全文获取类型
收费全文 | 4986篇 |
免费 | 608篇 |
国内免费 | 893篇 |
专业分类
测绘学 | 420篇 |
大气科学 | 867篇 |
地球物理 | 1103篇 |
地质学 | 2196篇 |
海洋学 | 449篇 |
天文学 | 592篇 |
综合类 | 336篇 |
自然地理 | 524篇 |
出版年
2024年 | 13篇 |
2023年 | 53篇 |
2022年 | 153篇 |
2021年 | 188篇 |
2020年 | 148篇 |
2019年 | 154篇 |
2018年 | 222篇 |
2017年 | 217篇 |
2016年 | 267篇 |
2015年 | 204篇 |
2014年 | 260篇 |
2013年 | 310篇 |
2012年 | 304篇 |
2011年 | 307篇 |
2010年 | 284篇 |
2009年 | 333篇 |
2008年 | 266篇 |
2007年 | 277篇 |
2006年 | 223篇 |
2005年 | 218篇 |
2004年 | 189篇 |
2003年 | 173篇 |
2002年 | 150篇 |
2001年 | 173篇 |
2000年 | 162篇 |
1999年 | 148篇 |
1998年 | 175篇 |
1997年 | 152篇 |
1996年 | 123篇 |
1995年 | 96篇 |
1994年 | 117篇 |
1993年 | 82篇 |
1992年 | 74篇 |
1991年 | 53篇 |
1990年 | 35篇 |
1989年 | 30篇 |
1988年 | 34篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 7篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有6487条查询结果,搜索用时 31 毫秒
1.
Assessment of alternative adsorption models and global sensitivity analysis to characterize hexavalent chromium loss from soil to surface runoff
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigate our ability to assess transfer of hexavalent chromium, Cr(VI), from the soil to surface runoff by considering the effect of coupling diverse adsorption models with a two‐layer solute transfer model. Our analyses are grounded on a set of two experiments associated with soils characterized by diverse particle size distributions. Our study is motivated by the observation that Cr(VI) is receiving much attention for the assessment of environmental risks due to its high solubility, mobility, and toxicological significance. Adsorption of Cr(VI) is considered to be at equilibrium in the mixing layer under our experimental conditions. Four adsorption models, that is, the Langmuir, Freundlich, Temkin, and linear models, constitute our set of alternative (competing) mathematical formulations. Experimental results reveal that the soil samples characterized by the finest grain sizes are associated with the highest release of Cr(VI) to runoff. We compare the relative abilities of the four models to interpret experimental results through maximum likelihood model calibration and four model identification criteria (i.e., the Akaike information criteria [AIC and AICC] and the Bayesian and Kashyap information criteria). Our study results enable us to rank the tested models on the basis of a set of posterior weights assigned to each of them. A classical variance‐based global sensitivity analysis is then performed to assess the relative importance of the uncertain parameters associated with each of the models considered, within subregions of the parameter space. In this context, the modelling strategy resulting from coupling the Langmuir isotherm with a two‐layer solute transfer model is then evaluated as the most skilful for the overall interpretation of both sets of experiments. Our results document that (a) the depth of the mixing layer is the most influential factor for all models tested, with the exception of the Freundlich isotherm, and (b) the total sensitivity of the adsorption parameters varies in time, with a trend to increase as time progresses for all of the models. These results suggest that adsorption has a significant effect on the uncertainty associated with the release of Cr(VI) from the soil to the surface runoff component. 相似文献
2.
Barley(Hordeum vulgare L.) is one of the earliest domesticated crop species and ranked as the fourth largest cereal production worldwide. Forward genetic studies in barley have greatly advanced plant genetics during the last century; however, most genes are identified by the conventional mapping method. Array genotyping and exome-capture sequencing have also been successfully used to target the causal mutation in barley populations, but these techniques are not widely adopted because of associated costs and partly due to the huge genome size of barley. This review summarizes three mapping cases of barley cuticle mutants in our laboratory with the help of RNA-sequencing. The causal mutations have been successfully identified for two of them and the target genes are located in the pericentromeric regions. Detailed information on the mapping-by-sequencing, mapping-and-sequencing, and RNA-sequencing assisted linkage mapping are presented and some limitations and challenges on the mapping assisted by RNA sequencing are also discussed. The alternative and elegant methods presented in this review may greatly accelerate forward genetics of barley mapping, especially for laboratories without large funding. 相似文献
3.
4.
5.
6.
A formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
7.
8.
Stress wave attenuation across fractured rock masses is a great concern of underground structure safety. When the wave amplitude is large, fractures experience nonlinear deformation during the wave propagation. This paper presents a study on normal transmission of P‐wave across parallel fractures with nonlinear deformational behaviour (static Barton–Bandis model). The results show that the magnitude of transmission coefficient is a function of incident wave amplitude, nondimensional fracture spacing and number of fractures. Two important indices of nondimensional fracture spacing are identified, and they divide the area of nondimensional fracture spacing into three parts (individual fracture area, transition area and small spacing area). In the different areas, the magnitude of transmission coefficient has different trends with nondimensional fracture spacing and number of fractures. In addition, the study reveals that under some circumstances, the magnitude of transmission coefficient increases with increasing number of fractures, and is larger than 1. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
9.
10.
Microwave Type III bursts with positive frequency drifting rate were found by Stahli and Benz (1987) for first time. Type III events are especially interesting because they are well-known to be signatures of electron beams in coronal plasma, and they are effective means for diagnosting of source plasma. A microwave burst consisting of some microwave type III burst groups was registered at Beijing Astronomical Observatory with the 2545–2645–2840 MHz synchronous observing system. The distributions of frequency drifting rate, half power duration, and intensity for each impulse in the groups have been statistically analysed. From this analysis, some important parameters for the dynamic process in the flare are deduced and discussed. 相似文献