全文获取类型
收费全文 | 120篇 |
免费 | 11篇 |
专业分类
大气科学 | 11篇 |
地球物理 | 35篇 |
地质学 | 13篇 |
海洋学 | 9篇 |
天文学 | 60篇 |
自然地理 | 3篇 |
出版年
2024年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 3篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有131条查询结果,搜索用时 15 毫秒
71.
72.
By considering high-temperature (classical) thermal oscillations of atoms in certain simple crystal structures with purely central interatomic forces, the treatment of anharmonic oscillations is generalised to random three-dimensional motion, yielding the Vashchenko and Zubarev relationship for the Grüneisen ratio γ at any pressure. If one-dimensional atomic oscillations only are considered the equation reduces to the Dugdale-MacDonald expression. To account for non-central forces additional terms must be introduced, giving: where f = 0 for purely central forces. Calculations of f in terms of the Poisson ratio for different crystal structures have not been made, but for many materials the central-force approximation suffices. This is believed to be true both for the outer core and for the close-packed structures of the lower mantle . For the upper mantle non-central atomic forces are important and we have no estimate of ( independently of laboratory values for plausible minerals which suggest γ ≈ 0.8. 相似文献
73.
An experiment was set-up to investigate the adjustment of turbulence over a roughness transition (moorland to forest). Results from this experiment support the development of an internal boundary layer (IBL) at the transition, which propagates upwards by turbulent diffusion as a function of distance downwind from the transition. Spectra and length-scale results uphold the hypothesis that, over a transition to a rough surface, the variance distribution shifts towards smaller wavelengths/length scales. However, results suggest that the adjustment of streamwise velocity variance may be faster than the adjustment of the vertical velocity variance. The concept of an equilibrium layer developing above the new surface is supported. Fetch requirements for equilibrium are, however, found to differ between first order and second order (flux) statistics, with second order statistics requiring a longer fetch. Results indicate that fetch should exceed 25 times the height of the measurement above the zero plane, which is a 2° (±0.5) growth angle, for flux equilibrium. 相似文献
74.
75.
76.
Improved Vertical Streambed Flux Estimation Using Multiple Diurnal Temperature Methods in Series
下载免费PDF全文
![点击此处可从《Ground water》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Analytical solutions that use diurnal temperature signals to estimate vertical fluxes between groundwater and surface water based on either amplitude ratios (Ar) or phase shifts (Δ?) produce results that rarely agree. Analytical solutions that simultaneously utilize Ar and Δ? within a single solution have more recently been derived, decreasing uncertainty in flux estimates in some applications. Benefits of combined (ArΔ?) methods also include that thermal diffusivity and sensor spacing can be calculated. However, poor identification of either Ar or Δ? from raw temperature signals can lead to erratic parameter estimates from ArΔ? methods. An add‐on program for VFLUX 2 is presented to address this issue. Using thermal diffusivity selected from an ArΔ? method during a reliable time period, fluxes are recalculated using an Ar method. This approach maximizes the benefits of the Ar and ArΔ? methods. Additionally, sensor spacing calculations can be used to identify periods with unreliable flux estimates, or to assess streambed scour. Using synthetic and field examples, the use of these solutions in series was particularly useful for gaining conditions where fluxes exceeded 1 m/d. 相似文献
77.
78.
We report the first detection of the nitrogen sulfide (NS) radical in a comet. The abundance relative to water is at least a few hundredths of a percent for Comet Hale-Bopp. 相似文献
79.
Clément Duvert Adrià Barbeta Lindsay B. Hutley Leidy Rodriguez Dylan J. Irvine Andrew R. Taylor 《水文研究》2024,38(2):e15099
Cryogenic vacuum distillation (CVD) is a widely used technique for extracting plant water from stems for isotopic analysis, but concerns about potential isotopic biases have emerged. Here, we leverage the Cavitron centrifugation technique to extract xylem water and compare its isotopic signature to that of CVD-extracted bulk stem water as well as source water. Conducted under field conditions in tropical northern Australia, our study spans seven tree species naturally experiencing a range of water stress levels. Our findings reveal a significant deuterium bias in CVD-extracted bulk stem water when compared to xylem water (median bias −14.9‰), whereas xylem water closely aligned with source water (median offset −1.9‰). We find substantial variations in deuterium bias among the seven tree species (bias ranging from −19.3‰ to −9.1‰), but intriguingly, CVD-induced biases were unrelated to environmental factors such as relative stem water content and predawn leaf water potential. These results imply that inter-specific differences may be driven by anatomical traits rather than tree hydraulic functioning. Additionally, our data highlight the potential to use a site-specific deuterium offset, based on the isotopic signature of local source water, for correcting CVD-induced biases. 相似文献
80.
Upward discharge to surface water bodies can be quantified using analytical models based on temperature–depth (T-z) profiles. The use of sediment T-z profiles is attractive as discharge estimates can be obtained using point-in-time data that are collected inexpensively and rapidly. Previous studies have identified that T-z methods can only be applied at times of the year when there is significant difference between the streambed–water interface and deeper sediment temperatures (e.g., winter and summer). However, surface water temperatures also vary diurnally, and the influence of these variations on discharge estimates from T-z methods is poorly understood. For this study, synthetic T-z profiles were generated numerically using measured streambed interface temperature data to assess the influence of diurnal temperature variations on discharge estimation and provide insight into the suitable application of T-z methods. Results show that the time of day of data collection can have a substantial influence on vertical flux estimates using T-z methods. For low groundwater discharge fluxes (e.g., 0.1 m d−1), daily transience in streambed temperatures led to relatively large errors in estimated flow magnitude and direction. For higher discharge fluxes (1.5 m d−1), the influence of transient streambed temperatures on discharge estimates was strongly reduced. Discharge estimates from point-in-time T-z profiles were most accurate when the uppermost point in the T-z profile was near the bed interface daily mean (two time periods daily). Where temperature time series data are available, daily averaged T-z profiles can produce accurate discharge estimates across a wide range of discharge rates. Seasonality in shallow groundwater temperature generally had a negligible influence on vertical flow estimates. These findings can be used to plan field campaigns and provide guidance on the optimal application of T-z methods to quantify vertical groundwater discharge to surface water bodies. 相似文献