全文获取类型
收费全文 | 568篇 |
免费 | 31篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 129篇 |
地球物理 | 118篇 |
地质学 | 213篇 |
海洋学 | 14篇 |
天文学 | 99篇 |
综合类 | 3篇 |
自然地理 | 14篇 |
出版年
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 26篇 |
2013年 | 31篇 |
2012年 | 23篇 |
2011年 | 35篇 |
2010年 | 47篇 |
2009年 | 25篇 |
2008年 | 18篇 |
2007年 | 20篇 |
2006年 | 16篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 20篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 8篇 |
1999年 | 18篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 14篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 12篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有604条查询结果,搜索用时 380 毫秒
31.
Geochemical evidence of an extraterrestrial component in impact melt breccia from the Paleoproterozoic Dhala impact structure,India 下载免费PDF全文
Jayanta Kumar Pati Wen Jun Qu Christian Koeberl Wolf Uwe Reimold Munmun Chakarvorty Ralf Thomas Schmitt 《Meteoritics & planetary science》2017,52(4):722-736
The Paleoproterozoic Dhala structure with an estimated diameter of ~11 km is a confirmed complex impact structure located in the central Indian state of Madhya Pradesh in predominantly granitic basement (2.65 Ga), in the northwestern part of the Archean Bundelkhand craton. The target lithology is granitic in composition but includes a variety of meta‐supracrustal rock types. The impactites and target rocks are overlain by ~1.7 Ga sediments of the Dhala Group and the Vindhyan Supergroup. The area was cored in more than 70 locations and the subsurface lithology shows pseudotachylitic breccia, impact melt breccia, suevite, lithic breccias, and postimpact sediments. Despite extensive erosion, the Dhala structure is well preserved and displays nearly all the diagnostic microscopic shock metamorphic features. This study is aimed at identifying the presence of an impactor component in impact melt rock by analyzing the siderophile element concentrations and rhenium‐osmium isotopic compositions of four samples of impactites (three melt breccias and one lithic breccia) and two samples of target rock (a biotite granite and a mafic intrusive rock). The impact melt breccias are of granitic composition. In some samples, the siderophile elements and HREE enrichment observed are comparable to the target rock abundances. The Cr versus Ir concentrations indicate the probable admixture of approximately 0.3 wt.% of an extraterrestrial component to the impact melt breccia. The Re and Os abundances and the 187Os/188Os ratio of 0.133 of one melt breccia specimen confirm the presence of an extraterrestrial component, although the impactor type characterization still remains inconclusive. 相似文献
32.
Ocean Dynamics - Nachdem mehrere europäische Länder, insbesondere Dänemark und die Niederlande, Offshore-Windparks mit mehreren 100 MW planen, sind auch in Deutschland Initiativen... 相似文献
33.
Matthias Lankhorst David Fratantoni Michel Ollitrault Philip Richardson Uwe Send Walter Zenk 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1615-1632
A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600–1050 dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200–2050 dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e.g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5 Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7 Sv across 16°N between the Antilles islands and the Mid-Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADW east of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow. 相似文献
34.
H. Oelkrug T. Brückel D. Hohlwein A. Hoser W. Prandl 《Physics and Chemistry of Minerals》1988,16(3):246-249
K2Mn2(SO4)3 orders magnetically at TN= 1.75 K. One of the orthorhombic cell edges of the low temperature Langbeinite structure becomes doubled in the magnetically ordered state. The antiferromagnetic spin structure found is characterized by weak or vanishing molecular fields due to nearest neighbours. There are no indications of magnetic order down to 1.45 K in the isomorphic compound K2Co2 (SO4)3. 相似文献
35.
36.
Burghard Brümmer 《Boundary-Layer Meteorology》1991,57(3):295-308
Vertical wind shear at a temperature inversion can be caused by baroclinicity associated with a tilt of the inversion. Four observational cases of tilted inversions are presented. The tilts on horizontal scales of 20–100 km range from 2–10 × 10-3 and the vertical wind shear is between 1 and 25 m/s per 100 m. In general, there is remarkable agreement between observed and geostrophic wind shear.The observations show that the inversion tilt is particularly strong at the edges of mesoscale cloud fields. The Richardson number can reach subcritical values. Cloud fields may be surrounded by a cyclonically rotating wind field and cloud gaps by an anticyclonically rotating wind field. 相似文献
37.
Y.-H. Sung C. L. Ciobanu A. Pring J. Brügger W. Skinner N. J. Cook M. Nugus 《Mineralogy and Petrology》2007,90(3-4):249-270
Summary The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic
belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglüshan
Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8
± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These
data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower
Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts
developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated
study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic
framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime
of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and
lithospheric thinning in East China. 相似文献
38.
Andreas Macrander Rolf H. Käse Uwe Send Héðinn Valdimarsson Steingrímur Jónsson 《Ocean Dynamics》2007,57(2):75-89
In spite of the fundamental role the Atlantic Meridional Overturning Circulation (AMOC) plays for global climate stability,
no direct current measurement of the Denmark Strait Overflow, which is the densest part of the AMOC, has been available until
recently that resolve the cross-stream structure at the sill for long periods. Since 1999, an array of bottom-mounted acoustic
instruments measuring current velocity and bottom-to-surface acoustic travel times was deployed at the sill. Here, the optimization
of the array configuration based on a numerical overflow model is discussed. The simulation proves that more than 80% of the
dense water transport variability is captured by two to three acoustic current profilers (ADCPs). The results are compared
with time series from ADCPs and Inverted Echo Sounders deployed from 1999 to 2003, confirming that the dense overflow plume
can be reliably measured by bottom-mounted instruments and that the overflow is largely geostrophically balanced at the sill. 相似文献
39.
Y. Shao M. Sogalla M. Kerschgens W. Brücher 《Meteorology and Atmospheric Physics》2001,78(3-4):157-181
Summary
In this paper, we examine the effects of land-surface heterogeneity on the calculation of surface-energy and momentum fluxes
in a meso-scale atmospheric model. A series of numerical experiments has been carried out with a combination of different
resolutions for the atmosphere and the land surface, which allows an examination of the aggregation and dynamic effects associated
with land-surface heterogeneity. The numerical results show that for a given atmospheric model resolution, increased land-surface
resolution leads to better estimates of surface-energy and momentum fluxes, and for a given land-surface resolution, increased
atmospheric model resolution also improves the estimates of these fluxes. This latter result contradicts the prevailing view
that subgrid variation in atmospheric data plays only a minor role in estimating the fluxes. It is also shown that subgrid
land-surface heterogeneity leads to increased turbulent fluctuations. The responsible mechanisms of this effect are both the
subgrid variation of surface-energy fluxes and their impact upon the development of convective cells. It is suggested that
subgrid atmospheric motions induced by surface heterogeneity may be an important factor which needs to be considered in subgrid
closure schemes for atmospheric models.
Received August 28, 2000/Revised June 1, 2001 相似文献
40.
Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments 总被引:8,自引:7,他引:8
This paper presents a large palaeolimnological study of the pre-industrial and industrial history of atmospheric lead pollution deposition in Sweden. Both lead concentrations and 206Pb/207Pb ratios have been analysed in 31 lakes covering most of Sweden, plus one lake in north-west Russia. Four of the lakes have varved (annually-laminated) sediments. Isotope analysis is a sensitive and effective method to distinguish pollution lead from natural catchment lead and to detect early pollution influence, because the 206Pb/207Pb ratio in unpolluted background sediments in Sweden was > 1.3, while that of lead from pollution, derived from ores and coal, was < 1.2. The sediments show a consistent picture of past temporal changes in atmospheric lead pollution. These changes include: the first traces of pollution 3,500-3,000 yrs ago; a pollution peak in Greek-Roman Times (about 0 AD); lower lead fall-out between 400 and 900 AD; a significant and permanent increase in atmospheric lead fall-out from about 1000 AD; an increase with the Industrial revolution; a major increase following World War II; the maximum peak in the 1970s; and decreasing fall-out over the last decades. The four varved sediments provide high-resolution records of atmospheric pollution. They reveal pollution peaks about 1200 and 1530 AD which match the history of metal production in Europe. According to the varve records the lead pollution level in the late 1990s had decreased beneath the level of the 1530s. The pollution level 1200 AD was about 35% of the 1980s, when lead pollution was still near its all time high. About 50% of the total accumulated atmospheric lead pollution deposition through time was deposited in the pre-industrial period. The sediments also show a consistent picture of the geographic distribution of atmospheric lead deposition over time, with higher deposition in south Sweden and declining levels to the north, which supports the hypothesis that the main sources of pre-industrial atmospheric lead pollution in Sweden were cultural areas in mainland Europe and Great Britain. 相似文献