce and increase in Artemisia with other herbs, indicative of tundra‐ and steppe‐like vegetation. A sharp transition from tundra‐steppe habitats to sparse birch forests characterizes the onset of Holocene warming c. 11.2 cal. ka BP. Pine forests dominated in the region from c. 9.0 to 8.1 cal. ka BP. The most favourable climatic conditions for deciduous broad‐leaved taxa existed between c. 8.1 and 5.5 cal. ka BP. Alder experiences an abrupt increase in the local vegetation c. 7.8 cal. ka BP. The decrease in tree pollen taxa (especially Picea) and the increase in herbs (mainly Poaceae) probably reflect human activity during the last 2.2 cal. ka. Pine forests have dominated the region since that time. Secale and other Cerealia pollen as well as ruderal herbs are permanently recorded since c. 0.8 cal. ka BP. 相似文献
29.
Segmentation and kinematics of the North America‐Caribbean plate boundary offshore Hispaniola 下载免费PDF全文
Sylvie Leroy Nadine Ellouz‐Zimmermann Jordane Corbeau Frédérique Rolandone Bernard Mercier de Lépinay Bertrand Meyer Roberte Momplaisir José‐Luis Granja Bruña Anne Battani Céline Baurion Evgueni Burov Valérie Clouard Rémy Deschamps Christian Gorini Youri Hamon Manfred Lafosse Jottin Leonel Laetitia Le Pourhiet Pilar Llanes Estrada Nicolas Loget Francis Lucazeau Daniel Pillot Jeffrey Poort Kevin R. Tankoo José‐Luis Cuevas José‐Fernando Alcaide Claude Jean Poix Alfonso Muñoz‐Martin Serge Mitton Yamil Rodriguez Julien Schmitz Leonardo Seeber Andres Carbo‐Gorosabel Santiago Muñoz 《地学学报》2015,27(6):467-478
We explored the submarine portions of the Enriquillo–Plantain Garden Fault zone (EPGFZ) and the Septentrional–Oriente Fault zone (SOFZ) along the Northern Caribbean plate boundary using high‐resolution multibeam echo‐sounding and shallow seismic reflection. The bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between Haiti and Jamaica (EPGFZ) and 300 km between the Dominican Republic and Cuba (SOFZ). The primary plate‐boundary structures are a series of strike‐slip fault segments associated with pressure ridges, restraining bends, step overs and dogleg offsets indicating very active tectonics. Several distinct segments 50–100 km long cut across pre‐existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike‐slip regime. Along the most recent trace of the SOFZ, we measured a strike‐slip offset of 16.5 km, which indicates steady activity for the past ~1.8 Ma if its current GPS‐derived motion of 9.8 ± 2 mm a?1 has remained stable during the entire Quaternary. 相似文献
30.