全文获取类型
收费全文 | 3604篇 |
免费 | 195篇 |
国内免费 | 283篇 |
专业分类
化学 | 1371篇 |
晶体学 | 13篇 |
力学 | 707篇 |
综合类 | 28篇 |
数学 | 250篇 |
物理学 | 1713篇 |
出版年
2024年 | 2篇 |
2023年 | 27篇 |
2022年 | 125篇 |
2021年 | 126篇 |
2020年 | 190篇 |
2019年 | 143篇 |
2018年 | 147篇 |
2017年 | 174篇 |
2016年 | 242篇 |
2015年 | 192篇 |
2014年 | 162篇 |
2013年 | 200篇 |
2012年 | 153篇 |
2011年 | 204篇 |
2010年 | 130篇 |
2009年 | 154篇 |
2008年 | 158篇 |
2007年 | 184篇 |
2006年 | 197篇 |
2005年 | 157篇 |
2004年 | 162篇 |
2003年 | 156篇 |
2002年 | 129篇 |
2001年 | 108篇 |
2000年 | 76篇 |
1999年 | 58篇 |
1998年 | 63篇 |
1997年 | 54篇 |
1996年 | 26篇 |
1995年 | 42篇 |
1994年 | 33篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有4082条查询结果,搜索用时 15 毫秒
121.
The migration of a downsized crescent-shaped dune was investigated in a wind tunnel experiment.Quantified upwind influx and vertical oscillation of the sand bed were introduced to modulate the saturation level of the sand flux above the dune surface to affect dune evolution.The evolution was recorded by top-view photography and then abstracted as the evolution of self-defined characteristic quantities using a digital image processing algorithm.The results showed that,in contrast to the case for spanwise quantities,the evolution of streamwise quantities corresponds to a linear increase in the modulation magnitude more positively and in a monotonic and convergent manner.In contrast with quantities on the windward face,the changes in quantities with respect to the horns were nonmonotonic with time and almost uncorrelated with the variation in modulation strength,which reveals the distinctiveness of leeside evolution. 相似文献
122.
123.
Sliced Latin hypercube designs are very useful for running a computer model in batches, ensembles of multiple computer models, computer experiments with qualitative and quantitative factors, cross-validation and data pooling. However, the presence of highly correlated columns makes the data analysis intractable. In this paper, a construction method for sliced (nearly) orthogonal Latin hypercube designs is developed. The resulting designs have flexible sizes and most are new. With the orthogonality or near orthogonality being guaranteed, the space-filling property of the resulting designs is also improved. Examples are provided for illustrating the proposed method. 相似文献
124.
125.
Magnetic‐based picolinaldehyde–melamine copper complex for the one‐pot synthesis of hexahydroquinolines via Hantzsch four‐component reactions
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A picolinaldehyde–melamine copper complex was loaded on a magnetic Fe3O4 core, so that it contained 0.33 mmol of Cu per gram, and was used as an efficient catalyst. The as‐synthesized catalyst was characterized using various techniques, including Fourier transform infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry and thermogravimetric analysis. The catalyst was used to activate the raw materials in the synthesis of hexahydroquinoline derivatives in one‐pot four‐component reactions. Low reaction time (minutes versus half an hour), solvent‐free condition and magnetically separable catalyst are some salient features of the developed catalyst. Also, the optimum amount of catalyst and temperature were determined as 0.07 g and 87.6 °C, respectively, which were obtained using response surface methodology and optimization techniques. 相似文献
126.
Polymer brushes have been widely used as functional surface coatings for broad applications including antifouling, energy storage, and lubrications. Understanding the molecule dynamics at polymer brush interfaces is important in unraveling the structure–property relationships in these materials and establishing a new materials design paradigm of novel functional polymer thin films with efficient interfacial transport. By applying modern fluorescence‐based single‐molecule spectroscopic and microscopic techniques, molecule dynamics at varied polymer brush interfaces have been experimentally investigated in recent years. New insights are given to the understandings of some unique and unusual materials properties of polymer brush thin films. This review summarizes some recent studies of molecular diffusion at polymer brush interfaces, highlights some new understandings of the interfacial properties of polymer brushes, and discusses future research opportunities in this field. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 85–103 相似文献
127.
结合新课标要求,揭示塑料薄膜撕扯实验在聚合物教学中的重要性、必要性。通过教学片段设计,发展学生“宏观辨识与微观探析、证据推理与模型认知”化学学科核心素养,并让学生认识物质的性能不仅取决于结构,也取决于生产工艺。并对人教版初、高中化学教材和教参中相关问题展开讨论和解释,以期更好地服务教学。 相似文献
128.
J. Christopher 《哲学杂志》2013,93(26):2992-3016
The flow and work-hardening behaviour of tempered martensitic P92 steel have been investigated using phenomenological constitutive model in the temperature range 300–873 K for the strain rates ranging from 3.16 × 10?5 to 1.26 × 10?3 s?1. The analysis indicated that the hybrid model reduced to Estrin–Mecking (E–M) one-internal-variable model at intermediate and high temperatures. Further, the analysis also indicated that dislocation dense martensite lath/cell boundaries and precipitates together act as effective barriers to dislocation glide in P92 steel. The flow behaviour of the steel was adequately described by the E–M approach for the range of temperatures and strain rates examined. Three distinct temperature regimes have been obtained for the variations in work-hardening parameters with respect to temperature and strain rate. Signatures of dynamic strain ageing in terms of the anomalous variations in work-hardening parameters at intermediate temperatures and the dominance of dynamic recovery at high temperatures have been observed. The evaluation of activation energy suggested that deformation is controlled by the dominance of cross-slip of dislocations at room and intermediate temperatures, and climb of dislocations at high temperatures. 相似文献
129.
130.
空间填充设计在计算机试验中应用十分广泛,当拟合回归模型时,正交的空间填充设计保证了因子效应估计的独立性.基于广义正交设计,文章给出了构造二阶正交拉丁超立方体设计和列正交设计的方法,新构造的设计不仅满足任意两列之间相互正交,还能保证每一列与任一列元素平方组成的列以及任两列元素相乘组成的列都正交.当某些正交的空间填充设计不存在时,具有较小相关系数的近似正交设计可作为替代设计使用.设计构造的灵活性为计算机试验在实践中的广泛应用提供了必要的支持. 相似文献