全文获取类型
收费全文 | 2275篇 |
免费 | 126篇 |
国内免费 | 35篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 218篇 |
地球物理 | 556篇 |
地质学 | 1132篇 |
海洋学 | 150篇 |
天文学 | 253篇 |
综合类 | 12篇 |
自然地理 | 83篇 |
出版年
2023年 | 7篇 |
2022年 | 28篇 |
2021年 | 41篇 |
2020年 | 42篇 |
2019年 | 41篇 |
2018年 | 116篇 |
2017年 | 135篇 |
2016年 | 138篇 |
2015年 | 96篇 |
2014年 | 145篇 |
2013年 | 204篇 |
2012年 | 108篇 |
2011年 | 141篇 |
2010年 | 113篇 |
2009年 | 141篇 |
2008年 | 115篇 |
2007年 | 80篇 |
2006年 | 64篇 |
2005年 | 42篇 |
2004年 | 55篇 |
2003年 | 54篇 |
2002年 | 53篇 |
2001年 | 33篇 |
2000年 | 36篇 |
1999年 | 17篇 |
1998年 | 31篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 18篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 17篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 20篇 |
1988年 | 7篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1971年 | 5篇 |
排序方式: 共有2436条查询结果,搜索用时 15 毫秒
991.
Istanbul is home to 40% of the industrial facilities in Turkey. Thirty percent of the population working in industry lives
in the city. Past earthquakes have evidenced that the structural reliability of residential and industrial buildings in the
country is questionable. In the Marmara region the earthquake hazard is very high with a 2% annual probability of occurrence
of a magnitude 7+ earthquake on the main Marmara fault. These facts make the management of industrial risks imperative for
the reduction of socioeconomic losses. In this paper we present a first-order assessment of earthquake damage to the industry
in Istanbul and raise issues for better characterization and quantification of industrial losses and management of urban industrial
risks.
This paper borrows from the project report entitled ‘Earthquake Risk Assessment for Industrial Facilities in Istanbul’. The
full report can be found at http://www.koeri.boun.edu.tr/depremmuh.html under the link ‘Research and Applied Projects’. 相似文献
992.
Lake Seyfe is located in a closed basin near K?r?ehir in the central Anatolian region, Turkey. The aim of this study is to evaluate the groundwater quality and effects of lithogenic contamination carried out in the Lake Seyfe basin, which is represented by various lithologies and groundwater types. Seyfe, Horla and Akp?nar springs are recharged through marbles at the western and southwestern of the basin are ultimately and discharged into the K?z?l?rmak Formation and Lake Seyfe. The waters of deep wells drilled into the marbles are of bicarbonate type (type I) in the Ca2+–Mg2+–HCO3 ? and Ca2+–HCO3 ? facies. Özlühüyük spring and waters from most of trenches and shallow wells, which are fed by the K?z?l?rmak Formation, have a mixed (type II) composition in the Ca2+–Mg2+–HCO3 ?–Cl? facies. Groundwater in the alluvium and K?z?l?rmak Formation along Lake Seyfe has a salty (type III) character in the Na+–Cl? facies. The main reasons of formation and change of the groundwater salinity and hydrochemical facies in the Seyfe basin are causing the various (a) lithogenic pollution and heterogeneity of the K?z?l?rmak Formation, (b) salinity of the upper soil zones, and (c) evaporation of the trench and channel waters open to the atmosphere. Considering parameters such as sodium hazard, specific conductivity, bicarbonate and carbonate hazards, waters in the study area are generally suitable for agricultural usage. 相似文献
993.
Erosion and morphology of a debris flow caused by a glacial lake outburst flood,Western Norway 总被引:5,自引:2,他引:3
This article documents a 240,000-m3 debris flow resulting from a glacial lake outburst flood in Fjærland, Western Norway, May 8, 2004. The event started when a glacial lake breached a moraine ridge. The ensuing debris flow was able to erode material along its path, increasing in volume from about 25,000 to 240,000 m3 before depositing about 3 km from its starting point. Field investigations, pre- and post-flow aerial photographs as well as airborne laser scanning (LIDAR) were used to describe and investigate the flow. The most striking and unusual feature of this case study is the very pronounced erosion and bulking. We have made a detailed study of this aspect. Erosion and entrainment is quantified and the final volume of the debris flow is determined. We also present geometrical and sedimentological features of the final deposit. Based on the Fjærland data, we suggest that a self-sustaining mechanism might partly explain the extreme growth of debris flows traversing soft terrain. 相似文献
994.
995.
François Roure 《Swiss Journal of Geoscience》2008,101(1):5-29
Compressional systems are usually characterized by a positive topography above the sea level, which is continuously modified by the conjugate effects of tectonic contraction or post-orogenic collapse, thermo-mechanical processes in the deep lithosphere and asthenosphere, but also by climate and other surface processes influencing erosion rates.Different types of sedimentary basins can develop in close association with orogens, either in the foreland or in the hinterland. Being progressively filled by erosional products of adjacent uplifted domains, these basins provide a continuous sedimentary record of surficial, crustal and lithospheric deformation at and near plate boundaries.Selected integrated basin-scale studies in the Circum-Mediterranean thrust belts and basins, in Pakistan and the Americas, are used here to document the effects of structures inherited from former orogens, rifts and passive margins, active tectonics and mantle dynamics on the development and long term evolution of synorogenic basins. 相似文献
996.
Florian Genier Jean-Luc Epard François Bussy Tomas Magna 《Swiss Journal of Geoscience》2008,101(2):431-452
Detailed field work and zircon analysis have improved the knowledge of the lithostratigraphy at the base of the Siviez-Mischabel nappe in the Mattertal (St-Niklaus-Törbel area). They confirm the existence of an overturned limb and clarify the structure of the St-Niklaus syncline. The following formations can be observed:
- Polymetamorphic gneisses; composed of paragneisses, amphibolites and micaschists (Bielen Unit, pre-Ordovician).
- Fine-grained, greyish quartzite and graywacke with kerogen-rich horizons (Törbel Formation, presumed Carboniferous).
- Green or white micaschists characterized by brown carbonate spots associated with white conglomeratic quartzites (Moosalp Formation, Early Permian).
- Massive, green or white, fine grained, microconglomeratic or conglomeratic quartzites with characteristic pink quartz pebbles (Bruneggjoch Formation, Late Permian-Early Triassic).
997.
On February 6, 1994, a large debris flow developed because of intense rains in a 800-m-high mountain range called Serra do Cubatão, the local name for the Serra do Mar, located along the coast of the state of São Paulo, Brazil. It affected the Presidente Bernardes Refinery, owned by Petrobrás, in Cubatão. The damages amounted to about US $40 million because of the muck cleaning, repairs, and 3-week interruption of the operations. This prompted Petrobrás to conduct studies, carried out by the authors, to develop protection works, which were done at a cost of approximately US $12 million. The paper describes the studies conducted on debris flow mechanics. A new criteria to define rainfall intensities that trigger debris flows is presented, as well as a correlation of slipped area with soil porosity and rain intensity. Also presented are (a) an actual grain size distribution of a deposited material, determined by laboratory and a large-scale field test, and (b) the size distribution of large boulders along the river bed. Based on theory, empirical experience and back-analysis of the events, the main parameters as the front velocity, the peak discharge and the volume of the transported sediments were determined in a rational basis for the design of the protection works. Finally, the paper describes the set of the protection works built, emphasizing their concept and function. They also included some low-cost innovative works. 相似文献
998.
Production optimization and quality assessment of biodiesel from waste vegetable oil 总被引:6,自引:6,他引:0
A. A. Refaat N. K. Attia H. A. Sibak S. T. El Sheltawy G. I. ElDiwani 《International Journal of Environmental Science and Technology》2008,5(1):75-82
Biodiesel production is worthy of continued study and optimization of production procedures because of its environmentally beneficial attributes and its renewable nature. In Egypt, millions L. of oil used for frying foods are discarded each year into sewage systems. Thus, it adds to the cost of treating effluent or pollutes waterways. This study is intended to consider aspects related to the feasibility of the production of biodiesel from waste/recycled oils in an attempt to help reduce the cost of biodiesel and reduce waste and pollution coming from waste oils. The variables affecting the yield and characteristics of the biodiesel produced from used frying oil were studied, the achieved results were analyzed and a set of recommendations was proposed. From the obtained results, the best yield percentage was obtained using a methanol/oil molar ratio of 6:1, potassium hydroxide as catalyst (1%) and 65 °C temperature for one hour. The yield percentage obtained from waste vegetable oil was comparable to that obtained from neat vegetable oil which reached 96.15% under optimum conditions. From the results it was clear that the produced biodiesel fuel, whether from neat vegetable oil or waste vegetable oil, was within the recommended standards of biodiesel fuel. 相似文献
999.
Cross-Wavelet Analysis: a Tool for Detection of Relationships between Paleoclimate Proxy Records 总被引:1,自引:0,他引:1
Cross-wavelet transform (XWT) is proposed as a data analysis technique for geological time-series. XWT permits the detection
of cross-magnitude, phase differences (= lag time), nonstationarity, and coherency between signals from different paleoclimate
records that may exhibit large stratigraphic uncertainties and noise levels. The approach presented herein utilizes a continuous
XWT technique with Morlet wavelet as the mother function, allows for variable scaling factors for time and scale sampling,
and the automatic extraction of the most significant periodic signals. XWT and cross-spectral analysis is applied on computer
generated time-series as well as two independently sampled proxy records (CO2 content approximated from plant cuticles and paleotemperature derived from δ
18O from marine fossil carbonate) of the last 290 Ma. The influence of nonstationarities in the paleoclimate records that are
introduced by stratigraphic uncertainties were a particular focus of this study. The XWT outputs of the computer-models indicate
that a potential causal relationship can be distorted if different geological time-scale and/or large stratigraphic uncertainties
have been used. XWT detect strong cross-amplitudes (∼200 ppm ‰) between the CO2 and δ
18O record in the 20–50 Myr waveband, however, fluctuating phase differences prevent a statistical conclusion on causal relationship
at this waveband. 相似文献
1000.