全文获取类型
收费全文 | 127篇 |
免费 | 12篇 |
国内免费 | 10篇 |
专业分类
化学 | 79篇 |
力学 | 43篇 |
数学 | 2篇 |
物理学 | 25篇 |
出版年
2024年 | 4篇 |
2023年 | 16篇 |
2022年 | 19篇 |
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 16篇 |
2018年 | 2篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 1篇 |
2012年 | 6篇 |
2011年 | 2篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1991年 | 3篇 |
排序方式: 共有149条查询结果,搜索用时 15 毫秒
41.
42.
Jiahao Jiao Wenqi Jin Prof. Min Zhang Zhiyong Guo Prof. Zhihua Yang Prof. Shilie Pan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(4):e202103966
Two new sodium aluminum borates, Na3AlB8O15 and Na3Al2B7O15, have been successfully synthesized by the high-temperature solution method. They crystallize in the different space groups, P21/c and P2/c, respectively. The B−O configurations of β-Na2B6O10, Na3AlB8O15 and Na3Al2B7O15 are compared to feature complicated different dimensional open-framework structures caused by the substitution of [BO4] by [AlO4] covalent tetrahedra. Moreover, the experimental results indicate that Na3AlB8O15 and Na3Al2B7O15 have short ultraviolet (UV) cutoff edges (<187 nm). The first-principles calculations show that Na3AlB8O15 and Na3Al2B7O15 have moderate birefringence (0.075 and 0.041@1064 nm, respectively). 相似文献
43.
Xu Guiqing Wang Jiahao Zhou Yingjie Mao Longfei 《Russian Journal of Organic Chemistry》2020,56(10):1775-1778
Russian Journal of Organic Chemistry - cis-8-Methoxy-1,3-diazaspiro[4.5]decane-2,4-dione, the key intermediate in the synthesis of spirotetramat, was synthesized by catalytic hydrogenation,... 相似文献
44.
基于EGS5与PARMELA模拟软件组成的高能电子成像系统,对暗场成像的模拟研究发现,通过调节光阑位置实现的暗场成像结果存在失真现象。针对该失真现象提出的改进方案,消除了暗场成像结果的失真。通过对40 MeV电子透射7~224 μm的铝样品开展的成像模拟结果表明:40 MeV高能电子暗场成像技术在铝样品厚度小于25 μm情况下具有明显的面密度分辨优势,且空间分辨率达到μm量级,非常适用于高能量密度物质诊断。 相似文献
45.
Electronic tuning by para substitutions was explored to achieve a highly active manganese N-heterocyclic carbene pincer complex for the selective electrocatalytic reduction of CO2 to CO. [MnCNCOMe]BF4(L2-Mn) bearing an electron-donating group(–OMe) showed high activity with 63 × catalytic current enhancement, average Faradaic efficiency of 104%, and a TOFmax value of 26,127 s-1, which is 127 times higher than that of unsubstituted [MnCNC 相似文献
46.
基于首超破坏机制的大跨斜拉桥抖振动力可靠性分析 总被引:2,自引:0,他引:2
分别采用泊松分布和马尔可夫过程,给出了在一次强风作用下以及在设计基准期内桥梁结构某一特定截面或节点的抖振动力可靠性分析方法。然后,考虑斜拉桥的结构特点及其承受风荷栽的具体情况,确定了以斜拉桥的主梁系统为研究对象的结构体系抖振动力可靠性分析模型。在此基础上,采用串联失效模式,建立了斜拉桥主梁系统抖振动力可靠性分析过程。本文采用有限元法分析结构的空气静力响应。为了快速、准确地计算结构的抖振响应,考虑气弹力与抖振力的联合作用以及多模态耦合效应,采用有限元法和虚拟激励法相结合分析结构的抖振响应。最后,以某大跨斜拉桥为工程背景,对其主梁系统进行了基于刚度要求的抖振动力可靠性分析。 相似文献
47.
48.
Jiaying Li Han Liu Jiaxun Liang Jiahao Dong Bin Pang Ziyang Hao Xin Zhao 《Entropy (Basel, Switzerland)》2022,24(8)
Multipoint Optimal Minimum Entropy Deconvolution Adjusted (MOMEDA) is an advanced deconvolution method, which can effectively inhibit the interference of background noise and distinguish the fault period by calculating the multipoint kurtosis values. However, multipoint kurtosis (MKurt) could lead to misjudgment since it is sensitive to spurious noise spikes. Considering that L-kurtosis has good robustness with noise, this paper proposes a multipoint envelope L-kurtosis (MELkurt) method for establishing the temporal features. Then, an enhanced image representation method of vibration signals is proposed by employing the Gramian Angular Difference Field (GADF) method to convert the MELkurt series into images. Furthermore, to effectively learn and extract the features of GADF images, this paper develops a deep learning method named Conditional Super Token Transformer (CSTT) by incorporating the Super Token Transformer block, Super Token Mixer module, and Conditional Positional Encoding mechanism into Vision Transformer appropriately. Transfer learning is introduced to enhance the diagnostic accuracy and generalization capability of the designed CSTT. Consequently, a novel bearing fault diagnosis framework is established based on the presented enhanced image representation and CSTT. The proposed method is compared with Vision Transformer and some CNN-based models to verify the recognition effect by two experimental datasets. The results show that MELkurt significantly improves the fault feature enhancement ability with superior noise robustness to kurtosis, and the proposed CSTT achieves the highest diagnostic accuracy and stability. 相似文献
49.
Determination of the half-life of 184gRe and the isomeric ratio of 184m,gRe induced by D-T neutrons 下载免费PDF全文
Changlin Lan Yuting Wei Jiahao Wang Xianlin Yang Gong Jiang Yujie Ge Chao Xu Li Feng Xiaojun Li 《中国物理C(英文版)》2022,46(11):114001-114001-9
The isomeric ratio of 184m, gRe and the half-life of 184gRe were measured in the 185Re (n, 2n) 184Re reaction at 14.8 MeV, and the uncertainty was discussed in detail. The measurements were performed using the activation method implemented for a rhenium sample using the K-400 neutron generator at the Chinese Academy of Engineering Physics (CAEP). Isomeric state and ground state nuclei of 184Re were identified by their γ-ray spectra. To eliminate the effect of the γ-ray emitted from the isomer on the counting of the ground state characteristic peaks, the isomeric ratio of 184m, gRe was calculated to be 0.29 ± 0.11 according to the neutron activation cross-section formula. This result is consistent with previous data within the uncertainty and can be used to determine parameters that characterize the dependence of the level density on the excitation energy and angular momentum. Through exponential function fitting and a detailed discussion of the uncertainty evaluation, the half-life of 184gRe was determined as 35.43 ± 0.16 d, which is consistent with the currently recommended value; however, the uncertainty assessment of the latter was barely documented. In addition, this study indicates that the half-life of the ground state can be obtained by eliminating the contamination of γ-rays emitted from the isomer, which provides the possibility of determining the half-lives of nuclides containing isomers. 相似文献
50.
Quantum adiabatic evolution describes the dynamical evolution of a slowly driven Hamiltonian. In most systems undergoing spontaneous symmetry-breaking transitions, the symmetry-protected quantum adiabatic evolution can still appear, even when the two lowest eigenstates become degenerate. Here, a general derivation to revisit the symmetry-dependent transition and the symmetry-dependent adiabatic condition (SDAC) is given. Further, based on the SDAC, an adiabatic-parameter-fixed sweeping scheme is used for achieving fast adiabatic evolution, which is more efficient than the linear sweeping scheme. In the limit of small adiabatic parameter, an analytic inequality is obtained for the ground state fidelity only dependent on the adiabatic parameter. The general statements are then demonstrated via two typical systems. Besides, the robustness of the symmetry-dependent adiabatic evolution against weak symmetry-breaking sources is studied. The findings can be tested via the techniques in quantum annealing and may provide promising applications in practical quantum technologies. 相似文献