全文获取类型
收费全文 | 402篇 |
免费 | 29篇 |
国内免费 | 35篇 |
专业分类
化学 | 192篇 |
晶体学 | 2篇 |
力学 | 49篇 |
综合类 | 4篇 |
数学 | 22篇 |
物理学 | 56篇 |
无线电 | 141篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 18篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 14篇 |
2014年 | 19篇 |
2013年 | 15篇 |
2012年 | 13篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 20篇 |
2008年 | 23篇 |
2007年 | 16篇 |
2006年 | 22篇 |
2005年 | 28篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 13篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 18篇 |
1998年 | 19篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 2篇 |
1993年 | 18篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有466条查询结果,搜索用时 31 毫秒
151.
152.
Synthesis of a Two‐Dimensional Covalent Organic Monolayer through Dynamic Imine Chemistry at the Air/Water Interface
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wenyang Dai Feng Shao Jacek Szczerbiński Ryan McCaffrey Prof. Dr. Renato Zenobi Dr. Yinghua Jin Prof. Dr. A. Dieter Schlüter Prof. Dr. Wei Zhang 《Angewandte Chemie (International ed. in English)》2016,55(1):213-217
A two‐dimensional covalent organic monolayer was synthesized from simple aromatic triamine and dialdehyde building blocks by dynamic imine chemistry at the air/water interface (Langmuir–Blodgett method). The obtained monolayer was characterized by optical microscopy, scanning electron microscopy, and atomic force microscopy, which unambiguously confirmed the formation of a large (millimeter range), unimolecularly thin aromatic polyimine sheet. The imine‐linked chemical structure of the obtained monolayer was characterized by tip‐enhanced Raman spectroscopy, and the peak assignment was supported by spectra simulated by density functional theory. Given the modular nature and broad substrate scope of imine formation, the work reported herein opens up many new possibilities for the synthesis of customizable 2D polymers and systematic studies of their structure–property relationships. 相似文献
153.
In many industrial domains, there is a significant interest in obtaining temporal relationships among multiple variables in time-series data, given that such relationships play an auxiliary role in decision making. However, when transactions occur frequently only for a period of time, it is difficult for a traditional time-series association rules mining algorithm (TSARM) to identify this kind of relationship. In this paper, we propose a new TSARM framework and a novel algorithm named TSARM-UDP. A TSARM mining framework is used to mine time-series association rules (TSARs) and an up-to-date pattern (UDP) is applied to discover rare patterns that only appear in a period of time. Based on the up-to-date pattern mining, the proposed TSAR-UDP method could extract temporal relationship rules with better generality. The rules can be widely used in the process industry, the stock market, etc. Experiments are then performed on the public stock data and real blast furnace data to verify the effectiveness of the proposed algorithm. We compare our algorithm with three state-of-the-art algorithms, and the experimental results show that our algorithm can provide greater efficiency and interpretability in TSARs and that it has good prospects. 相似文献
154.
Yinghua Yu Liyao Ma Jiajin Xia Luoting Xin Lei Zhu Prof. Dr. Xueliang Huang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18418-18423
Tricyclic ring systems possessing a dibenzo structure joined to a seven-membered heterocyclic ring frequently show important biological activities. However, a modular approach to these molecules based on efficient intermolecular reaction of readily available chemicals is lacking. Herein, an unprecedented palladium-catalyzed formal [4+3] annulation for modular construction of these tricyclic systems is described. This reaction features easily accessible reactants (o-haloarylaldehydes and N-tosylhydrazones), broad substrate scope, and excellent functional group compatibility. The synthetic potential is demonstrated by the easy scale-up reactions, late-stage modification of complex molecules, and collective synthesis of bioactive molecules and approved drugs. 相似文献
155.
Dr. Lei Zhang Dr. Yinghua Jin Prof. Guo-Hong Tao Yu Gong Yiming Hu Prof. Ling He Prof. Wei Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21032-21037
A novel low-symmetry organic molecular cage with distinctive geometry was successfully synthesized from 5,5′-(propane-2,2-diyl)bis(2-hydroxyisophthalaldehyde) and 1,2-cyclohexanediamine building blocks, through the desymmetrized vertex design strategy. Single-crystal X-ray crystallographic analysis shows that the cage contains asymmetrical and nonplanar windows, exhibiting an unprecedented C2 symmetry and an efficient packing. The molecular cage structure was also characterized by FTIR, NMR, and MALDI-TOF. Quantum chemistry studies show that the cage structure contains rare intramolecular hydrogen-hydrogen (C−H⋅⋅⋅H−C) bonding interactions. The cage crystals exhibit high iodine vapor uptake (3.78 g g−1), which is among the highest for porous molecular materials. The knowledge gained in this study would open new possibilities for the design and synthesis of molecular cages with novel topologies targeting a broad range of applications. 相似文献
156.
157.
Nucleic acids can greatly enhance fluorescence intensity of the kaempferol (Km)-Al(III) system in the presence of silver nanoparticles (AgNPs). Based on this, a novel method for the determination of nucleic acids is proposed. Under studied conditions, there are linear relationships between the extent of fluorescence enhancement and the concentration of nucleic acids in the range of 5.0 × 10−9 to 2.0 × 10−6 g mL−1 for fish sperm DNA (fsDNA), 7.0 × 10−9 to 2.0 × 10−6 g mL−1 for salmon sperm DNA (smDNA) and 2.0 × 10−8 to 3.0 × 10−6 g mL−1 for yeast RNA (yRNA), and their detection limits are 2.5 × 10−9 g mL−1, 3.2 × 10−9 g mL−1 and 7.3 × 10−9 g mL−1, respectively. Samples were satisfactorily determined. And the system of Km-Al(III)-AgNPs was used as a fluorescence staining reagent for sensitive DNA detection by DNA pattern of agarose gel electrophoresis analysis. The results indicate that the fluorescence enhancement should be attributed to the formation of Km-Al(III)-AgNPs-nucleic acids aggregations through electrostatic attraction and adsorption bridging action of Al(III) and the surface-enhanced fluorescence effect of AgNPs. 相似文献
158.
激光重熔对TC4钛合金表面激光原位熔覆层微观组织与性能的影响 总被引:1,自引:1,他引:0
为了进一步提高激光原位熔覆层的质量,利用激光重熔方法对TC4钛合金表面激光原位熔覆层进行了处理。采用扫描电镜(SEM)、X射线衍射仪(XRD)和显微硬度计分别对比研究了熔层的显微组织、相分布和显微硬度。结果表明,适当工艺参数的激光重熔处理可以消除位于原位熔覆层底部的大气孔,可以使熔层中的陶瓷相分布更均匀,从而提高熔层的组织致密性;激光重熔处理后熔层硬度值的梯度变化减弱,熔层的平均显微硬度与质量的稳定性均得到提高。 相似文献
159.
In this paper, we investigate a coupled compressible Navier–Stokes/Allen–Cahn system which describes the motion of a mixture of two viscous compressible fluids. We prove the existence and uniqueness of global classical solution, the existence of weak solutions and the existence of unique strong solution of the Navier–Stokes/Allen–Cahn system in 1D for initial data ρ 0 without vacuum states. 相似文献
160.
为了克服CRR模型收敛的波动性,以及强调历史信息的预测作用的情况,提出了一个新奇的光滑收敛的树图模型.新模型基于历史信息,运用最小叉熵原理
来推导树图的关键参数p,u,d, 然后使用倒推法推断期权的价格.显然,新模型所得的期权的价格隐含着历史信息.由于最小叉熵原理是一个凸规划问题,能求得唯一的最优解,所以,新模型也适用于不完全金融市场期权定价.最后,数值算例表明,相比于CRR模型,新模型收敛光滑平稳且有更高的计算精度;对上涨(下跌)的二元期权、欧式期权,新模型都能光滑收敛于B-S公式. 相似文献