全文获取类型
收费全文 | 2654篇 |
免费 | 76篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 95篇 |
大气科学 | 167篇 |
地球物理 | 1070篇 |
地质学 | 781篇 |
海洋学 | 154篇 |
天文学 | 331篇 |
综合类 | 14篇 |
自然地理 | 141篇 |
出版年
2021年 | 29篇 |
2020年 | 54篇 |
2019年 | 36篇 |
2018年 | 71篇 |
2017年 | 64篇 |
2016年 | 92篇 |
2015年 | 76篇 |
2014年 | 82篇 |
2013年 | 127篇 |
2012年 | 108篇 |
2011年 | 128篇 |
2010年 | 112篇 |
2009年 | 130篇 |
2008年 | 105篇 |
2007年 | 78篇 |
2006年 | 77篇 |
2005年 | 51篇 |
2004年 | 50篇 |
2003年 | 56篇 |
2002年 | 37篇 |
2001年 | 54篇 |
2000年 | 39篇 |
1999年 | 39篇 |
1998年 | 35篇 |
1997年 | 35篇 |
1996年 | 36篇 |
1995年 | 33篇 |
1994年 | 28篇 |
1993年 | 27篇 |
1992年 | 25篇 |
1990年 | 25篇 |
1989年 | 29篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 30篇 |
1985年 | 42篇 |
1984年 | 34篇 |
1983年 | 40篇 |
1982年 | 38篇 |
1981年 | 36篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 27篇 |
1977年 | 34篇 |
1976年 | 30篇 |
1975年 | 36篇 |
1973年 | 22篇 |
1972年 | 26篇 |
1971年 | 32篇 |
1969年 | 23篇 |
排序方式: 共有2753条查询结果,搜索用时 31 毫秒
71.
Ductile deformation of garnet in mylonitic gneisses from the Münchberg Massif (Germany) 总被引:1,自引:0,他引:1
Axel Vollbrecht Jan Pawlowski Bernd Leiss Till Heinrichs Madlen Seidel Andreas Kronz 《Tectonophysics》2006,427(1-4):153
Mylonitic gneisses from the Münchberg Massif contain single grains (type I) and polycrystalline aggregates (type II) of garnet displaying a distinct elongation parallel to a macroscopic lineation which is interpreted as the result of ductile deformation. Lattice-preferred orientations of quartz (textures) symmetrical to the macroscopic foliation and lineation and the lack of rotational microfabrics indicate that the bulk deformation was pure shear at least during the latest strain increments. Garnet textures measured by EBSD together with microprobe analyses demonstrate that these two structural types of garnet can be related to two different processes of ductile deformation: (1) For the single grains stretching can be attributed to diffusion creep along grain boundary zones (Coble creep). The related mass transfer is indicated by the fact that primary growth zones are cut off at the long faces of the grains while the related strain shadow domains do not show comparable chemical zoning. Pressure solution and precipitation suitable to produce similar structures can be largely ruled out because retrogressive reactions pointing to the presence of free hydrous fluids are missing. (2) For the polycrystalline garnet aggregates consisting of cores grading into fine-grained mantles, dislocation creep and associated rotation recrystallization can be assumed. Continuous lattice rotation from the core to the outer polycrystalline rim allow a determination of the related dominant slip systems which are {100}<010> and equivalent systems according to the cubic lattice symmetry. The same holds for garnets which appear to be completely recrystallized. For this type of fine-grained aggregates an alternative nucleation model is discussed. Due to penetrative dislocation glide in connection with short range diffusion and the resulting lattice rotation, primary growth zones are strongly disturbed.Since for the considered rock unit of the Münchberg Massif peak metamorphic temperatures between 630 and 670 °C can be assumed, this study clearly demonstrates that the inferred processes of ductile garnet deformation can occur not only in HT regimes as often suggested in the literature even if embedded within a matrix of “low-strength” minerals like quartz, feldspars and micas. 相似文献
72.
Jadwiga Wyszkowska Edyta Boros-Lajszner Waldemar Lajszner Jan Kucharski 《Environmental Earth Sciences》2017,76(11):403
Study was carried out to compare the effect of the degree of contamination of soil with copper on the soil enzyme activity, depending on the type of chemical compound with which a metal reaches the soil and on the method of soil use. An effect of increasing doses of copper on growth and the development of spring barley has been studied. The study was carried out as a pot experiment on two types of soil: loamy sand and light loam. Copper was introduced to soil as copper(II) sulphate(VI) and copper(II) chloride at four doses: 150, 300, 450 and 600 mg Cu2+ kg?1 d.m. of soil. Soil without copper was used as a control sample. The experiment showed that contamination of soil with copper applied as CuCl2 and CuSO4·5H2O upset the homeostasis of soil. Dehydrogenases and urease were the most sensitive to contamination of soil with Cu2+, both as copper(II) chloride and as copper(II) sulphate(VI), and acid phosphatase and alkaline phosphatase were the least sensitive. Greater changes in enzymatic activity were observed in loamy sand than in light loam. The differences in the impact of copper(II) sulphate(VI) and copper(II) chloride on the soil microbiome were relatively small, because mean ED50 for copper(II) chloride was 341 mg Cu2+ kg?1 d.m. of soil, and for copper(II) sulphate(VI) it was 364 mg Cu2+ kg?1 d.m. of soil. This inhibitory effect of copper persisted throughout the period of the experiment. The sensitivity of spring barley to copper compounds was lower than the enzymes under study. 相似文献
73.
The distribution of platinum group elements (PGEs) in massive sulfides and hematite–magnetite±pyrite assemblages from the
recently discovered basalt-hosted Turtle Pits hydrothermal field and in massive sulfides from the ultramafic-hosted Logatchev
vent field both on the Mid-Atlantic Ridge was studied and compared to that from selected ancient volcanic-hosted massive sulfide
(VHMS) deposits. Cu-rich samples from black smoker chimneys of both vent fields are enriched in Pd and Rh (Pd up to 227 ppb
and Rh up to 149 ppb) when compared to hematite–magnetite-rich samples from Turtle Pits (Pd up to 10 ppb, Rh up to 1.9 ppb).
A significant positive correlation was established between Cu and Rh in sulfide samples from Turtle Pits. PGE chondrite-normalized
patterns (with a positive Rh anomaly and Pd and Au enrichment), Pd/Pt and Pd/Au ratios close to global MORB, and high values
of Pd/Ir and Pt/Ir ratios indicate mafic source rock and seawater involvement in the hydrothermal system at Turtle Pits. Similarly
shaped PGE chondrite-normalized patterns and high values of Pd/Pt and Pd/Ir ratios in Cu-rich sulfides at Logatchev likely
reflect a similar mechanism of PGE enrichment but with involvement of ultramafic source rocks. 相似文献
74.
Gary M. McMurtry David R. Tappin Peter N. Sedwick Ian Wilkinson Jan Fietzke Bruce Sellwood 《Sedimentary Geology》2007,200(3-4):155-165
Deposits of coral-bearing, marine shell conglomerate exposed at elevations higher than 20 m above present-day mean sea level (MSL) in Bermuda and the Bahamas have previously been interpreted as relict intertidal deposits formed during marine isotope stage (MIS) 11, ca. 360–420 ka before present. On the strength of this evidence, a sea level highstand more than 20 m higher than present-day MSL was inferred for the MIS 11 interglacial, despite a lack of clear supporting evidence in the oxygen-isotope records of deep-sea sediment cores. We have critically re-examined the elevated marine deposits in Bermuda, and find their geological setting, sedimentary relations, and microfaunal assemblages to be inconsistent with intertidal deposition over an extended period. Rather, these deposits, which comprise a poorly sorted mixture of reef, lagoon and shoreline sediments, appear to have been carried tens of meters inside karst caves, presumably by large waves, at some time earlier than ca. 310–360 ka before present (MIS 9–11). We hypothesize that these deposits are the result of a large tsunami during the mid-Pleistocene, in which Bermuda was impacted by a wave set that carried sediments from the surrounding reef platform and nearshore waters over the eolianite atoll. Likely causes for such a megatsunami are the flank collapse of an Atlantic island volcano, such as the roughly synchronous Julan or Orotava submarine landslides in the Canary Islands, or a giant submarine landslide on the Atlantic continental margin. 相似文献
75.
Vladimir Yu. Semenov Josef Pek Antal Ádám Waldemar Jóźwiak Boris Ladanyvskyy Igor M. Logvinov Pavel Pushkarev Jan Vozar 《Acta Geophysica》2008,56(4):957-981
In the years 2001–2003, we accomplished the experimental phase of the project CEMES by collecting long-period magnetotelluric
data at positions of eleven permanent geomagnetic observatories situated within few hundreds kilometers along the south-west
margin of the East European Craton. Five teams were engaged in estimating independently the magnetotelluric responses by using
different data processing procedures. The conductance distributions at the depths of the upper mantle have been derived individually
beneath each observatory. By averaging the individual cross-sections, we have designed the final model of the geoelectrical
structure of the upper mantle beneath the CEMES region. The results indicate systematic trends in the deep electrical structure
of the two European tectonic plates and give evidence that the electrical structure of the upper mantle differs between the
East European Craton and the Phanerozoic plate of west Europe, with a separating transition zone that generally coincides
with the Trans-European Suture Zone. 相似文献
76.
Reconstruction of paleocoastlines for the northwestern South China Sea since the Last Glacial Maximum 总被引:1,自引:0,他引:1
The range of relative sea level rise in the northwestern South China Sea since the Last Glacial Maximum was over 100 m. As
a result, lowland regions including the Northeast Vietnam coast, Beibu Gulf, and South China coast experienced an evolution
from land to sea. Based on the principle of reconstructing paleogeography and using recent digital elevation model, relative
sea level curves, and sediment accumulation data, this paper presents a series of paleogeographic scenarios back to 20 cal.
ka BP for the northwestern South China Sea. The scenarios demonstrate the entire process of coastline changes for the area
of interest. During the late glacial period from 20 to 15 cal. ka BP, coastline slowly retreated, causing a land loss of only
1×104 km2, and thus the land-sea distribution remained nearly unchanged. Later in 15–10 cal. ka BP coastline rapidly retreated and
area of land loss was up to 24×104km2, causing lowlands around Northeast Vietnam and South China soon to be underwater. Coastline retreat continued quite rapidly
during the early Holocene. From 10 to 6 cal. ka BP land area had decreased by 9×104km2, and during that process the Qiongzhou Strait completely opened up. Since the mid Holocene, main controls on coastline change
are from vertical crustal movements and sedimentation. Transgression was surpassed by regression, resulting in a land accretion
of about 10×104km2.
Supported by Key Laboratory of Marginal Sea Geology, Chinese Academy of Sciences (Grant No. MSGL0711), the Guangdong Natural
Science Foundation (Grant No. 04001309) and Open Fund of the Key Laboratory of Marine Geology and Environment, Chinese Academy
of Sciences (Grant No. MGE2007KG04) 相似文献
77.
Summary A general analytical model for travel times of seismic waves propagating in a radially asymmetric Earth, is suggested. It is represented by a series of irreducible spherical tensor products with bipolar spherical coefficients. The main term of the series describes the travel times in a radially symmetric Earth, the others represent corrections due to the spherical assymmetry. The method of least squares is suggested for determining the bipolar spherical coefficients from observed seismic travel times. Since the proposed theory assumes that the analytical representation is related to the reference earth, the corrections to the non-zero focal depth and non-zero sea-level height of the seismographic station must be introduced.
aamuam a aaumua ¶rt; ¶rt;¶rt;aa uu a¶rt;ua ¶rt;¶rt; . mm¶rt;a aam u¶rt; ¶rt;a n¶rt;u m unu uuu uumau. ¶rt;a nuam¶rt;a a¶rt;ua ¶rt;¶rt; . ¶rt;u m aam nna a m a¶rt;ua ¶rt;¶rt;mu. ¶rt;aam un uu uum ¶rt; a¶rt;a¶rt;aa a¶rt;um m¶rt; auu a¶rt;am. ¶rt;aaa mu u¶rt;um u n¶rt;nu -unu¶rt;a u. nuam n ¶rt;u nna n¶rt;mau¶rt;aa, a uu aa u m nm a¶rt;u.相似文献
78.
Summary The morphology of the Wadati-Benioff zone in the region of Southern Kuriles and Hokkaido, based on the distribution of 4015 earthquake foci, verified the existence of an intermediate depth aseismic gap and its relation to active andesitic volcanism. A paleosubduction zone activated by an intermediate depth collision with the active subduction zone was found and described.
u Wadati-Benioff amu uu - u a¶rt;, aa a an¶rt;uu 4015 a mu, nm¶rt;ua mau n¶rt; au u amu a¶rt;um au. a a¶rt;a u nuaa a na¶rt;uu, amuuuaa nmu mu amu ¶rt;uu.相似文献
79.
Summary The atmospheric mean energetic level and corresponding flow pattern are studied theoretically in terms of the prescribed divergence of the horizontal wind vector. The divergence field may reflect the diabatic effect due to particles of extraterrestrial origin. 相似文献
80.
ABSTRACT In many places, magnitudes and frequencies of floods are expected to increase due to climate change. To understand these changes better, trend analyses of historical data are helpful. However, traditional trend analyses do not address issues related to shifts in the relative contributions of rainfall versus snowmelt floods, or in the frequency of a particular flood type. We present a novel approach for quantifying such trends in time series of floods using a fuzzy decision tree for event classification and applied it to maximal annual and seasonal floods in 27 alpine catchments for the period 1980–2014. Trends in flood types were studied with Sen’s slope and double mass curves. Our results reveal a decreasing number of rain-on-snow and an increasing number of short rainfall events in all catchments, with flash floods increasing in smaller catchments. Overall, the results demonstrate the value of incorporating a fuzzy flood-type classification into flood trend analyses. 相似文献