全文获取类型
收费全文 | 24841篇 |
免费 | 258篇 |
国内免费 | 1043篇 |
专业分类
测绘学 | 1444篇 |
大气科学 | 2089篇 |
地球物理 | 4592篇 |
地质学 | 11812篇 |
海洋学 | 1069篇 |
天文学 | 1634篇 |
综合类 | 2205篇 |
自然地理 | 1297篇 |
出版年
2024年 | 5篇 |
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 33篇 |
2020年 | 19篇 |
2019年 | 40篇 |
2018年 | 4789篇 |
2017年 | 4068篇 |
2016年 | 2604篇 |
2015年 | 269篇 |
2014年 | 124篇 |
2013年 | 56篇 |
2012年 | 1019篇 |
2011年 | 2755篇 |
2010年 | 2045篇 |
2009年 | 2337篇 |
2008年 | 1912篇 |
2007年 | 2375篇 |
2006年 | 66篇 |
2005年 | 203篇 |
2004年 | 413篇 |
2003年 | 425篇 |
2002年 | 272篇 |
2001年 | 68篇 |
2000年 | 62篇 |
1999年 | 20篇 |
1998年 | 24篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1976年 | 7篇 |
1958年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
761.
The paper presents the testing of the possibility of determining the heights of GPS points in the homogeneous field in the
new Croatian Height Reference System (HVRS71) by using the method of height transformation. The testing was made in the area
of Zagreb. As part of the field works, normal orthometric heights of 27 GPS points were determined according to the new height
system, by transferring the benchmark heights using the geometric levelling method, thus obtaining GPS/levelling points of
known ellipsoidal and normal orthometric heights. The GPS/levelling points served as the basis for determining the transformation
models that enabled the computation of normal orthometric heights from ellipsoidal heights of any GPS point in the observed
area. The empirical data used for modelling were reduced undulation dN values of GPS/levelling points. As part of the dN modelling
with parametric functions, the approximation surfaces were obtained on the basis of three polynomials: FN310, FN312 and FN318.
The transformation models were also tested using non-parametric Watson and Loess algorithms. The FN318 and Loess models yielded
the best results. 相似文献
762.
Lee Hannah Marc Steele Emily Fung Pablo Imbach Lorriane Flint Alan Flint 《Climatic change》2017,140(1):63-77
Improved cookstoves have been identified in Mexico as a key opportunity to advance sustainable local development priorities in disadvantaged regions while mitigating climate change. This paper reviews the Patsari Cookstove Project initiated in 2003 by an NGO, Interdisciplinary Group on Appropriate Rural Technology (GIRA). The project applied an interdisciplinary and participative user-centered approach to disseminate improved cookstoves in rural Mexico, with a special focus on indigenous and poor rural communities. To date, GIRA and the Patsari Network have disseminated thousands of stoves using a “training to trainers” model. Benefits from the project include tangible improvements in users’ health, as well as savings in time and money expended on fuelwood procurement and use. The project has also documented substantive environmental benefits from significant mitigation of greenhouse gas (GHG) emissions associated with traditional open fires. To sustain scaling up efforts over the long-term, two networks have been created: The Patsari Network, which includes several organizations promoting Patsari stoves for household users, and the Tsiri Network, which supports local food security and the empowerment of indigenous women through the promotion of institutional cookstoves. Through appropriately designed and implemented local interventions, the project demonstrates that the goals of advancing sustainable local development in rural areas and climate change mitigation may not be contradictory, and may in fact reinforce one another. 相似文献
763.
Mauro Cacace Ulf Bayer Anna Maria Marotta 《International Journal of Earth Sciences》2008,97(5):899-913
The large-scale crustal deformations observed in the Central European Basin System (CEBS) are the result of the interplay
between several controlling factors, among which lateral rheological heterogeneities play a key role. We present a finite-element
integral thin sheet model of stress and strain distribution within the CEBS. Unlike many previous models, this study is based
on thermo-mechanical data to quantify the impact of lateral contrasts on the tectonic deformation. Elasto-plastic material
behaviour is used for both the mantle and the crust, and the effects of the sedimentary fill are also investigated. The consistency
of model results is ensured through comparisons with observed data. The results resemble the present-day dynamics and kinematics
when: (1) a weak granite-like lower crust below the Elbe Fault System is modelled in contrast to a stronger lower crust in
the area extending north of the Elbe Line throughout the Baltic region; and (2) a transition domain in the upper mantle is
considered between the shallow mantle of the Variscan domain and the deep mantle beneath the East European Craton (EEC), extending
from the Elbe Line in the south till the Tornquist Zone. The strain localizations observed along these structural contrasts
strongly enhance the dominant role played by large structural domains in stiffening the propagation of tectonic deformation
and in controlling the basin formation and the evolution in the CEBS. 相似文献
764.
Chengbiao Leng Yuhui Wang Xingchun Zhang Jianfeng Gao Wei Zhang Xinying Xu 《中国地球化学学报》2018,37(1):47-59
The Kukaazi Pb–Zn–Cu–W polymetallic deposit, located in the Western Kunlun orogenic belt, is a newly discovered skarn-type deposit. Ore bodies mainly occur in the forms of lenses and veins along beddings of the Mesoproterozoic metamorphic rocks. Three ore blocks, KI, KII, and KIII, have been outlined in different parts of the Kukaazi deposit in terms of mineral assemblages. The KI ore block is mainly composed of chalcopyrite, scheelite, pyrrhotite, sphalerite, galena and minor pyrite, arsenopyrite, and molybdenite, whereas the other two ore blocks are made up of galena, sphalerite, magnetite and minor arsenopyrite and pyrite. In this study, we obtained a molybdenite isochron Re–Os age of 450.5 ± 6.4 Ma (2σ, MSWD = 0.057) and a scheelite Sm–Nd isochron age of 426 ± 59 Ma (2σ, MSWD = 0.49) for the KI ore block. They are broadly comparable to the ages of granitoid in the region. Scheelite grains from the KI ore block contain high abundances of rare earth elements (REE, 42.0–95.7 ppm) and are enriched in light REE compared to heavy REE, with negative Eu anomalies (δEu = 0.13–0.55). They display similar REE patterns and Sm/Nd ratios to those of the coeval granitoids in the region. Moreover, they also have similar Sr and Nd isotopes [87Sr/86Sr = 0.7107–0.7118; εNd(t) = ?4.1 to ?4.0] to those of such granitoids, implying that the tungsten-bearing fluids in the Kukaazi deposit probably originate from the granitic magmas. Our results first defined that the Early Paleozoic granitoids could lead to economic Mo–W–(Cu) mineralization at some favorable districts in the Western Kunlun orogenic belt and could be prospecting exploration targets. 相似文献
765.
Mohamed M. Hamdy Mohamed A. Abd El-Wahed Ismaeel A. Thabet 《Arabian Journal of Geosciences》2017,10(18):414
Dykes predominate within the Neoproterozoic rocks, especially granites, of Wadi El Redi-Wadi Lahami area in the southern Eastern Desert of Egypt. The dyke swarms form three major suites: from the oldest to the youngest, they are basaltic andesite—Suite 1 (E-W and ENE-WSW), rhyolite—Suite 2 (NE-SW), and andesite—Suite 3 (NNE-SSW, NNW-SSE, and NW-SE). Despite the wide ranges of the dyke compositions, the feldspar and amphibole are usually the essential forming minerals. The plagioclase arrays between Ab0.9An99.10 in the basaltic andesite and Ab98.80An0.70 in the rhyolite, while sanidine ranges from Or44.60Ab49.70 to Or98.40Ab1.60. Amphibole in Suite 1 and 3 (Al2O3, TiO2, Na2O, and K2O are the lowest and those of SiO2 and CaO are the highest) samples are usually magnesio-hornblende, whereas it is edenite and tschermakite in Suite 2 dykes. Despite all parent magmas have calc-alkaline affinity, some elements such as Ni show an erratic behavior against the progressing differentiation from one magma chamber and implying for an assimilation of the country rocks. The high contents of amphibole, the depletion in Ti, and the enrichment in large-ion lithophile elements (such as K, Rb, Ba, Sr, and Ba) compared to the primitive mantle composition are consistent with parent hydrous melts generated due to extension above the subduction zone. The estimated compositions of liquids in equilibrium with amphiboles and the pressures at which they crystallized (4.61–7.8 kbar for the Suite 2 and 1.5–2 kbar for the Suites 1 and 3) are greatly varied. These are indications for a difference in the source regions of the parent magmas of the studied dykes. It is supposed that the Suite 1 and 2 dykes are a conjugate set emplaced due to the NW-SE crustal extension in the Arabian-Nubian shield, whereas the Suite 3 dykes generated due to the rifting along the Red Sea. 相似文献
766.
Challenges of using remote sensing and GIS in developing nations 总被引:2,自引:1,他引:2
767.
This paper presents the computation of time series of the 22 July 2007 M 4.9 Kharsali earthquake. It occurred close to the Main Central Thrust (MCT) where seismic gap exists. The main shock and 17 aftershocks were located by closely spaced eleven seismograph stations in a network that involved VSAT based real-time seismic monitoring. The largest aftershock of M 3.5 and other aftershocks occurred within a small volume of 4 × 4 km horizontal extent and between depths of 10 and 14 km. The values of seismic moment (M ∘) determined using P-wave spectra and Brune’s model based on f 2 spectral shape ranges from 1018 to 1023 dyne-cm. The initial aftershocks occurred at greater depth compared to the later aftershocks. The time series of ground motion have been computed for recording sites using geometric ray theory and Green’s function approach. The method for computing time series consists in integrating the far-field contributions of Green’s function for a number of distributed point source. The generated waveforms have been compared with the observed ones. It has been inferred that the Kharsali earthquake occurred due to a northerly dipping low angle thrust fault at a depth of 14 km taking strike N279°E, dip 14° and rake 117°. There are two regions on the fault surface which have larger slip amplitudes (asperities) and the rupture which has been considered as circular in nature initiated from the asperity at a greater depth shifting gradually upwards. The two asperities cover only 10% of the total area of the causative fault plane. However, detailed seismic imaging of these two asperities can be corroborated with structural heterogeneities associated with causative fault to understand how seismogenesis is influenced by strong or weak structural barriers in the region. 相似文献
768.
Sushant S Naik Meloth Thamban A Rajakumar Witty D’Souza C M Laluraj Arun Chaturvedi 《Journal of Earth System Science》2010,119(1):41-49
Ice and firn core studies provide one of the most valuable tools for understanding the past climate change. In order to evaluate the temporal isotopic variability recorded in ice and its relevance to environmental changes, stable isotopes of oxygen and hydrogen were studied in a firn core from coastal Dronning Maud Land, East Antarctica. The annual δ 18O profile of the core shows a close relation to the El Niño Southern Oscillation (ENSO) variability. The ENSO indices show significant correlation with the surface air temperatures and δ 18O values of this region during the austral summer season and support an additional influence related to the Southern Annular Mode (SAM). The correlation between the combined ENSO-SAM index and the summer δ 18O record seems to have been caused through an atmospheric mechanism. Snow accumulation in this region illustrates a decreasing trend with opposite relationships with δ 18O data and surface air temperature prior and subsequent to the year 1997. A reorganization of the local water cycle is further indicated by the deuterium excess data showing a shift around 1997, consistent with a change in evaporation conditions. The present study thus illustrates the utility of ice-core studies in the reconstruction of past climate change and suggests possible influence of climatic teleconnections on the snow accumulation rates and isotopic profiles of snow in the coastal regions of east Antarctica. 相似文献
769.
Nabeel H. Al-Saigh 《Journal of the Geological Society of India》2010,76(4):399-402
In 1986 shortly after the impounding of Mosul reservoir, shallow earthquakes began occurring in the immediate reservoir vicinity, with magnitudes up to ML 3.0, at rates of up to 3 events per week. These events were almost certainly reservoir-induced and coincided with steadily increasing water levels. Cluster of epicenters was observed in the area located within a complex fault zone called the Sinjar-Dohouk-Kuchuk fault system. The presence of such fault system considers a potential source of earthquakes. A composite fault plane solution, based on first p-wave motion analyses, indicates that the mechanisms of seismicity were right-lateral strike-slip faulting along N44°E plane dipping 58° NW, in conformity with the local tectonics. 相似文献
770.
A series of fully three-dimensional(3 D) numerical simulations of flow past a free-to-oscillate curved flexible riser in shear flow were conducted at Reynolds number of 185–1015. The numerical results obtained by the two-way fluid–structure interaction(FSI) simulations are in good agreement with the experimental results reported in the earlier study. It is further found that the frequency transition is out of phase not only in the inline(IL) and crossflow(CF) directions but also along the span direction. The mode competition leads to the non-zero nodes of the rootmean-square(RMS) amplitude and the relatively chaotic trajectories. The fluid–structure interaction is to some extent reflected by the transverse velocity of the ambient fluid, which reaches the maximum value when the riser reaches the equilibrium position. Moreover, the local maximum transverse velocities occur at the peak CF amplitudes, and the values are relatively large when the vibration is in the resonance regions. The 3 D vortex columns are shed nearly parallel to the axis of the curved flexible riser. As the local Reynolds number increases from 0 at the bottom of the riser to the maximum value at the top, the wake undergoes a transition from a two-dimensional structure to a 3 D one. More irregular small-scale vortices appeared at the wake region of the riser, undergoing large amplitude responses. 相似文献