全文获取类型
收费全文 | 557篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 47篇 |
地球物理 | 113篇 |
地质学 | 240篇 |
海洋学 | 27篇 |
天文学 | 87篇 |
综合类 | 1篇 |
自然地理 | 47篇 |
出版年
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 24篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 15篇 |
2009年 | 27篇 |
2008年 | 20篇 |
2007年 | 24篇 |
2006年 | 17篇 |
2005年 | 24篇 |
2004年 | 12篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 10篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1970年 | 3篇 |
1969年 | 6篇 |
排序方式: 共有567条查询结果,搜索用时 15 毫秒
81.
Wassim E. Tabet Amy B. Cerato Gerald A. Miller 《Geotechnical and Geological Engineering》2014,32(5):1253-1260
This paper presents results of the influence of clod size and initial moisture condition on the shearing behavior of a clayey soil with a plasticity index of 22. The clods were divided into different size categories, and then two groups of samples were prepared; samples with large clods (LC = clod size less than 38 mm) and samples with small clods (SC = clod size less than 4.75 mm). Two initial moisture conditions were achieved using two different moisture tempering times of 0 and 14 days. All samples were compacted to the same density and moisture content (95 % of maximum dry density and 2 % dry of optimum moisture content). Triaxial compression tests, including constant water content unsaturated tests and backpressure saturated, isotropically consolidated, undrained compression tests were performed at different confining pressures. At 0-day tempering time, samples prepared using large clods were found to be stiffer and stronger than those prepared using small clods. However, at 14-day tempering time, the strength of both LC and SC samples was similar. 相似文献
82.
Relative to those at sub‐bankfull flow, hydraulic conditions at overbank flow, whether in the channel or on the floodplain, are poorly understood. Here, velocity conditions are analysed over an unusually wide range of flows in the arid zone river of Cooper Creek with its complex system of anastomosing channels and large fluctuations in floodplain width. At‐a‐station hydraulic geometry relationships reveal sharp discontinuities in velocity at the inbank–overbank transition, the nature of the discontinuity varying with the degree of flow confinement and the level of channel–floodplain interaction. However, despite inter‐sectional differences, velocities remain modest throughout the flow range in this low‐gradient river, and the large increases in at‐a‐station discharge are principally accommodated by changes in cross‐sectional area. Velocity distribution plots suggest that within‐channel conditions during overbank flow are characterized by a central band of high velocity which penetrates far toward the bed, helping to maintain already deep cross‐sections. Floodplain resistance along Cooper Creek is concentrated at channel bank tops where vegetation density is highest, and the subsequent flow retardation is transmitted across the surface of the channels over distances as large as 50–70 m. The rough floodplain surface affects flood wave transmission, producing significant decreases in wave speeds downstream. The character of the wave‐speed–discharge relationship also changes longitudinally, from log–linear in the upper reaches to nonlinear where the floodplain broadens appreciably. The nonlinear form is similar in several respects to relationships proposed for more humid rivers, with flood wave speed reaching an intermediate maximum at about four‐fifths bankfull discharge before decreasing to a minimum at approximately Q2·33. It does not regain the value at the intermediate maximum until the 10 year flood, by which time floodplain depths have become relatively large and broad floodways more active. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
83.
Gerald D. Quinlan 《Celestial Mechanics and Dynamical Astronomy》1994,58(4):339-351
Techniques for reducing roundoff error are compared by testing them on high-order Störmer and summetric multistep methods. The best technique for most applications is to write the equation in summed, function-evaluation form and to store the coefficients as rational numbers. A larger error reduction can be achieved by writing the equation in backward-difference form and performing some of the additions in extended precision, but this entails a larger cpu cost. 相似文献
84.
Laurent Koechlin Denis Serre Gerald K. Skinner Peter Von Ballmoos Thomas Crouzil 《Experimental Astronomy》2005,20(1-3):307-315
The light deviation caused by the gravitational potential in the vicinity of the sun could be used as a means of focussing radiation that cannot be focussed easily otherwise. The gravitational lens formed by the sun is not stigmatic, but does have the advantage of being achromatic and acts identically on all types of mass-less radiations. For a source at infinity, its geometrical characteristics present a “caustic” line starting at 550 astronomical units (UA) downstream from the sun. In a plane perpendicular to that caustic line, images of distant objects are formed.The perturbations by the solar corona plasma will significantly blur electromagnetic radiation for wavelengths longer than those of the IR domain. At shorter wavelengths, for example the γ domain, the focussing process could lead to 108 amplification factors. In order to reach the regions where images are formed, long distance space missions are necessary. Once launched, missions of this type would be dedicated to a single field. Some possible targets are considered, such as Sagitarius A observed in X and γ rays.In this paper we study the point spread function (PSF) of the sun as a gravitational lens. Taking into account perturbations by the planets, the non sphericity of the sun and coronal plasma index, we derive limits within which such observations could be possible. 相似文献
85.
86.
87.
88.
89.
In this, the first of a short series of papers on the magnitudes of galaxies, the dependence of magnitude on the aperture used in photoelectric measures is discussed. mean results from an empirical study are presented. 相似文献
90.
System dynamics is a computer-aided approach to evaluating the interrelationships of different components and activities within complex systems. Recently, system dynamics models have been developed in areas such as policy design, biological and medical modeling, energy and the environmental analysis, and in various other areas in the natural and social sciences. The Idaho National Engineering and Environmental Laboratory, a multipurpose national laboratory managed by the Department of Energy, has developed a system dynamics model in order to evaluate its utility for modeling large complex hydrological systems. We modeled the Bear River basin, a transboundary basin that includes portions of Idaho, Utah, and Wyoming. We found that system dynamics modeling is very useful for integrating surface water and ground water data and for simulating the interactions between these sources within a given basin. In addition, we also found that system dynamics modeling is useful for integrating complex hydrologic data with other information (e.g., policy, regulatory, and management criteria) to produce a decision support system. Such decision support systems can allow managers and stakeholders to better visualize the key hydrologic elements and management constraints in the basin, which enables them to better understand the system via the simulation of multiple "what-if" scenarios. Although system dynamics models can be developed to conduct traditional hydraulic/hydrologic surface water or ground water modeling, we believe that their strength lies in their ability to quickly evaluate trends and cause-effect relationships in large-scale hydrological systems, for integrating disparate data, for incorporating output from traditional hydraulic/hydrologic models, and for integration of interdisciplinary data, information, and criteria to support better management decisions. 相似文献