全文获取类型
收费全文 | 1088篇 |
免费 | 36篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 131篇 |
地球物理 | 224篇 |
地质学 | 482篇 |
海洋学 | 37篇 |
天文学 | 220篇 |
综合类 | 4篇 |
自然地理 | 36篇 |
出版年
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 28篇 |
2015年 | 31篇 |
2014年 | 36篇 |
2013年 | 49篇 |
2012年 | 46篇 |
2011年 | 50篇 |
2010年 | 40篇 |
2009年 | 45篇 |
2008年 | 54篇 |
2007年 | 35篇 |
2006年 | 37篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 28篇 |
2002年 | 31篇 |
2001年 | 25篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 24篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 16篇 |
1977年 | 8篇 |
1976年 | 15篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1972年 | 6篇 |
1970年 | 5篇 |
排序方式: 共有1145条查询结果,搜索用时 15 毫秒
71.
Understanding the degree of sea/saltwater intrusion in coastal regions is of great significance to treating the intrusion and improving the environment. Based on the character analysis of the sea/saltwater intrusion, five factors were selected in the fuzzy-synthetical evaluation approach to form the index system, so as to evaluate the degree of sea/saltwater intrusion in southern Laizhou Bay. The results show that the sea/saltwater intrusion is stronger in the middle and northern areas and weaker on the sides and in southern area; currently, the intrusion is relatively serious, and the intrusion area has covered about 68.2% of the areas under study, among which the heavily intruded area is over 50%. Based on the factors analysis of the occurrence and development of sea/saltwater intrusion, the thesis proposes treatment measures. 相似文献
72.
In (semi-)arid regions, available water resources are scarce and groundwater resources are often overused. Therefore, the option to increase available water resources by managed aquifer recharge (MAR) via infiltration of captured surface runoff was investigated for two basins in northern Jordan. This study evaluated the general suitability of catchments to generate sufficient runoff and tried to identify promising sites to harvest and infiltrate the runoff into the aquifer for later recovery. Large sets of available data were used to create regional thematic maps, which were then combined to constraint maps using Boolean logic and to create suitability maps using weighted linear combination. This approach might serve as a blueprint which could be adapted and applied to similar regions. The evaluation showed that non-committed source water availability is the most restricting factor for successful water harvesting in regions with <200 mm/a rainfall. Experiences with existing structures showed that sediment loads of runoff are high. Therefore, the effectiveness of any existing MAR scheme will decrease rapidly to the point where it results in an overall negative impact due to increased evaporation if maintenance is not undertaken. It is recommended to improve system operation and maintenance, as well as monitoring, in order to achieve a better and constant effectiveness of the infiltration activities. 相似文献
73.
In the Bavarian Alps (Germany), west of the Isar River, the abyssal deposits of the Lower Barremian to Upper Campanian Rhenodanubian Group consist of siliciclastic and calcareous turbidites alternating with hemipelagic non-calcareous mudstones. The up to 1500-m-thick succession, deposited in the Penninic Basin to the south of the European Plate, is characterized by a low mean sedimentation rate (c. 25 mm kyr−1) over 60 million years. Palaeocurrents and turbidite facies distribution patterns suggest that sedimentation occurred on a weakly inclined abyssal plain. The highest sedimentation rates (up to 240 mm kyr−1) were associated with the calcareous mud turbidites of the newly defined Röthenbach Subgroup, which includes the Piesenkopf, Kalkgraben and Hällritz formations (Middle Coniacian to Middle Campanian). These calcareous turbidites prograded from the west, and interfinger towards the east with red hemipelagic claystone. A high sea level presumably favoured pelagic carbonate production and accumulation on the shelves and on internal platforms in the western part of the basin, whereas siliciclastic shelves with steep slope angles have bordered the eastern part of the basin, where a dearth of turbidite sedimentation and increased Cretaceous oceanic red beds deposition occurred. In contrast to the eustatically-induced Middle Coniacian to Lower Campanian Cretaceous oceanic red beds (calcareous nannoplankton zones CC14 to CC18), red hemipelagites of Early Cenomanian age (upper part of calcareous nannoplankton zone CC9) and early Late Campanian age (upper part of zone CC21 and zone CC22) are interpreted as the result of regional tectonic activity. 相似文献
74.
Axel Müller Bernd Leiss Klaus Ullemeyer Karel Breiter 《International Journal of Earth Sciences》2011,100(7):1515-1532
The lattice-preferred orientation (LPOs) of two late-Variscan granitoids, the Meissen monzonite and the Podlesí dyke granite,
were determined from high-resolution time-of-flight neutron diffraction patterns gained at the diffractometer SKAT in Dubna,
Russia. The results demonstrate that the method is suitable for the LPO analysis of polyphase, relatively coarse-grained (0.1–6 mm)
rocks. The Meissen monzonite has a prominent shape-preferred orientation (SPO) of the non-equidimensional minerals feldspar,
mica and amphibole, whereas SPO of the Podlesí granite is unapparent at the hand-specimen scale. The neutron diffraction data
revealed distinct LPOs in both granitoids. The LPO of the non-equidimensional minerals feldspar, mica and amphibole developed
mainly during magmatic flow. In the case of the Meissen monzonite, the magmatic flow was superimposed by regional shear tectonics,
which, however, had no significant effect on the LPOs. In both samples, quartz shows a weak but distinct LPO, which is atypical
for plastic deformation and different in the syn-kinematic Meissen monzonite and the post-kinematic Podlesí granite. We suggest
that, first of all, the quartz LPO of the Meissen monzonite is the result of oriented growth in an anisotropic stress field.
The quartz LPO of the Podlesí granite, which more or less resembles a deformational LPO in the flattening field of the local
strain field, developed during magmatic flow, whereby the rhombohedral faces of the quartz crystals adhered to the (010) faces
of aligned albite and to the (001) faces of zinnwaldite. Due to shape anisotropy of their attachments, the quartz crystals
were passively aligned by magmatic flow. Thus, magmatic flow and oriented crystal growth are the major LPO-forming processes
in both granitoids. For the Meissen monzonite, the solid-state flow was too weak to cause significant crystallographic re-orientation
of the minerals aligned by magmatic flow. Finally, the significance of our results for the evaluation of the regional tectonic
environment during magma emplacement is discussed. The discussion on the regional implications of the more methodologically
oriented results provides the basis for future, more regionally aimed studies in view of the fabric characteristics of such
plutons and their developing mechanisms. 相似文献
75.
In the night from 8/9 April 2009, shortly after midnight on Maundy Thursday before Easter, several people in Gross Flottbek,
Hamburg, felt unusual strong ground shocks so that some of them left their houses in fear of earthquake shaking. Police and
fire brigade received phone calls of worried residents. A few days later, Internet pages were published where people reported
their observations. On 21 April 2009 at about 8 p.m. local time, a second ground-shaking event was felt. Damage to buildings
or infrastructure did not occur to our knowledge. The Institute of Geophysics, University of Hamburg, installed from 22 April
to 17 May 2009 three temporal seismic stations in the epicentral area. Seismological data from two nearby stations at the
Deutsches Elektronen-Synchrotron at 1 km and the Geophysical Institute at 7 km distance were collected and integrated to the
temporal network. The events occurred above the roof of the shallow Othmarschen Langenfelde salt diapir, in an area known
for active sinkhole formation and previous historic ground-shaking events. The analysis of the seismological data shows that
three shallow micro-earthquakes occurred from 8 to 21 April at a depth of about 100 m, the largest one with a moment magnitude
of about M
W 0.6. Depth location of such shallow events is difficult with standard methods and is here constrained by waveform modeling
of surface waves. Earthquakes occurring in soft sediments within the uppermost 100 m are a rare phenomena and cannot be explained
by standard models. Rupture process in soft sediments differs from those on faults in more competent rock. We discuss the
rupture and source mechanism of the events in the context of previous historic shocks and existing sinkhole and deformation
data. Although the event was weak, the rupture duration of 0.3 s was unusual long. Three possible models for the generation
of repeated ground-shaking events in Gross Flottbek are developed and discussed, implying quit different hazards for subsidence,
ground motion, and sinkhole formation. Our favored model postulates that roof failure occurs in an existing soil cavity beneath
the epicenter at a depth of about 100 m. Other models bearing a smaller geo-hazard cannot be disproved with the data available,
but future geophysical experiments may be planned to resolve this question. 相似文献
76.
77.
Tamás Mikes Dominik Christ Rüdiger Petri István Dunkl Dirk Frei Mária Báldi-Beke Joachim Reitner Klaus Wemmer Hazim Hrvatović Hilmar von Eynatten 《Swiss Journal of Geoscience》2008,101(1):31-54
Sandwiched between the Adriatic Carbonate Platform and the Dinaride Ophiolite Zone, the Bosnian Flysch forms a c. 3000 m thick, intensely folded stack of Upper Jurassic to Cretaceous mixed carbonate and siliciclastic sediments in the Dinarides. New petrographic, heavy mineral, zircon U/Pb and fission-track data as well as biostratigraphic evidence allow us to reconstruct the palaeogeology of the source areas of the Bosnian Flysch basin in late Mesozoic times. Middle Jurassic intraoceanic subduction of the Neotethys was shortly followed by exhumation of the overriding oceanic plate. Trench sedimentation was controlled by a dual sediment supply from the sub-ophiolitic high-grade metamorphic soles and from the distal continental margin of the Adriatic plate. Following obduction onto Adria, from the Jurassic–Cretaceous transition onwards a vast clastic wedge (Vranduk Formation) was developed in front of the leading edge, fed by continental basement units of Adria that experienced Early Cretaceous synsedimentary cooling, by the overlying ophiolitic thrust sheets and by redeposited elements of coeval Urgonian facies reefs grown on the thrust wedge complex. Following mid-Cretaceous deformation and thermal overprint of the Vranduk Formation, the depozone migrated further towards SW and received increasing amounts of redeposited carbonate detritus released from the Adriatic Carbonate Platform margin (Ugar Formation). Subordinate siliciclastic source components indicate changing source rocks on the upper plate, with ophiolites becoming subordinate. The zone of the continental basement previously affected by the Late Jurassic–Early Cretaceous thermal imprint has been removed; instead, the basement mostly supplied detritus with a wide range of pre-Jurassic cooling ages. However, a c. 80 Ma, largely synsedimentary cooling event is also recorded by the Ugar Formation, that contrasts the predominantly Early Cretaceous cooling of the Adriatic basement and suggests, at least locally, a fast exhumation. 相似文献
78.
79.
Niranjan D. Chatterjee Klaus Miller Walter Olbricht 《Physics and Chemistry of Minerals》1994,21(1-2):50-62
Internally consistent thermodynamic data, including their uncertainties and correlations, are reported for 22 phases of the quaternary system CaO-Al2O3-SiO2-H2O. These data have been derived by simultaneous evaluation of the appropriate phase properties (PP) and reaction properties (RP) by the novel technique of Bayes estimation (BE). The thermodynamic model used and the theory of BE was expounded in Part I of this paper. Part II is the follow-up study illustrating an application of BE. The input for BE comprised, among others, the a priori values for standard enthalpy of formation of the i-th phase, Δf H i 0 , and its standard entropy, S i 0 , in addition to the reaction reversal constraints for 33 equilibria involving the relevant phases. A total of 269 RP restrictions have been processed, of which 107 turned out to be non-redundant. The refined values for Δf H i 0 and S i 0 obtained by BE, including their 2σ-uncertainties, appear in Table 4; the Appendix reproduces the corresponding correlation matrix. These data permit generation of computed phase diagrams with 2σ-uncertainty envelopes based on conventional error propagation; Fig. 3 depicts such a phase diagram for the system CaO-Al2O3-SiO2. It shows that the refined dataset is capable of yielding phase diagrams with uncertainty envelopes narrow enough to be geologically useful. The results in Table 4 demonstrate that the uncertainties of the prior values for Δf H i Emphasis>0 , given in Table 1, have decreased by up to an order of magnitude, while those for S i 0 improved by a factor of up to two. For comparison, Table 4 also lists the refined Δf H i 0 and S i 0 data obtained by mathematical programming (MAP), minimizing a quadratic objective function used earlier by Berman (1988). Examples of calculated phase diagrams are given to demonstrate the advantages of BE for deriving internally consistent thermodynamic data. Although P-T curves generated from both MAP and BE databases will pass through the reversal restrictions, BE datasets appear to be better suited for extrapolations beyond the P-T range explored experimentally and for predicting equilibria not constrained by reversals. 相似文献
80.
Klaus Töpfer 《GeoJournal》1994,33(4):349-354
Environmental policy is increasingly becoming an indispensable part of modern policy to maintain peace and security. After the end of the East-West conflict, a new cold war between North and South is looming on the horizon. It is caused by a steadily widening gap between the poverty of the South and the wealth of the North, which has been gained not least at the expense of the environment worldwide, and thus also of the South.There is a need for a parallel development between the disarmament process in the classical sense and a disarmament process in a material sense to promote an economic, social and ecological development which is consistent in itself and coordinated with regard to its effects.Appropriate instruments to achieve this, besides international conventions, include the opening up of markets, ecologically honest prices, technical cooperation and not least the enforcement of environmentally compatible and resource-saving forms of industry and ways of life in the industrialised countries. 相似文献