全文获取类型
收费全文 | 283篇 |
免费 | 16篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 12篇 |
地球物理 | 110篇 |
地质学 | 133篇 |
海洋学 | 17篇 |
天文学 | 8篇 |
综合类 | 3篇 |
自然地理 | 10篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 14篇 |
2018年 | 36篇 |
2017年 | 26篇 |
2016年 | 31篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 24篇 |
2012年 | 21篇 |
2011年 | 27篇 |
2010年 | 15篇 |
2009年 | 11篇 |
2008年 | 4篇 |
2007年 | 1篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2002年 | 2篇 |
2001年 | 1篇 |
1995年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1984年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有307条查询结果,搜索用时 15 毫秒
1.
In the design process of berm breakwaters, their front slope recession has an inevitable rule in large number of model tests, and this parameter being studied. This research draws its data from Moghim’s and Shekari’s experiment results. These experiments consist of two different 2D model tests in two wave flumes, in which the berm recession to different sea state and structural parameters have been studied. Irregular waves with a JONSWAP spectrum were used in both test series. A total of 412 test results were used to cover the impact of sea state conditions such as wave height, wave period, storm duration and water depth at the toe of the structure, and structural parameters such as berm elevation from still water level, berm width and stone diameter on berm recession parameters. In this paper, a new set of equations for berm recession is derived using the M5'' model tree as a machine learning approach. A comparison is made between the estimations by the new formula and the formulae recently given by other researchers to show the preference of new M5'' approach. 相似文献
2.
This paper presents a new procedure for the optimization of the mooring design of floating platforms, in which an automatic design sequence is also established. Regarding the optimization philosophy, the following aspects are dealt with:
- • The optimization of the platform heading and its mooring pattern, taking into account the environmental force spreading;
- • optimum line length or line tension for each mooring line, associated to the optimization of the mooring line materials and sizes.
3.
Nelly Mouawad Matthew H. Burger Andrew E. Potter Ronald J. Vervack Jr. Mehdi Benna 《Icarus》2011,211(1):21-36
We have used observations of sodium emission obtained with the McMath-Pierce solar telescope and MESSENGER’s Mercury Atmospheric and Surface Composition Spectrometer (MASCS) to constrain models of Mercury’s sodium exosphere. The distribution of sodium in Mercury’s exosphere during the period January 12-15, 2008, was mapped using the McMath-Pierce solar telescope with the 5″ × 5″ image slicer to observe the D-line emission. On January 14, 2008, the Ultraviolet and Visible Spectrometer (UVVS) channel on MASCS sampled the sodium in Mercury’s anti-sunward tail region. We find that the bound exosphere has an equivalent temperature of 900-1200 K, and that this temperature can be achieved if the sodium is ejected either by photon-stimulated desorption (PSD) with a 1200 K Maxwellian velocity distribution, or by thermal accommodation of a hotter source. We were not able to discriminate between the two assumed velocity distributions of the ejected particles for the PSD, but the velocity distributions require different values of the thermal accommodation coefficient and result in different upper limits on impact vaporization. We were able to place a strong constraint on the impact vaporization rate that results in the release of neutral Na atoms with an upper limit of 2.1 × 106 cm−2 s−1. The variability of the week-long ground-based observations can be explained by variations in the sources, including both PSD and ion-enhanced PSD, as well as possible temporal enhancements in meteoroid vaporization. Knowledge of both dayside and anti-sunward tail morphologies and radiances are necessary to correctly deduce the exospheric source rates, processes, velocity distribution, and surface interaction. 相似文献
4.
5.
6.
The role of tourism in rural development: Evidence from Iran 总被引:1,自引:0,他引:1
Nooripoor Mehdi Khosrowjerdi Madineh Rastegari Hamid Sharifi Zeinab Bijani Masoud 《GeoJournal》2021,86(4):1705-1719
GeoJournal - Tourism can play an important role in diversifying the rural economy and its expanding in rural areas contributes to the sustainability of the population and the economy of these areas... 相似文献
7.
Mehdi Zeidouni Jean-Philippe Nicot Susan D. Hovorka 《Environmental Earth Sciences》2014,72(5):1733-1747
CO2 injection in saline aquifers induces temperature changes owing to processes such as Joule–Thomson cooling, endothermic water vaporization, exothermic CO2 dissolution besides the temperature discrepancy between injected and native fluids. CO2 leaking from the injection zone, in addition to initial temperature contrast due to the geothermal gradient, undergoes similar processes, causing temperature changes in the above zone. Numerical simulation tools were used to evaluate temperature changes associated with CO2 leakage from the storage aquifer to an above-zone monitoring interval and to assess the monitorability of CO2 leakage on the basis of temperature data. The impact of both CO2 and brine leakage on temperature response is considered for three cases (1) a leaky well co-located with the injection well, (2) a leaky well distant from the injector, and (3) a leaky fault. A sensitivity analysis was performed to determine key operational and reservoir parameters that control the temperature signal in the above zone. Throughout the analysis injection-zone parameters remain unchanged. Significant pressure drop upon leakage causes expansion of CO2 associated with Joule–Thomson cooling. However, brine may begin leaking before CO2 breakthrough at the leakage pathway, causing heating in the above zone. Thus, unlike the pressure which increases in response to both CO2 and brine leakage, the temperature signal may differentiate between the leaking fluids. In addition, the strength of the temperature signal correlates with leakage velocity unlike pressure signal whose strength depends on leakage rate. Increasing leakage conduit cross-sectional area increases leakage rate and thus increases pressure change in the above zone. However, it decreases leakage velocity, and therefore, reduces temperature cooling and signal. It is also shown that the leakage-induced temperature change covers a small area around the leakage pathway. Thus, temperature data will be most useful if collected along potential leaky wells and/or wells intersecting potential leaky faults. 相似文献
8.
9.
A detailed multiscale analysis is presented of the swelling phenomenon in unsaturated clay-rich materials in the linear regime through homogenization. Herein, the structural complexity of the material is formulated as a three-scale, triple porosity medium within which microstructural information is transmitted across the various scales, leading ultimately to an enriched stress-deformation relation at the macroscopic scale. As a side note, such derived relationship leads to a tensorial stress partitioning that is reminiscent of a Terzaghi-like effective stress measure. Otherwise, a major result that stands out from previous works is the explicit expression of swelling stress and capillary stress in terms of micromechanical interactions at the very fine scale down to the clay platelet level, along with capillary stress emerging due to interactions between fluid phases at the different scales, including surface tension, pore size, and morphology. More importantly, the swelling stress is correlated with the disjoining forces due to electrochemical effects of charged ions on clay minerals and van der Waals forces at the nanoscale. The resulting analytical expressions also elucidate the role of the various physics in the deformational behavior of clayey material. Finally, the capability of the proposed formulation in capturing salient behaviors of unsaturated expansive clays is illustrated through some numerical examples. 相似文献
10.
Mehdi Khorasanipour Majid H. Tangestani Reza Naseh Hamid Hajmohammadi 《Applied Geochemistry》2011,26(5):714-730
The Sarcheshmeh is one of the largest Oligo-Miocene porphyry Cu deposits in the world. Comparative hydrochemical, mineralogical and chemical fractionation associated with mining efflorescence salts and processing wastes of this mine are discussed. Hydrochemical results showed that rock waste dumps, reject wastes and old impoundments of tailings are the main sources of acid mine drainage waters (AMD) that contain potentially toxic metals such as Cd, Co, Cu, Mn, Ni and Zn as well as Al. Episodic fluxes of highly contaminated acidic waters were produced in a tailings dam over a short period of time. Secondary soluble minerals provide important controls on the quality of AMD produced, especially in old, dry tailings impoundments. Secondary sulfate minerals such as gypsum, magnesiocopiapite, hydronium jarosite, kornelite and coquimbite were found in rock waste drainages and in old weathered reject wastes. Highly soluble secondary minerals such as gypsum, eriochalcite, and bonattite are also observed in an evaporative layer on old tailings impoundments. Chemical fractionation patterns of potentially toxic elements showed that the geochemical behavior of metals is primarily controlled by the mineralogical composition of waste samples. Elements such as Co, Cr, Cu, Mn, Ni and Zn are readily released into the water soluble fraction from efflorescence salts associated with rock waste drainages, as well as from the evaporative layer of old tailings. Potentially toxic elements, such as As, Mo and Pb, are principally adsorbed or co-precipitated with amorphous and crystalline Fe oxides, but they may also be associated with oxidizing, primary sulfides and residual fractions. Following the development of the dammed tailings pond, the secondary minerals were dissolved, producing acidic waters contaminated by Al (154 mg L−1), Cu (150 mg L−1), Cd (0.31 m gL−1), Co (2.13 mg L−1), Mn (73.7 mg L−1), Ni (1.74 mg L−1), Zn (20.3 mg L−1) and Cl (1690 mg L−1). Therefore, the potential use of recycled water from the Sarcheshmenh dammed tailings pond is diminished by the presence of corrosive ions like Cl− in highly acidic fluids that promote corrosion of pipes and pumps in the water recycling system. 相似文献