全文获取类型
收费全文 | 1697篇 |
免费 | 116篇 |
国内免费 | 84篇 |
专业分类
测绘学 | 90篇 |
大气科学 | 101篇 |
地球物理 | 454篇 |
地质学 | 884篇 |
海洋学 | 81篇 |
天文学 | 131篇 |
综合类 | 29篇 |
自然地理 | 127篇 |
出版年
2024年 | 5篇 |
2023年 | 13篇 |
2022年 | 56篇 |
2021年 | 64篇 |
2020年 | 67篇 |
2019年 | 78篇 |
2018年 | 150篇 |
2017年 | 130篇 |
2016年 | 177篇 |
2015年 | 81篇 |
2014年 | 182篇 |
2013年 | 172篇 |
2012年 | 93篇 |
2011年 | 103篇 |
2010年 | 63篇 |
2009年 | 73篇 |
2008年 | 57篇 |
2007年 | 39篇 |
2006年 | 54篇 |
2005年 | 30篇 |
2004年 | 23篇 |
2003年 | 25篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 13篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1897条查询结果,搜索用时 46 毫秒
71.
In this paper a methodology has been presented for constructing the most critical accelerogram from among a be class of candidate accelerograms for a given site and structure. This most critical accelerogram could be used to assess seismic resistance of a structure with a high level of confidence. Specifically, the method superimposes accelerograms recorded at similar sites to create the candidate accelerograms, then uses optimization and approximation techniques find the most critical accelerogram. The most critical accelerogram is defined as the one which maximizes damage is structure, as computed by non-linear dynamic structural analysis, as well as satisfies constraints on ground parameters to ensure credibility. The damage has been defined as cumulative inelastic energy dissipation or sure of interstorey drifts. The method is applied to ten examples in the paper. 相似文献
72.
Samir el-Gaby Osman el-Nady Ali Khudeir 《International Journal of Earth Sciences》1984,73(3):1019-1036
The Egyptian basement rocks are gathered into three major rock groups, viz. Meatiq Group (oldest), Abu Ziran Group and Hammamat Group (youngest); the last two groups belong to the Pan-African orogenic cycle. The Meatiq Group is an old crystalline basement cropping out in gneiss domes. The Abu Ziran Group comprises the geosynclinal association which is formed of a lower ophiolite unit overlain by metasediments, volcanoclastics and locally intermediate volcanics having clear island arc characters. The Hammamat Group comprises molasse-type clastics, and penecontemporaneous Dokhan Volcanics of andesite to rhyolite composition; syn to late-tectonic calc-alkaline granites are the plutonic equivalents of the Dokhan Volcanics.The studied area lies within the foreland fold and thrust belt of a continental margin orogen. Ophiolites, particularly serpentinites, crop out along the trace of the sole thrust between the Meatiq infrastructure and the imbricated Abu Ziran nappe.Swells, developed along two geanticlines, were centers of marked calc-alkaline magmatic activity associated, at least, with gold mineralization.
Zusammenfassung Die Gesteine des ägyptischen Kristallins sind in drei Hauptgruppen unterteilt: Meatiq Group (älteste), Abu Ziran Group und Hammamat Group (jüngste); die letzten zwei Gruppen gehören dem Pan-Afrikanischen Zyklus an. Die Meatiq-Gruppe stellt einen alten Sokkel dar, der in Gneisdomen auftritt. Die Abu-Ziran-Gruppe umfaßt die Geosynklinal-Assoziation, die aus einer unteren ophiolitischen Einheit besteht, überlagert von Sedimenten, volkanoklastischen Sedimenten und lokalen intermediären Vulkaniten mit ausgeprägten Inselbogen-Eigenschaften. Die Hammamat-Gruppe besteht aus Molassetyp klastischen Sedimenten und zeitlich assoziierte Dokhan Volcanics andesitischer bis rhyolitischer Zusammensetzung. Die synbis spät-tektonische Kalkalkaligranite sind die plutonischen Aequivalente der Dokhan Volcanics.Das untersuchte Gebiet liegt im Vorland-Falten- und Decken-Gürtel eines Kontinentalrand-Orogens. Ophiolite, insbesondere die Serpentinite, treten entlang dem Ausbiß der Überschiebungsfläche zwischen dem Meatiq-Sockelstockwerk und der Abu-Ziran-Decke auf.Schwellen in Form zweier Geantiklinalen waren Zentren aktiver kalkalkaliner magmatischer Tätigkeit, begleitet zumindest von Goldvererzungen.
Résumé Les roches du socle égyptien se répartissent en trois groupes majeurs: Meatiq Group (le plus ancien); Abu Ziran Group et Hammamat Group (le plus récent); les deux derniers groupes appartiennent au cycle orogénique Pan-Africain.Le Meatiq Group est un socle cristallin ancien affleurant en dômes gneissiques. Le Abu Ziran Group comprend une association géosynclinale formée d'une unité ophiolitique inférieure suivie par des métasédiments, des volcanoclastites et localement par des roches volcaniques intermédiaires à caractere d'arc insulaire. Le Hammamat Group comprend des roches clastiques du type molassique, et des roches volcaniques pénécontemporaines de composition andésitique à rhyolitique (Dokhan Volcanics); des granites calco-alcalins syntectoniques à tardi-tectoniques sont les équivalents plutoniques des «Dokhan Volcanics».Le terrain étudié se situe dans l'avant-pays plissé et charrié d'un orogène de marge continentale. Des ophiolites, particulièrement des serpentinites, affleurent le long de la surface de charriage entre le massif autochtone de Meatiq et la nappe complexe d'Abu Ziran.Des dômes, développés le long de deux géanticlinaux, ont été les centres d'une forte activité magmatique calco-alcaline associée, au moins, à une minéralisation aurifère.
: Meatiq Group ( ), Abu Ziran Group Hammamat Group ( ); - . , . , , , , , , . , Dokhan . Dokhan - - . . , , Meatiq Abu-Ziran.相似文献
73.
74.
Ali Aydin 《Pure and Applied Geophysics》2007,164(11):2329-2344
The Normalized Full Gradient (NFG) method which was put forward about 50 years ago has been used for downward continuation
of gravity potential data, especially in the former Union of Soviet Socialist Republics. This method nullifies perturbations
due to the passage of mass depth during downward continuation. The method depends on the downwards analytical continuation
of normalized full gradient values of gravity data. Analytical continuation discriminates certain structural anomalies which
cannot be distinguished in the observed gravity field. This method has been used in various petroleum and tectonic studies.
The Trapeze method was used for the determination of Fourier coefficients during the application of this method. No other
techniques for calculating these coefficients have been used. However, the Filon method was used for the determination of
Fourier coefficients during the application of the NFG method in this work. This method, rather than the Trapeze method, should
be preferred for indicating abnormal mass resources at the lower harmonics. In this study, the NFG method using the Filon
method has been applied the first time to theoretical models of gravity profiles as example field at the Hasankale-Horasan
petroleum exploration province where successful results were achieved. Hydrocarbon presence was shown on the NFG sections
by the application of NFG downward continuation operations on theoretical models. Important signs of hydrocarbon structure
on the NFG section for field and model data at low harmonics are obtained more effectively using this method. 相似文献
75.
Geotechnical properties of a chemically stabilized soil from Malaysia with rice husk ash as an additive 总被引:1,自引:0,他引:1
Summary The stabilization of Malaysian soil by mixing with rice husk ash, a locally available waste material, to improve its engineering properties is described. Stabilizing agents, i.e. cement and lime, were added to produce the reaction products which are responsible for the enhancement of the engineering properties. Based on the strength development, it seems that lime is the more effective stabilizing agent. However, the cheap waste material can be used as partial replacement for the more expensive cement in the cement-treatment of the soil. A durability study was carried out to evaluate the effectiveness of this stabilization method. 相似文献
76.
77.
78.
Babak Mohammadi Nguyen Thi Thuy Linh Ali Najah Ahmed Jana Vojteková Yiqing Guan 《水文科学杂志》2020,65(10):1738-1751
ABSTRACT Accurate runoff forecasting plays a key role in catchment water management and water resources system planning. To improve the prediction accuracy, one needs to strive to develop a reliable and accurate forecasting model for streamflow. In this study, the novel combination of the adaptive neuro-fuzzy inference system (ANFIS) model with the shuffled frog-leaping algorithm (SFLA) is proposed. Historical streamflow data of two different rivers were collected to examine the performance of the proposed model. To evaluate the performance of the proposed ANFIS-SFLA model, six different scenarios for the model input–output architecture were investigated. The results show that the proposed ANFIS-SFLA model (R2 = 0.88; NS = 0.88; RMSE = 142.30 (m3/s); MAE = 88.94 (m3/s); MAPE = 35.19%) significantly improved the forecasting accuracy and outperformed the classic ANFIS model (R2 = 0.83; NS = 0.83; RMSE = 167.81; MAE = 115.83 (m3/s); MAPE = 45.97%). The proposed model could be generalized and applied in different rivers worldwide. 相似文献
79.
The objective of the study was to determine which factors regulate zooplankton organisms along Lake Nasser. Temperature, pH, DO, conductivity, turbidity, nutrients, and zooplankton abundance were measured. Twenty-three species of zooplankton were recorded in Lake Nasser included in Copepoda, Cladocera and Rotifera. Copepoda represented the main bulk of the community. The lowest standing stock of zooplankton was noticed during spring due to the highest fish predation during this season associated with the lowest turbidity. Big difference in temperature in Lake Nasser along the year round is considered as a controlling factor related to range of tolerance of species. The oscillation of the lake water level and the different factors affect the standing stock of zooplankton in the lake. Thus, continuous monitoring of Lake Nasser biota should be undertaken to follow the changes in the ecosystem. 相似文献
80.
Organic Material and Trace Elements of Bituminous Rocks in the Ozank(?)y Field,Ankara,Turkey
下载免费PDF全文
![点击此处可从《《地质学报》英文版》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bituminous rocks in the Ozank(?)y(Ankara) field are different from those of the Paleocene- Eocene Mengen and Güineytepe(Bolu) regions in metal enrichment levels.Organic carbon(C_(org)) content of organic material-rich rocks in the Ozank(?)y(Ankara) field is 3.66-40.72% wt averaging 14.34%.The dominant organic materials are algae/amorphous accompanied by minor amount of herbaceous material(The dominant kerogen type is Type-Ⅰwith a limited amount of Type-Ⅱkerogen.). The bituminous rocks in the Ozank(?)y field are enriched in heavy metals such as Ni,Mn,As and Cr.In comparison with the average enrichment values of elements,Ni,Mn,As and Cr in bituminous shales of the Ozank(?)y field are as about 4.38,14.93,10.90 and 5.58 times as average values.The average concentrations of these heavy metals are also as high as 215×10~(-6),828×10~(-6),58.54×10~(-6),and 148×10~(-6) respectively.In addition,sorption properties of clay and organic materials are also important for metal enrichments in the bituminous shales. 相似文献