全文获取类型
收费全文 | 6754篇 |
免费 | 1271篇 |
国内免费 | 1604篇 |
专业分类
测绘学 | 686篇 |
大气科学 | 1153篇 |
地球物理 | 1491篇 |
地质学 | 3274篇 |
海洋学 | 992篇 |
天文学 | 283篇 |
综合类 | 727篇 |
自然地理 | 1023篇 |
出版年
2024年 | 33篇 |
2023年 | 97篇 |
2022年 | 260篇 |
2021年 | 364篇 |
2020年 | 288篇 |
2019年 | 321篇 |
2018年 | 349篇 |
2017年 | 342篇 |
2016年 | 385篇 |
2015年 | 317篇 |
2014年 | 466篇 |
2013年 | 484篇 |
2012年 | 437篇 |
2011年 | 457篇 |
2010年 | 473篇 |
2009年 | 447篇 |
2008年 | 412篇 |
2007年 | 432篇 |
2006年 | 362篇 |
2005年 | 289篇 |
2004年 | 213篇 |
2003年 | 180篇 |
2002年 | 171篇 |
2001年 | 189篇 |
2000年 | 202篇 |
1999年 | 262篇 |
1998年 | 180篇 |
1997年 | 199篇 |
1996年 | 159篇 |
1995年 | 152篇 |
1994年 | 137篇 |
1993年 | 124篇 |
1992年 | 102篇 |
1991年 | 76篇 |
1990年 | 36篇 |
1989年 | 31篇 |
1988年 | 45篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 20篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1958年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有9629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
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.
Zhi Xu Cheng Fang Wei-Qun Can Astronomy Department of Nanjing University Nanjing Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2005,5(5):519-530
Chromospheric lines, including Ha, Lyα, Lyβand CaⅡK, CaⅡ8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyαline calculation and a smaller intensity enhancement in the Ha line-centers is found than in the previous results of Fang et al. 相似文献
3.
4.
海岩的长篇小说《河流如血》再创出版高记录,但作家仍局限于特有的小说叙述模式,这部作品设能做到相应的创新。概言之,模式第一面是“刑侦+恋爱”;模式第二面是“财子+佳人”;模式第三面是“道德+法制”。文学创作需要不断创新,创新的过程也是对创作模式的不断突破过程。作家应该警惕的是,不要让模式成为创作的桎梏。 相似文献
5.
为建立社会主义市场经济的地矿工作新秩序,本文对国有地矿企业的经营者(厂长、经理)这一特殊群体进行了分析。着重研究了新形势下企业经营者实行年薪制的问题。指出年薪制就是以企业一个生产经营周期为单位确定经营者的报酬,这一周期通常为一年。进而阐述了为什么要实行企业经营者年薪制;企业经营者的收入应与职工工资完全脱钩;采用基础报酬加效益报酬的方法确定收入等等。并构想了实行经营者年薪制所需要的外部环境:建立经营者人才市场、经营者要能进能出、实行任职资格制度、建立风险机制、按劳动力市场经济规律办事。 相似文献
6.
Tidal effects on temperature front in the Yellow Sea 总被引:5,自引:0,他引:5
Temperature front (TF) is one of the important features in the Yellow Sea, which forms in spring, thrives in summer, and fades
in autumn as thermocline declines. TF intensity ⋎S
T
⋎ is defined to describe the distribution of TF. Based on the MASNUM wave-tide-circulation coupled model, temperature distribution
in the Yellow Sea was simulated with and without tidal effects. Along 36°N, distribution of TF from the simulated results
are compared with the observations, and a quantitative analysis is introduced to evaluate the tidal effects on the forming
and maintaining processes of the TF. Tidal mixing and the circulation structure adapting to it are the main causes of the
TF.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献
7.
PALEOSOLSOFSANDYLANDSANDENVIRONMENTALCHANGESINTHEWESTERNPARTOFNORTHEASTPLAINOFCHINAWESTERNDURINGHOLOCENE¥QiuShanwen(裘善文)LiQus... 相似文献
8.
从ROSAT巡天和定点观测结果的对比出发,发现了几个低银纬的巡天源表中的X射线源在定点观测中没有出现.本文计算了在这些位置的定点观测中出现点源的流强上限,发现比巡天源表中这些源的流强值低很多,这表明它们的流强变化很大,可能是X射线双星系统中的一类———X射线暂现源. 相似文献
9.
In this paper, two factors — the redistribution of the density and the variation in the angular velocity of the Earth rotation, that affect the adopted value of the flattening for equidensity surface within the Earth, are discussed. The computational results show that the contribution of the redistribution of the density in the Earth interior (especially in the core) on the change of the flattening at the core-mantle boundary (CMB) is marginal, and that the calculated value of the flattening at the CMB can be in good agreement with the VLBI observed value so long as the fact that the angular velocity of the Earth rotation has undergone the tidal evolution is taken into account. As a result, this paper presents a set of recommended values of the dynamical parameters of the Earth (see Table III) for computing Earth's forced nutation series. 相似文献
10.