全文获取类型
收费全文 | 747篇 |
免费 | 108篇 |
国内免费 | 139篇 |
专业分类
测绘学 | 62篇 |
大气科学 | 71篇 |
地球物理 | 178篇 |
地质学 | 327篇 |
海洋学 | 114篇 |
天文学 | 57篇 |
综合类 | 48篇 |
自然地理 | 137篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 21篇 |
2019年 | 33篇 |
2018年 | 22篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 36篇 |
2014年 | 40篇 |
2013年 | 46篇 |
2012年 | 35篇 |
2011年 | 34篇 |
2010年 | 28篇 |
2009年 | 54篇 |
2008年 | 41篇 |
2007年 | 47篇 |
2006年 | 50篇 |
2005年 | 43篇 |
2004年 | 33篇 |
2003年 | 27篇 |
2002年 | 37篇 |
2001年 | 24篇 |
2000年 | 31篇 |
1999年 | 27篇 |
1998年 | 26篇 |
1997年 | 25篇 |
1996年 | 25篇 |
1995年 | 26篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有994条查询结果,搜索用时 15 毫秒
631.
A numerical model, called CCRS1, is presented for one‐dimensional large strain consolidation under constant rate of strain loading conditions. The algorithm accounts for vertical strain, general constitutive relationships, relative velocity of fluid and solid phases, changing compressibility and hydraulic conductivity during consolidation, and an externally applied hydraulic gradient acting across the specimen. Soil compressibility is rate independent, and as such, the current model is most appropriate for less‐structured clays. Verification checks show excellent agreement with analytical and numerical solutions for small and large strain conditions. A series of numeric examples indicates that compressibility and hydraulic conductivity constitutive relationships can have an important effect on constant rate of strain consolidation response. Results also indicate that analytical solutions obtained using small strain theory can be in significant error for large strain conditions with changing coefficient of consolidation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
632.
Harold Ritchie 《地球物理与天体物理流体动力学》2013,107(1-2):49-92
Abstract The behavior of Rossby waves on a shear flow in the presence of a nonlinear critical layer is studied, with particular emphasis on the role played by the critical layer in a Rossby wave resonance mechanism. Previous steady analyses are extended to the resonant case and it is found that the forced wave dominates the solution, provided the flow configuration is not resonant for the higher harmonics induced by the critical layer. Numerical simulations for the forced initial value problem show that the solution evolves towards the analysed steady state when conditions are resonant for the forced wave, and demonstrate some of the complications that arise when they are resonant for higher harmonics. In relating the initial value and steady problems, it is argued that the time dependent solution does not require the large mean flow distortion that Haberman (1972) found to be necessary outside the critical layer in the steady case. 相似文献
633.
The groutability depends on the properties of the grout, its injection processes, and on the mechanical properties of the soil formation. During the process of pouring cement‐based grouting into a porous medium, a variation with time occurs in the viscosity of grout suspension. In addition, the particle filtration phenomenon will limit the expansion of the grouted zone because cement particles are progressively stagnant within the soil matrix. In this paper, a closed‐form solution was derived by implementing the mass balance equations and the generalized phenomenological filtration law, which can be used to evaluate the deposition of cement‐based grout in the soil matrix. The closed‐form solution relevant to a particular spherical flow was modified by a step‐wise numerical calculation, considering the variable viscosity caused by a chemical reaction, and the decrease in porosity resulting from grout particle deposition in the soil pores. A series of pilot‐scale chamber injection tests was performed to verify that the developed step‐wise numerical calculation is able to evaluate the injectable volume of grout and the deposition of grout particles. The results of the chamber injection tests concurred well with that of the step‐wise numerical calculation. Based on the filtration phenomenon, a viable approach for estimating the groutability of cement‐based grout in a porous medium was also suggested, which might facilitate a new insight in the design of the grouting process. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
634.
Numerical models are systematically presented for time-dependent thermal convection of Newtonian fluid with strongly temperature-dependent viscosity in a two-dimensional rectangular box of aspect ratio 3 at various values of the Rayleigh number Rab defined with viscosity at the bottom boundary up to 1.6×108 and the viscosity contrast across the box rη up to 108. We found that there are two different series of bifurcations that take place as rη increases. One series of bifurcations causes changes in the behavior of the thermal boundary layer along the surface boundary from small-viscosity-contrast (SVC) mode, through transitional (TR) mode, to stagnant-lid (ST) mode, or from SVC mode directly to ST mode, depending on Rab. Another series of bifurcations causes changes in the aspect ratio of convection cells; convection with an elongated cell can take place at moderate rη (103–105.5 at Rab=6×106), while only convection of aspect ratio close to 1 takes place at small rη and large rη. The parameter range of rη and Rab for elongated-cell convection overlaps the parameter range for SVC and ST modes and include the entire parameter range for TR mode. In the elongated-ST regime, the lid of highly viscous fluid along the top boundary is not literally ‘stagnant’ but can horizontally move at a velocity high enough to induce a convection cell with aspect ratio much larger than 1. 相似文献
635.
Ground penetrating radar application in a shallow marine Oxfordian limestone sequence located on the eastern flank of the Paris Basin, NE France 总被引:5,自引:0,他引:5
Guy Dagallier Ari I. Laitinen Fabrice Malartre Ignace P. A. M. Van Campenhout Paul C. H. Veeken 《Sedimentary Geology》2000,130(3-4):149-165
A Ground Penetrating Radar (GPR) survey has been carried out in Upper Jurassic limestones located on the eastern flank of the Paris Basin (NE France). The potential of the investigation method is assessed for delineating geologically meaningful stratifications in the shallow subsurface. The fundamentals of the GPR technique are described. Penetration depth and vertical resolution depends on the soil conditions, the characteristics of input signal and the configuration of the transmitter–receiver assembly. In the studied carbonates the penetration level is rather good and the electromagnetic signal reaches up to 1000 nanoseconds maximum (i.e. approximately 55 m). Several depositional units are outlined on the GPR profiles. Six different lithological units are recognised with distinct GPR reflection characteristics. The profiles illustrate the internal 3D organisation of the carbonate platform and its geometry. They provide detailed insight into the nature of an Oxfordian reefal build-up. The high-resolution subsurface model is directly calibrated with geological field observations and it results in a predictive 3D depositional working model. The GPR method is a non-destructive remote sensing technique that is cost effective. The method is considered complementary to other conventional high-resolution reservoir characterisation studies. It represents a powerful investigation tool in earth science studies concerning the imaging of the structure of the shallow subsurface. 相似文献
636.
637.
地下水的pH值可在3~10的范围内变化,碳酸盐的溶解受地下水pH值的影响很大。本文从实验和理论上定量探讨了方解石、菱铁矿、菱镁矿、菱锌矿和重晶石在水中溶解度随pH的变化规律。笔者从溶度积常数出发,在考虑了金属离子和碳酸根的副反应及其活度系数的基础上,导出了一个计算溶解度的公式,给定不同pH值,就可用微机计算出该条件下的lgS~pH的溶解度曲线。实验证明:计算与实测溶解度曲线形状相同。 相似文献
638.
Shijie Zhong 《Geophysical Journal International》1996,124(1):18-28
639.
640.
This paper investigates the effects of the spatial variation of the cosmological constant λ on the spacetime geometry within
and outside a massive object. It is seen that the variation of λ with the radial coordinate introduces non-trivial changes
leading to spacetime closing on itself around a massive object. It may also be possible to generate interior solutions that
lead to flat rotation curves of galaxies 相似文献