全文获取类型
收费全文 | 283篇 |
免费 | 32篇 |
国内免费 | 31篇 |
专业分类
化学 | 111篇 |
晶体学 | 5篇 |
力学 | 64篇 |
综合类 | 1篇 |
数学 | 52篇 |
物理学 | 113篇 |
出版年
2025年 | 3篇 |
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 25篇 |
2021年 | 16篇 |
2020年 | 29篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 13篇 |
2015年 | 17篇 |
2014年 | 27篇 |
2013年 | 12篇 |
2012年 | 21篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 11篇 |
2008年 | 3篇 |
2007年 | 8篇 |
2006年 | 2篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2002年 | 2篇 |
2001年 | 3篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1968年 | 1篇 |
1967年 | 4篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1960年 | 2篇 |
1952年 | 2篇 |
排序方式: 共有346条查询结果,搜索用时 15 毫秒
1.
Most existing beam formulations assume that the cross section of the beam remains rigid regardless of the amplitude of the displacement. The absolute nodal coordinate formulation (ANCF); however, allows for the deformation of the cross section and leads to a more general beam models that capture the coupling between different modes of displacement. This paper examines the effect of the order of interpolation on the modes of deformation of the beam cross section using ANCF finite elements. To this end, a new two-dimensional shear deformable ANCF beam element is developed. The new finite element employs a higher order of interpolation, and allows for new cross section deformation modes that cannot be captured using previously developed shear deformable ANCF beam elements. The element developed in this study relaxes the assumption of planar cross section; thereby allowing for including the effect of warping as well as for different stretch values at different points on the element cross section. The displacement field of the new element is assumed to be cubic in the axial direction and quadratic in the transverse direction. Using this displacement field, more expressions for the element extension, shear and the cross section stretch can be systematically defined. The change in the cross section area is measured using Nanson’s formula. Measures of the shear angle, extension, and cross section stretch can also be systematically defined using coordinate systems defined at the element material points. Using these local coordinate systems, expressions for a nominal shear angle are obtained. The differences between the cross section deformation modes obtained using the new higher order element and those obtained using the previously developed lower order elements are highlighted. Numerical examples are presented in order to compare the results obtained using the new finite element and the results obtained using previously developed ANCF finite elements. 相似文献
2.
《中国化学快报》2020,31(10):2698-2704
Multiple pollutants including pathogenic microorganism contaminations and emerging organic contaminations (EOCs) have shown a growing threat to the environment, especially the natural waters. However, the control and removal of pathogenic microorganism contaminations and EOCs have been greatly limited since limited knowledge of their environmental behaviors. Thus, a novel and efficient photocatalyst Ag2O/BiOBr heterojunction was synthesized and used for removal of multiple pollutants including Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), tetracycline and acetaminophen under visible light. The results showed that there were valid electron transfer pathways between BiOBr and Ag2O, the main electron transfer direction was the BiOBr to Ag2O. Photo-generated electrons were stored in Ag2O and thus separation efficiency between holes and photo-generated electrons was obviously enhanced. Active oxygen species were highly produced and eventually end up with the high efficiency of removal of multiple pollutants. For Ag2O/BiOBr with Ag2O content at 3% (the best performance) under visible light, log decrease of E. coli was 7.16 (removal efficiency was 100%) in 120 min, log decrease of S. aureus was 7.23 (removal efficiency was 100%) in 160 min, C/C0 of tetracycline was 0.06 in 180 min, C/C0 of acetaminophen was 0.17 in 180 min. This work could provide a promising candidate in the actual contaminated natural waters for cleaning multiple pollutants. 相似文献
3.
4.
Photoluminescence study of AlGaInP/GaInP quantum well intermixing induced by zinc impurity diffusion
《Journal of Crystal Growth》2007,298(2):140-144
AlGaInP/GaInP quantum well intermixing phenomena induced by Zn impurity diffusion at 540 °C were studied using room-temperature photoluminescence (PL) spectroscopy. As the diffusion time increased from 40 to 120 min, PL blue shift taken on the AlGaInP/GaInP quantum well regions increased from 36.3 to 171.6 meV. Moreover, when the diffusion time was equal to or above 60 min, it was observed firstly that a PL red shift occurred with a PL blue shift on the samples. After detailed analysis, it was found that the red-shift PL spectra were measured on the Ga0.51In0.49P buffer layer of the samples, and the mechanism of the PL red shift and the PL blue shift were studied qualitatively. 相似文献
5.
Li Limin Zhao Gaoyang Lei Li Li Chengshan 《Journal of Sol-Gel Science and Technology》2021,100(3):414-422
Journal of Sol-Gel Science and Technology - Herein, the chelated precursor solution (Mg/BzAc) was synthesized using magnesium acetate as raw material and benzoylacetone as chemical modifier. The... 相似文献
6.
《Communications in Nonlinear Science & Numerical Simulation》2014,19(7):2294-2308
This paper presents an explicit, computationally efficient, recursive formula for computing the normal forms, center manifolds and nonlinear transformations for general n-dimensional systems, associated with semisimple singularities. Based on the formula, we develop a Maple program, which is very convenient for an end-user who only needs to prepare an input file and then execute the program to “automatically” generate the result. Several examples are presented to demonstrate the computational efficiency of the algorithm. 相似文献
7.
Rechargeable metal-ion batteries (RMIBs), as one of the most viable technologies for electric vehicles (EVs) and large-scale energy storage (EES), have received extensive research attention for a long time. Electrode materials play a decisive role on capacity, energy, and power density, which directly affect the practical applications of RMIBs in EVs and EES. As an electrode material, layered metallic vanadium disulfide (VS2) has theoretically and experimentally produced inspiring results because of its synthetic characteristics of continuously adjustable V valence, large interlayer spacing, weak interlayer interactions, and high surface activity. Herein, the synthetic strategies, theoretical metal-ion storage sites, diffusion kinetics, and experimental electrochemical reaction mechanisms of VS2 for RMIBs are systematically introduced. Emphatically, the critical issues that affect the metal-ion storage properties of the VS2 electrode and three major enhancement strategies, namely, optimizing the electrolyte and cutoff voltage, constructing a space-confined structure, and controlling the crystal structure are summarized, with the aim of promoting the development of transition-metal dichalcogenides. Finally, the challenges and opportunities for the future development of VS2 in the energy-storage field are presented. It is hoped that this review can attract attention from researchers for investigations into emerging layered metallic VS2 and provide insights toward the design of an excellent VS2 electrode material for next-generation, high-performance RMIBs. 相似文献
8.
Ke Xu Dr. Liang Kou Cheng Zhang Chao Zhang Jing Sun Zhanyuan Tian Dr. Jing Zhang Prof. Caiyin You 《ChemElectroChem》2020,7(23):4730-4736
The nickel-rich LiNi0.91Co0.06Al0.03O2 cathode material has attracted wide attention due to its high energy density and appropriate thermal stability; however, its practical application has been greatly restricted by exorbitant residual LiOH/Li2CO3 and poor cycling performance. In this work, we have reduced the residual LiOH/Li2CO3 by washing the LiNi0.91Co0.06Al0.03O2 fabricated through a high-temperature solid-state method and improved the cycling performance with a composite coating process. The results show that the amount of residual LiOH/Li2CO3 in the washed materials is significantly decreased, which is very favorable for the processability of materials. LiNi0.91Co0.06Al0.03O2 with 0.1 wt% composite coating exhibits optimum properties: the discharge capacity reaches 217.4 mAh/g at 0.1 C, the cycling retention still remains at 93.7 % after 100 cycles at 1 C, and the cycling retention of the soft-packing battery remains as high as 81.7 % after 800 cycles at 1 C. The excellent electrochemical performances are attributed to the synergistic effect of excellent fluidity of H3BO3 and outstanding stability of Y2O3, mitigating the interface reaction between electrolyte and cathode material. 相似文献
9.
Ship-radiated noise is one of the important signal types under the complex ocean background, which can well reflect physical properties of ships. As one of the valid measures to characterize the complexity of ship-radiated noise, permutation entropy (PE) has the advantages of high efficiency and simple calculation. However, PE has the problems of missing amplitude information and single scale. To address the two drawbacks, refined composite multi-scale reverse weighted PE (RCMRWPE), as a novel measurement technology of describing the signal complexity, is put forward based on refined composite multi-scale processing (RCMP) and reverse weighted PE (RWPE). RCMP is an improved method of coarse-graining, which not only solves the problem of single scale, but also improves the stability of traditional coarse-graining; RWPE has been proposed more recently, and has better inter-class separability and robustness performance to noise than PE, weighted PE (WPE), and reverse PE (RPE). Additionally, a feature extraction scheme of ship-radiated noise is proposed based on RCMRWPE, furthermore, RCMRWPE is combined with discriminant analysis classifier (DAC) to form a new classification method. After that, a large number of comparative experiments of feature extraction schemes and classification methods with two artificial random signals and six ship-radiated noise are carried out, which show that the proposed feature extraction scheme has better performance in distinguishing ability and stability than the other three similar feature extraction schemes based on multi-scale PE (MPE), multi-scale WPE (MWPE), and multi-scale RPE (MRPE), and the proposed classification method also has the highest recognition rate. 相似文献
10.
A major advantage of the use of passive sonar in the tracking multiple underwater targets is that they can be kept covert, which reduces the risk of being attacked. However, the nonlinearity of the passive Doppler and bearing measurements, the range unobservability problem, and the complexity of data association between measurements and targets make the problem of underwater passive multiple target tracking challenging. To deal with these problems, the cardinalized probability hypothesis density (CPHD) recursion, which is based on Bayesian information theory, is developed to handle the data association uncertainty, and to acquire existing targets’ numbers and states (e.g., position and velocity). The key idea of the CPHD recursion is to simultaneously estimate the targets’ intensity and the probability distribution of the number of targets. The CPHD recursion is the first moment approximation of the Bayesian multiple targets filter, which avoids the data association procedure between the targets and measurements including clutter. The Bayesian-filter-based extended Kalman filter (EKF) is applied to deal with the nonlinear bearing and Doppler measurements. The experimental results show that the EKF-based CPHD recursion works well in the underwater passive multiple target tracking system in cluttered and noisy environments. 相似文献