全文获取类型
收费全文 | 631篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 58篇 |
大气科学 | 90篇 |
地球物理 | 140篇 |
地质学 | 253篇 |
海洋学 | 30篇 |
天文学 | 39篇 |
综合类 | 5篇 |
自然地理 | 34篇 |
出版年
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 10篇 |
2018年 | 17篇 |
2017年 | 25篇 |
2016年 | 27篇 |
2015年 | 22篇 |
2014年 | 20篇 |
2013年 | 35篇 |
2012年 | 29篇 |
2011年 | 34篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 28篇 |
2007年 | 28篇 |
2006年 | 9篇 |
2005年 | 26篇 |
2004年 | 16篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1987年 | 5篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1966年 | 4篇 |
1965年 | 3篇 |
1950年 | 3篇 |
排序方式: 共有649条查询结果,搜索用时 15 毫秒
1.
2.
Joana F.M.F. Cardoso Denis Langlet Jos F. Loff Ana R. Martins Johannes IJ. Witte Paulo T. Santos Henk W. van der Veer 《Journal of Sea Research》2007,57(4):303-315
The Pacific oyster Crassostrea gigas was introduced in Europe for commercial purposes in the mid 1960s. It was initially thought that low winter temperatures would restrain this species' reproduction and settlement; however, its present distribution in areas where no introduction has taken place suggests that natural invasion and expansion has occurred. Along the European coast, wild populations of Pacific oysters are already found from northern Germany to southern Portugal. Whether C. gigas will continue to further expand through northern waters will depend on its physiological performance. In this study, the performance of wild oyster populations has been studied in terms of growth and reproduction at three stations: La Rochelle (France; 46°N), Yerseke (Oosterschelde estuary, The Netherlands, 51°N), and Texel (Wadden Sea estuary, The Netherlands, 53°N). The French population had the lowest somatic-shell mass ratio and an increase in maximum shell length, somatic and gonadal mass was observed from France to the Netherlands. In addition, mean oocyte diameter decreased significantly from south to north. The combination of increasing gonadal mass and decreasing oocyte volume suggests an increasing reproductive output in terms of egg numbers from France to The Netherlands. Differences in temperature between locations will at least be partly responsible for the observed patterns; however, other environmental factors (such as food availability, predation pressure, sediment type and/or seston concentration) cannot be excluded. Since smaller eggs (oocytes) are thought to have a longer development time, the environmental conditions along the Dutch coast may result in increased larval dispersal and possibly in further population expansion. 相似文献
3.
Joana F.M.F. Cardoso Johannes IJ. Witte Henk W. van der Veer 《Journal of Sea Research》2007,57(4):316-324
The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm3. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns. 相似文献
4.
Submarine groundwater discharge (SGD) into a coastal lagoon off Perth, Western Australia, contains nitrate and silicate in concentrations two orders of magnitude higher than those of the receiving waters. This discharge delivers enough nitrate to replace that dissolved in the lagoon water mass about every eight days and enough silicate to replace the lagoon silicate in about 48 days. The delivery rate of nitrate nitrogen by SGD is equal to about 48% of that required for observed growth rates of lagoon macrophytes. Surface salinity is lower close to the shore as a result of SGD. During calm conditions a salinity front was observed in the lagoon, with a nearshore pool of nutrient-enriched water floating above the more saline ocean water. 相似文献
5.
U. Altenberger R. Schmid R. Oberhänsli 《International Journal of Earth Sciences》2008,97(6):1301-1314
As part of the Yangtze plate, segments of the Dabie Shan terrane of Central China underwent ultra-high pressure metamorphism
during Triassic subduction. We studied the geochemistry of the abundant eclogites to evaluate the nature of the protoliths
and their geodynamic setting. Although some previous geochemical work exists, the analyses and interpretation herein are based
on a new subdivision of the ultra-high pressure sequence into basement and cover units (Changpu and Ganghe Unit), revealing
new and important results. In addition, eclogites of the so-called HP Unit south of the UHP units were studied. Whereas the
large ion lithophile elements indicate postmagmatic, metasomatic changes of some samples, the high-field strength elements
and the rare earth elements display original magmatic trends. The geochemical characteristics of the eclogites of the ultra-high
pressure areas display a strong dependence on their “structural” and geographic position. The eclogites of the basement and
the Changpu Unit indicate melt intrusion and extrusion in a continental rift system, i.e. during extensional tectonics. In
contrast, the Ganghe Unit is characterized by a pronounced chemical homogeneity. The composition of the eclogites indicates
generation from a mantle source highly influenced by slab-derived fluids. Those of the HP Unit show similar characteristics.
Magmatism of the Ganghe and HP Unit probably occurred in a continental arc setting. A similar age for both units, geographically
and/or tectonically separated, is possible. The geodynamic interpretation based on the geochemistry of the four units points
to a Neoproterozoic scenario in which the protoliths of the HP and the cover units could have been of similar age and deposited
in one evolving geological system. A rift-related larger-scale basin might have formed, e.g. a continental back-arc basin
behind a magmatic arc after or simultaneous to sedimentation and magmatism in the magmatic arc. Alternatively, magmatism occurred
in independent geodynamic settings, distinct in time and space. The units were juxtaposed during exhumation, after subduction
to varying depths. 相似文献
6.
Marco Herwegh Jean-Pierre Hürzeler O. Adrian Pfiffner Stefan M. Schmid Rainer Abart Andreas Ebert 《Swiss Journal of Geoscience》2008,101(2):323-340
This excursion guide results form a field trip to the Glarus nappe complex organized by the Swiss Tectonic Studies Group in 2006. The aim of the excursion was to discuss old and recent concepts related to the evolution of the Glarus thrust. The major aspects were (i) the interplay between deformation, fluid flow and geochemical alteration, (ii) episodic versus continuous deformation and fluid flow, and (iii) the link between large-scale structures, microstructures, and geochemical aspects. Despite 150 years of research in the Glarus nappe complex and the new results discussed during the excursion, there exist controversies that still are unsolved. 相似文献
7.
Ghislain Trullenque Karsten Kunze Renee Heilbronner Holger Stünitz Stefan M. Schmid 《Tectonophysics》2006,424(1-2):69-97
Microfabrics were analysed in calcite mylonites from the rim of the Pelvoux massif (Western Alps, France). WNW-directed emplacement of the internal Penninic units onto the Dauphinois domain produced intense deformation of an Eocene-age nummulitic limestone under lower anchizone metamorphic conditions (slightly below 300 °C). Two types of microfabrics developed primarily by dislocation creep accompanied by dynamic recrystallisation in the absence of twinning. Coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry. Their texture (crystallographic preferred orientation, CPO) is characterised by two c-axis maxima, symmetrically oriented at 15° from the normal to the macroscopic foliation. Non-coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterised by a single oblique c-axis maximum tilted with the sense of shear by about 15°. From the analysis of suitably oriented slip systems for the main texture components under given kinematics it is inferred that the orthorhombic textures, which developed in coaxial kinematics, favour activity of <10–11> and <02–21> slip along the f and r planes, respectively, with minor contributions of basal-<a> slip. In contrast, the monoclinic textures, which developed during simple shear, are most suited for duplex <a> slip along the basal plane. The transition between the dominating slip systems for the orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallisation upon texture development. Since oblique c-axis maxima documented in the literature are most often rotated not with but against the shear sense, calcite textures alone should not be used as unequivocal shear sense indicators, but need to be complemented by microstructural criteria such as shape preferred orientations, grain size estimates and amount of twinning. 相似文献
8.
Michael Stipp Holger Stünitz Rene Heilbronner Stefan M. Schmid 《Journal of Structural Geology》2002,24(12)
Near the eastern end of the Tonale fault zone, a segment of the Periadriatic fault system in the Italian Alps, the Adamello intrusion produced a syn-kinematic contact aureole. A temperature gradient from 250 to 700 °C was determined across the Tonale fault zone using critical syn-kinematic mineral assemblages from the metasedimentary host rocks surrounding deformed quartz veins. Deformed quartz veins sampled along this temperature gradient display a transition from cataclasites to mylonites (frictional–viscous transition) at 280±30 °C. Within the mylonites, zones characterized by different dynamic recrystallization mechanisms were defined: Bulging recrystallization (BLG) was dominant between 280 and 400 °C, subgrain rotation recrystallization (SGR) in the 400–500 °C interval, and the transition to dominant grain boundary migration recrystallization (GBM) occurred at 500 °C. The microstructures associated with the three recrystallization mechanisms and the transitions between them can be correlated with experimentally derived dislocation creep regimes. Bulk texture X-ray goniometry and computer-automated analysis of preferred [c]-axis orientations of porphyroclasts and recrystallized grains are used to quantify textural differences that correspond to the observed microstructural changes. Within the BLG- and SGR zones, porphyroclasts show predominantly single [c]-axis maxima. At the transition from the SGR- to the GBM zone, the texture of recrystallized grains indicates a change from [c]-axis girdles, diagnostic of multiple slip systems, to a single maximum in Y. Within the GBM zone, above 630±30 °C, the textures also include submaxima, which are indicative of combined basal a- and prism [c] slip. 相似文献
9.
Siberian river run-off and Late Quaternary glaciation in the southern Kara Sea, Arctic Ocean: preliminary results 总被引:3,自引:0,他引:3
Ruediger Stein Frank Niessen Klaus Dittmers Michael Levitan Frank Schoster Johannes Simstich Tatjana Steinke Oleg V. Stepanets 《Polar research》2002,21(2):315-322
The extent of the Barents-Kara Ice Sheet during the eastern Last Glacial Maximum (LGM) is not yet fully known. A detailed echo-sounding survey performed during the Boris Petrov Expedition 2001 permitted the detailed mapping of part of it. Based on the profiling results, a southern connection between the LGM Barents-Kara Ice Sheet and a local ice sheet on Taymyr Peninsula appears to be unlikely. Based on sediment core data and profiling results, most of the terrigenous river-derived material accumulated in the estuaries during late Holocene times, whereas during early Holocene times of lowered sea level major amounts were transported further offshore and accumulated on the shelf. During the post-glacial sea level rise, the main depocentre migrated southward, reaching its present position no earlier than about 6 cal. Ky BP (or 5.2 Kya). Future studies of accelerator mass spectrometry (AMS) 14 C-dated sediment cores will allow a detailed reconstruction of the variability of fluvial sediment discharge and the history of glaciation in the Kara Sea during late Quaternary times. 相似文献
10.
The beginning of dehydration melting in the tonalite system (biotite-plagioclase-quartz) is investigated in the pressure
range of 2–12 kbar. A special method consisting of surrounding a crystal of natural plagioclase (An45) with a biotite-quartz mixture, and observing reactions at the plagioclase margin was employed for precise determination
of the solidus for dehydration melting. The beginning of dehydration melting was worked out at 5 kbar for a range of compositions
of biotite varying from iron-free phlogopite to iron-rich Ann70, with and without titanium, fluorine and extra aluminium in the biotite. The dehydration melting of phlogopite + plagioclase
(An45) + quartz begins between 750 and 770°C at pressures of 2 and 5 kbar, at approximately 740°C at 8 kbar and between 700 and
730°C at 10 kbar. At 12 kbar, the first melts are observed at temperatures as low as 700°C. The data indicate an almost vertical
dehydration melting solidus curve at low pressures which bends backward to lower temperatures at higher pressures (> 5 kbar).
The new phases observed at pressures ≤ 10 kbar are melt + enstatite + clinopyroxene + potassium feldspar ± amphibole. In addition
to these, zoisite was also observed at 12 kbar. With increasing temperature, phlogopite becomes enriched in aluminium and
deficient in potassium. Substitution of octahedral magnesium by aluminium and titanium in the phlogopite, as well as substitution
of hydroxyl by fluorine, have little effect on the beginning of dehydration melting temperatures in this system. The dehydration
melting of biotite (Ann50) + plagioclase (An45) + quartz begins 50°C below that of phlogopite bearing starting composition. Solid reaction products are orthopyroxene +
clinopyroxene + potassium feldspar ± amphibole. Epidote was also observed above 8 kbar, and garnet at 12 kbar (750°C). The
experiments on the iron-bearing system performed at ≤ 5 kbar were buffered with NiNiO. The f
O
2 in high pressure runs lies close to CoCoO. With the substitution of octahedral magnesium and iron by aluminium and titanium,
and replacement of hydroxyl by fluorine in biotite, the beginning of dehydration melting temperatures in this system increase
up to 780°C at 5 kbar, which is 70°C above the beginning of dehydration melting of the assemblage containing biotite (Ann50) of ideal composition. The dehydration melting at 5 kbar in the more iron-rich Ann70-bearing starting composition begins at 730°C, and in the Ann25-bearing assemblage at 710°C. This indicates that quartz-biotite-plagioclase assemblages with intermediate compositions of
biotite (Ann25 and Ann50) melt at lower temperatures as compared to those containing Fe-richer or Mg-richer biotites. This study shows that the dehydration
melting of tonalites may begin at considerably lower temperatures than previously thought, especially at high pressures (>5
kbar).
Received: 27 December 1995 / Accepted: 7 May 1996 相似文献