全文获取类型
收费全文 | 304篇 |
免费 | 18篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 42篇 |
地球物理 | 137篇 |
地质学 | 81篇 |
海洋学 | 17篇 |
天文学 | 26篇 |
自然地理 | 17篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 13篇 |
2013年 | 23篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 19篇 |
2009年 | 18篇 |
2008年 | 20篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 3篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 14篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1970年 | 1篇 |
1954年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有327条查询结果,搜索用时 15 毫秒
71.
This paper describes a stochastic analysis of steady state flow in a bounded, partially saturated heterogeneous porous medium subject to distributed infiltration. The presence of boundary conditions leads to non-uniformity in the mean unsaturated flow, which in turn causes non-stationarity in the statistics of velocity fields. Motivated by this, our aim is to investigate the impact of boundary conditions on the behavior of field-scale unsaturated flow. Within the framework of spectral theory based on Fourier–Stieltjes representations for the perturbed quantities, the general expressions for the pressure head variance, variance of log unsaturated hydraulic conductivity and variance of the specific discharge are presented in the wave number domain. Closed-form expressions are developed for the simplified case of statistical isotropy of the log hydraulic conductivity field with a constant soil pore-size distribution parameter. These expressions allow us to investigate the impact of the boundary conditions, namely the vertical infiltration from the soil surface and a prescribed pressure head at a certain depth below the soil surface. It is found that the boundary conditions are critical in predicting uncertainty in bounded unsaturated flow. Our analytical expression for the pressure head variance in a one-dimensional, heterogeneous flow domain, developed using a nonstationary spectral representation approach [Li S-G, McLaughlin D. A nonstationary spectral method for solving stochastic groundwater problems: unconditional analysis. Water Resour Res 1991;27(7):1589–605; Li S-G, McLaughlin D. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour Res 1995; 31(3):541–51], is precisely equivalent to the published result of Lu et al. [Lu Z, Zhang D. Analytical solutions to steady state unsaturated flow in layered, randomly heterogeneous soils via Kirchhoff transformation. Adv Water Resour 2004;27:775–84]. 相似文献
72.
73.
现在岩石学、矿床学的实验一般用样品是几十毫克、甚至十几毫克,其目的是要精确化。但是许多事实说明,这种精密的实验工作并不能完全解决矿床的成因。要解决矿床成因的问题,至少必须回答下面三个问题:(1)有用金属矿物是在什么条件下形成的;(2)有用金属矿物是如何富集为矿石的;(3)矿石如何具有一定的量,并达到经济上可开采的要求。实验岩石学和实验矿床学的资料一般只说明了第一个问题。 相似文献
74.
地质工作者研究矿床的意义,不仅在于认识矿床的形成与组成,不仅在于说明矿床的存在状况,还在于深入矿床的本质,指出找矿预测的途径;结合生产斗争实践,为社会主义革命和社会主义建设服务。 相似文献
75.
Tyan Yeh 《Solar physics》1985,95(1):83-97
An extraneous magnetized body, either a flux tube or a plasmoid, immersed in the solar atmosphere is subjected to a hydromagnetic buoyancy force. It results from the peripheral inhomogeneity of ambient hydromagnetic pressure, which is caused or enhanced by the presence of the extraneous body. This extra-caused force acts at various mass elements of the immersed body through its distribution as a nearly uniform force density, just like the gravitational force. Since hydromagnetic buoyancy force comprises hydrostatic buoyancy force, hydrodynamic lift force, and magnetostatic diamagnetic force, this constitutes a magnetohydrodynamic generalization of Archimedes' principle which deals with hydrostatic buoyancy force.In the solar atmosphere hydromagnetic buoyancy force has an obliquely upward direction, with a component in the direction opposite to the downward gravity. It provides an upward force to counterbalance or even to exceed the downward gravitational force. Such an upward force is the dynamic cause for the stationary equilibrium of quiescent prominences and outward motion of coronal transients. 相似文献
76.
In an aquifer, heterogeneity plays an important role in governing groundwater flow. Hence, aquifer characterization should involve both the pattern and values of the hydrogeological parameters. A new analytical solution describing the one-dimensional groundwater flow in a multi-zone unconfined aquifer is presented, and a methodology developed from the analytical solution and a heuristic approach for determining the pattern and values of the aquifer parameters are proposed. The analytical solution demonstrates that the hydraulic head varies spatially and is influenced by aquifer heterogeneity. Simulated annealing, a heuristic approach, is incorporated with the solution to simultaneously identify the pattern and values of the hydraulic conductivity for a horizontal multi-zone unconfined aquifer. This approach may be used to give an approximate result for a two-dimensional problem by dividing the model area into a number of transects along the transverse direction, identifying the parameter values along the longitudinal direction for each transect, and then smoothing the identified results. 相似文献
77.
Summary In microwave radiative transfer model simulations of atmospheric convective systems, the Mie calculations usually consume the majority of the computer time necessary for the calculations (70 to 90% for frequencies ranging from 6 to 300 GHz). For a large array of atmospheric profiles, the repeated Mie scattering calculations make the radiative transfer modeling not only expensive, but often impossible. A set of Mie tables, therefore, is developed to replace the actual Mie calculations in the microwave radiation model.The tables are divided into categories of liquid water (cloud water and rain), ice, snow, graupel and hail. The tables are free from restriction on variation of size distribution, particle density and mixing phases. Results from this study show that by using the Mie tables, the total CPU time is reduced by at least one order of magnitude, depending on the frequency. Compared to using full Mie calculation in the radiative model, the bias and root-mean-square (rms) deviation from the Mie tables are less than 1.2 K for any atmosphere with precipitation rates up to 125 mm hr–1 at any frequency and any viewing angle.The Mie tables are particularly useful in simulating the microwave radiation field over a mesoscale meteorological system. Such a study would not be satisfactory using a Mie parameterization scheme, because one would have to trade off the accuracy and flexibility for modeling efficiency.With 7 FiguresThis research was done under contract at the Goddard Space Flight Center, Greenbelt, Maryland. 相似文献
78.
Jinge Wang Aijun Su Wei Xiang Hsin-Fu Yeh Chengren Xiong Zongxing Zou Cheng Zhong Qingbing Liu 《Landslides》2016,13(4):795-804
The original Badong County, Hubei, China, was mainly below the highest water level of the Three Gorges Reservoir, which is 175 m above sea level. The new downtown of Badong was rebuilt in the Huangtupo area between 1982 and 1991. After detailed geological investigation in the Huangtupo area, four independent landslides were identified, making it one of the largest and most harmful landslide group in the Three Gorges Reservoir area. Since 2003, abundant data have been obtained from the Huangtupo No. 1 sliding mass about rainfall, water level, earth surface deformation and deep deformation. The monitoring data indicate that the earth surface and deep deformation of this landslide is closely related to the seasonal rainfall and water level fluctuation of the reservoir. During increases in the water level, the earth surface deformation velocity decreases, and then increases obviously in the subsequent water level decreasing stage. Because the water level drawdown period overlaps with the rainy season in this area, the earth surface deformation is affected by both rainfall and water level. The deformation velocity of the earth surface caused by rainfall is about 5 mm/month, while that caused by water level decrease is 5–7 mm/month. On the contrary, the deformation velocity of the deep sliding mass accelerates 2 to 3 times faster than average during water level increase. The distinction of surface and deep deformation regulations indicates that the effects of seasonal rainfall and water level fluctuation on the stability of reservoir wading landslides are different. Based on all monitoring data, we also found that the Huangtupo No. 1 riverside sliding mass is creeping seasonally during the seasonal rainfall and periodic reservoir water level fluctuation. The deformation velocities of the east regions of the sliding body indicate acceleration, making these regions even more dangerous. 相似文献
79.
A global navigation satellite system augmentation system availability analysis tool has been developed to simulate a ground-based augmentation system (GBAS) prototype, an integrity monitor test bed, to evaluate its operational benefits at an airport of interest. The proposed availability simulation tool includes all GBAS ground facility algorithms as well as a graphical user interface that allows the user to modify simulation options and parameters. The output of the simulation tool is presented in a Stanford chart to help visualize the performance. The chart indicates the availability and integrity. The performance is evaluated primarily in the vertical position domain because of the weaker satellite geometry and more stringent required navigation performance as compared to those of the horizontal position domain. The simulation tool is implemented in Qt (http://www.qt.io/), an open-source cross-platform toolkit, allowing the tool to run on various devices. The computations are performed in the associated C++ code. The Newark Liberty International Airport (ICAO code: KEWR) is used as a simulation example to demonstrate the utility of the developed tool for investigating how reduced error models impact GBAS availability at the airport. 相似文献
80.
Total sea surface temperature (SST) in a coupled GCM is diagnosed by separating the variability into signal variance and noise
variance. The signal and the noise is calculated from multi-decadal simulations from the COLA anomaly coupled GCM and the
interactive ensemble model by assuming both simulations have a similar signal variance. The interactive ensemble model is
a new coupling strategy that is designed to increase signal to noise ratio by using an ensemble of atmospheric realizations
coupled to a single ocean model. The procedure for separating the signal and the noise variability presented here does not
rely on any ad hoc temporal or spatial filter. Based on these simulations, we find that the signal versus the noise of SST
variability in the North Pacific is significantly different from that in the equatorial Pacific. The noise SST variability
explains the majority of the total variability in the North Pacific, whereas the signal dominates in the deep tropics. It
is also found that the spatial characteristics of the signal and the noise are also distinct in the North Pacific and equatorial
Pacific. 相似文献