首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   166篇
  免费   1篇
测绘学   9篇
大气科学   8篇
地球物理   77篇
地质学   53篇
天文学   17篇
自然地理   3篇
  2018年   5篇
  2017年   3篇
  2016年   7篇
  2015年   2篇
  2014年   4篇
  2013年   7篇
  2011年   6篇
  2010年   4篇
  2009年   8篇
  2008年   3篇
  2007年   2篇
  2005年   2篇
  2004年   5篇
  2001年   2篇
  1997年   3篇
  1996年   3篇
  1995年   3篇
  1993年   2篇
  1992年   3篇
  1991年   2篇
  1990年   2篇
  1989年   2篇
  1988年   4篇
  1987年   2篇
  1986年   5篇
  1985年   2篇
  1984年   5篇
  1983年   6篇
  1982年   3篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1977年   4篇
  1976年   4篇
  1975年   2篇
  1973年   6篇
  1972年   2篇
  1971年   3篇
  1970年   2篇
  1969年   2篇
  1968年   2篇
  1967年   2篇
  1966年   2篇
  1964年   3篇
  1963年   1篇
  1961年   3篇
  1960年   3篇
  1959年   1篇
  1957年   1篇
  1949年   1篇
排序方式: 共有167条查询结果,搜索用时 250 毫秒
101.
The main aim of this paper was to investigate the removal efficiency of antimony (Sb) and arsenic (As) from circum-neutral mine drainage in the former Sb mine in Popro? (Slovakia) using a simple field treatment system based on the adsorption onto iron fillings. The treatment system consisted of two batch reactors with a volume of 1 m3: the first was used for settling of spontaneously precipitated ochreous sediments and the second, filled with reactive iron material, was designed to remove Sb and As from mine water. This passively operated treatment system contained 150 kg of low-cost iron fillings and was able to treat approximately 360 l of mine drainage per hour. The average removal efficiency of Sb and As reached 84 and 89% during a period of 2.3 years of the system operation, respectively. On average, dissolved Sb and As concentrations in mine drainage decreased from 175 to 24.3 µg/l and from 452 to 50.6 µg/l, respectively. Based on the electron microprobe (EMP) analyses of corrosion products developed on the surfaces of iron fillings, average Sb and As contents were 0.28 and 0.73 wt%, respectively. The chemical analyses of precipitated HFOs in the settling reactor showed that these ochreous precipitates contained up to 19.3 g/kg Sb and 65.8 g/kg As, indicating their natural role in the removal of the two metalloids from circum-neutral mine drainage. The results of transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses confirmed the presence of ferrihydrite and goethite in ochreous sediments.  相似文献   
102.
Celestial Mechanics and Dynamical Astronomy - Differences among the Earth gravity field models, which were (in Klokočník and Pospíšilová, 1981) expressed as dispersions of...  相似文献   
103.
Quantification of relations between measured variables of interest by statistical measures of dependence is a common step in analysis of climate data. The choice of dependence measure is key for the results of the subsequent analysis and interpretation. The use of linear Pearson’s correlation coefficient is widespread and convenient. On the other side, as the climate is widely acknowledged to be a nonlinear system, nonlinear dependence quantification methods, such as those based on information-theoretical concepts, are increasingly used for this purpose. In this paper we outline an approach that enables well informed choice of dependence measure for a given type of data, improving the subsequent interpretation of the results. The presented multi-step approach includes statistical testing, quantification of the specific non-linear contribution to the interaction information, localization of areas with strongest nonlinear contribution and assessment of the role of specific temporal patterns, including signal nonstationarities. In detail we study the consequences of the choice of a general nonlinear dependence measure, namely mutual information, focusing on its relevance and potential alterations in the discovered dependence structure. We document the method by applying it to monthly mean temperature data from the NCEP/NCAR reanalysis dataset as well as the ERA dataset. We have been able to identify main sources of observed non-linearity in inter-node couplings. Detailed analysis suggested an important role of several sources of nonstationarity within the climate data. The quantitative role of genuine nonlinear coupling at monthly scale has proven to be almost negligible, providing quantitative support for the use of linear methods for monthly temperature data.  相似文献   
104.
This paper presents a unified approach to the least squares spherical harmonic analysis of the acceleration vector and Eötvös tensor (gravitational gradients) in an arbitrary orientation. The Jacobian matrices are based on Hotine’s equations that hold in the Earth-fixed Cartesian frame and do not need any derivatives of the associated Legendre functions. The implementation was confirmed through closed-loop tests in which the simulated input is inverted in the least square sense using the rotated Hotine’s equations. The precision achieved is at the level of rounding error with RMS about $10^{-12}{-}10^{-14}$  m in terms of the height anomaly. The second validation of the linear model is done with help from the standard ellipsoidal correction for the gravity disturbance that can be computed with an analytic expression as well as with the rotated equations. Although the analytic expression for this correction is only of a limited accuracy at the submillimeter level, it was used for an independent validation. Finally, the equivalent of the ellipsoidal correction, called the effect of the normal, has been numerically obtained also for other gravitational functionals and some of their combinations. Most of the numerical investigations are provided up to spherical harmonic degree 70, with degree 80 for the computation time comparison using real GRACE data. The relevant Matlab source codes for the design matrices are provided.  相似文献   
105.
106.
The Teplá-Barrandian unit (TBU) of the Bohemian Massif was a part of the Avalonian-Cadomian belt at the northern margin of Gondwana during Neoproterozoic and Early Cambrian times. New detrital zircon ages and geochemical compositions of Late Neoproterozoic siliciclastic sediments confirm a deposition of the volcano-sedimentary successions of the TBU in a back-arc basin. A change in the geotectonic regime from convergence to transtension was completed by the time of the Precambrian-Cambrian boundary. The accumulation of around 2,500 m Lower Cambrian continental siliciclastics in a Basin-and-Range-type setting was accompanied by magmatism, which shows within-plate features in a few cases, but is predominantly derived from anatectic melts displaying the inherited island arc signature of their Cadomian source rocks. The geochemistry of clastic sediments suggests a deposition in a rift or strike-slip-related basin, respectively. A marine transgression during Middle Cambrian times indicates markedly thinned crust after the Cadomian orogeny. Upper Cambrian magmatism is represented by 1,500 m of subaerial andesites and rhyolites demonstrating several geochemical characteristics of an intra-plate setting. Zircons from a rhyolite give a U-Pb-SHRIMP age of 499±4 Ma. The Cambrian sedimentary and magmatic succession of the TBU records the beginning of an important rifting event at the northern margin of Gondwana.
Kerstin DrostEmail:
  相似文献   
107.
Summary The calibrated variance-covariance matrices of the harmonic geopotential coefficients of the recent combined model JGM 2 has been tested and verified by independent crossover altimetry from TOPEX/Poseidon and ERS 1 using the Latitude Lumped Coefficients in the southern oceans area. Although orbits are not yet available for these missions with other recent models for which error matrices have been released, by comparison with JGM 2 results and field differences we also confirm that the error matrices for the satellite model GRIM 4S4p and the combined data model JGM 3 are also generally valid. Projections of these matrices for a variety of inclinations show that many unused orbits of even moderate altitude (≈ 800 km) will still yield trajectory crossover errors at a level of many tens of centimeters even with the latest orbitgeopotential models.  相似文献   
108.
There is a brightening effect of quasar outputs due to the positive curvature of space in the static Universe, if we use the right expression of distance as an arc3r=R , and not the corrected luminosity distance ofr=Rsin.  相似文献   
109.
110.
Three major allochthonous units have been distinguished on the north-eastern border of the Moldanubian Zone, which differ each from other in lithology and structural and metamorphic evolution. Their present day position displays significant metamorphic and structural inversion resulting from progressive nappe stacking during the Variscan orogeny. The uppermost-Gföhl Unit consists of anatectic rocks containing high temperature/high pressure relics, i.e. granulites, eclogites and garnet peridotites. The rocks of the Gföhl Unit were strongly mylonized during uplift and later also extensively migmatized in the kyanite stability field. The Kouiim Nappe is built up by a sequence of fine-grained leucocratic migmatites with preserved relics of a pre-Variscan deformation event. This event was terminated by the intrusion of coarse-grained porphyritic granites, converted into augen orthogneisses by the Variscan orogeny. The lowermost Micaschist Zone was formed from a sequence of metapelites intercalated with diopsidic amphibolites.During uplift from deep crustal zones the Gföhl Unit cut off a thick slice of the basement crustal material represented by the Kourim Nappe. The quartzo-feldspathic material of the Kourim Nappe acted as a major shear interface because of its extreme ductility under the conditions found in the middle crust. This process occurred under amphibolite facies metamorphism. The continuous uplift of the nappe pile induced another crustal segment in the nappe stack, represented by the Micaschist Zone. The whole nappe sequence was then thrust over the Moldanubian Zone. A westward sense of shear is suggested for the whole uplift history. The kinematic pattern was complicated by later strike-slip ductile faults which finished the recent geological configuration.Correspondence to: J. Synek  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号