全文获取类型
收费全文 | 1021篇 |
免费 | 30篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 55篇 |
大气科学 | 154篇 |
地球物理 | 200篇 |
地质学 | 416篇 |
海洋学 | 61篇 |
天文学 | 137篇 |
综合类 | 1篇 |
自然地理 | 32篇 |
出版年
2021年 | 12篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 34篇 |
2015年 | 21篇 |
2014年 | 37篇 |
2013年 | 49篇 |
2012年 | 35篇 |
2011年 | 38篇 |
2010年 | 40篇 |
2009年 | 43篇 |
2008年 | 31篇 |
2007年 | 46篇 |
2006年 | 28篇 |
2005年 | 30篇 |
2004年 | 20篇 |
2003年 | 25篇 |
2002年 | 34篇 |
2001年 | 23篇 |
2000年 | 13篇 |
1999年 | 20篇 |
1998年 | 9篇 |
1997年 | 20篇 |
1996年 | 11篇 |
1995年 | 24篇 |
1994年 | 13篇 |
1993年 | 10篇 |
1991年 | 21篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 15篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1972年 | 7篇 |
1971年 | 7篇 |
1965年 | 7篇 |
1960年 | 9篇 |
1955年 | 8篇 |
1952年 | 11篇 |
1951年 | 8篇 |
排序方式: 共有1056条查询结果,搜索用时 765 毫秒
291.
The derivation of P and S velocities at the core-mantle boundary (CMB) from long-period diffracted waves by the use of the simple ray-theoretical formulav
CMB=r
c
/p (v
CMB=velocity at the CMB;r
c
=core radius;p=ray parameter) yields apparent velocity values which differ from the true velocities. Using a dominant period of about 20 sec for calculating theoretical seismograms, we found a linear relation between the apparent velocity and the average velocity in a transition zone at the base of the mantle with fixed velocity on top.The ray parameters determined from long-period earthquake data are found to be 4.540±0.035 and 8.427±0.072 sec/deg for Pdiff and Sdiff, respectively. These values yield apparent velocities of 13.378±0.103 for P and 7.207±0.062 km/sec for S waves. By means of the theoretical relation between apparent and average velocity and under the assumption of linear variation of velocity with depth, one can invert the apparent velocities into true CMB velocities of 13.736±0.170 and 7.320±0.124 km/sec. These results imply positive velocity gradients at the base of the mantle and hence no significant departures from adiabaticity and homogeneity.Contribution No. 211 of the Geophysical Institute, University of Karlsruhe. 相似文献
292.
293.
294.
295.
Prof. Dr. R. Hoeppener Dr. G. Schäfer Dr. H. -U. Schwarz Dipl. Phys. H. Mischke 《International Journal of Earth Sciences》1978,67(3):858-879
Quantitative experimental and theoretical investigations, except basic research, should focus only to such parameters which can be measured in the field. This is shown by three examples.
- A model of a discontinuum composed of particles, between which friction occurs during shear is presented. Even at simple shear external and internal stresses are in equilibrium; no rigid body rotation occurs. The theory is examinated experimentally.
- In deformation experiments with clay and sand a development of anisotropy is observed, which can cause shear fractures. The orientation of the normal stress directions can be discovered from the shear sets, their angular distribution, and the rotation of the individual blocks.
- Most folds can be traced back to the following three types, a) Similar folds, b) concentric folds, and c) box folds. b) and c) occur only near the surface and near shear planes, as shown by experiments and field observations. In all other cases the more energy-consuming similar folds are formed. Kink bands are presumably transitional between folds and shear fractures.
296.
Dr. Gerhard H. Eisbacher Dr. H. Gabrielse 《International Journal of Earth Sciences》1975,64(1):85-100
The authors present a tentative model for the relationship between deformation, uplift and molasse sedimentation in the Columbian Orogen of the Canadian Cordillera. Data are mainly drawn from the north-central part of the Columbian Orogen. Two distinct deformational episodes are recognized. The first, probably of mid-Jurassic age, was accompanied by regional metamorphism and resulted in southwesterly directed folds and related faults. This episode of crustal shortening appears to have been the precursor of uplift in the western Columbian Orogen (Omineca Crystalline Belt), causing the progradation of a primogenic non-marine molasse over marine shale and flysch. The second deformation, of probable late Cretaceous to Eocene age, caused overprinting of earlier structures by steep faults in the west and led to the growth of the fold-and-thrust belt of the Rocky Mountains. This episode created a morphogenic drainage system with molasse deposition in intramontane fault basins and along both flanks of the Columbian Orogen. Modal analyses from fluviatile sandstones within the primogenic and morphogenic molasse illustrate the progressive stripping of sedimentary and volcanic units along both sides of the orogenic core zone. Post-orogenic drainage from Miocene to Recent was strongly modified by the development of high-gradient drainage towards the Pacific Ocean. 相似文献
297.
The nature of the near-liquidus phases for a mantle-derived olivine melilitite composition have been determined at high pressure under dry conditions and with various water contents. Olivine and clinopyroxene occur on or near the liquidus and there are no conditions where orthopyroxene crystallizes in equilibrium with the olivine melilitite. We have determined the effect on the liquidus temperature and liquidus phases of substituting CO2 for H2O on a mole for mole basis at 30 kb, using olivine melilitite + 20 wt% H2O at
= 0 and
= (CO2)/(H2+CO2) (mole fraction) = 0.25, 0.5, 0.75 and 1.0 (i.e. olivine melilitite + 38 wt% CO2). Experiments were buffered by the MH or NNO buffers. At 30 kb, CO2 is only slightly less soluble than water for
<0.5 as judged by the slight increase in liquidus temperature on mole-for-mole substitution of CO2 for H2O and at 30 kb, 1200° C,
=
= 0.5 the olivine melilitite contains 8.8 wt% H2O and 21 wt% CO2 in solution. For
1 the CO2 saturated liquidus is depressed 70 ° C below the anhydrous liquidus and the magma dissolves approx. 17% CO2 at 30kb, 1400 ° C,
1,
0. Infrared spectra of quenched glasses have absorption bands characteristic of CO
3
=
and OH- molecules and no evidence for HCO
3
-
. The effect of CO
3
=
molecules dissolved in the olivine melilitite at high pressure is to suppress the near-liquidus crystallization of olivine and clinopyroxene and bring orthopyroxene and garnet on to the liquidus. We infer that olivine melilitite magmas may be derived by equilibrium partial melting (<5%) of pyrolite at 30 kb, 1150–1200 ° C, provided that both H2O and CO2 are present in the source region in minor amounts. Preferred conditions are 0<
<0.5, 0.5<
<1, and at low oxygen fugacities (相似文献
298.
Dr. Helmuth Schöner 《Contributions to Mineralogy and Petrology》1960,7(2):76-103
Comparative investigations were made on the non-carbonate components of calcareous sediments of the upper chalk formation of the Hanover region.The mineral composition of the residues insoluble in 0.5 n HC1 has first been determined optically and by X-ray photographs and described. The quantitative analysis of the components contained was effected by microscopic counting using the phase contrast method up to the grain size of 2 u, and for the clay fractions proper by X-ray phase analyses.In addition to the minor components (feldspars, biotite, pyrite, marcasite, glauconite, heavy minerals and mikro-fossils) the residues contain quartz, muscovite, illite, montmorillonite and kaolinite.The calcareous sediments of the upper senon formation are specially characterized by the occurrence of authigenic heulandite crystals which could be analysed and described here for the first time. Moreover secondary crystallization of quartz, turmaline and albite could be observed in all the samples analysed. 相似文献
299.
Gerhard von Horstig 《International Journal of Earth Sciences》1960,49(2):375-389
Zusammenfassung In der Umgebung von Hof wird unterschieden eine ältere Pressungstektonik in der sudetischen Phase der variskischen Orogenese und eine jüngere Zerrungstektonik. Die Pressungstektonik ist dem NW-Rahmen der Münchberger Gneismasse ähnlich, jedoch von geringerer Intensität. In einer 1. Phase kommt es zu einer Schicht- und Schieferungsfaltung, in einer unmittelbar anschließenden 2. Phase besonders an den Grenzen größerer Schichtkomplexe zu Überschiebungen mit NW- bis N-Vergenz. Die Überschiebungen reißen öfter an NW streichenden Blattverschiebungen auseinander, wodurch das Gefüge im Uhrzeigersinn verdreht wird. Durch die jüngere Zerrungstektonik wurden viele dieser Blattverschiebungen in SW fallende Abschiebungen umgewandelt. Der Wartturmberg wird als autochthone Aufpressung aus der Tiefe gedeutet. 相似文献
300.
Dr. Gerhard Frenzel 《Contributions to Mineralogy and Petrology》1954,4(4):343-376
Ohne ZusammenfassungMeinem hochverehrten Lehrer, Herrn Professor Dr.Paul Ramdohr, zum 65. Geburtstag gewidmet. 相似文献