全文获取类型
收费全文 | 11954篇 |
免费 | 308篇 |
国内免费 | 86篇 |
专业分类
化学 | 1072篇 |
晶体学 | 63篇 |
力学 | 5347篇 |
综合类 | 6篇 |
数学 | 2819篇 |
物理学 | 3041篇 |
出版年
2023年 | 146篇 |
2022年 | 148篇 |
2021年 | 200篇 |
2020年 | 469篇 |
2019年 | 222篇 |
2018年 | 346篇 |
2017年 | 644篇 |
2016年 | 574篇 |
2015年 | 668篇 |
2014年 | 723篇 |
2013年 | 757篇 |
2012年 | 655篇 |
2011年 | 452篇 |
2010年 | 538篇 |
2009年 | 502篇 |
2008年 | 418篇 |
2007年 | 459篇 |
2006年 | 516篇 |
2005年 | 380篇 |
2004年 | 255篇 |
2003年 | 377篇 |
2002年 | 315篇 |
2001年 | 348篇 |
2000年 | 190篇 |
1999年 | 346篇 |
1998年 | 175篇 |
1997年 | 138篇 |
1996年 | 101篇 |
1995年 | 86篇 |
1994年 | 74篇 |
1993年 | 54篇 |
1992年 | 43篇 |
1991年 | 45篇 |
1990年 | 36篇 |
1989年 | 42篇 |
1988年 | 118篇 |
1987年 | 241篇 |
1986年 | 125篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1983年 | 49篇 |
1982年 | 27篇 |
1981年 | 19篇 |
1980年 | 29篇 |
1979年 | 15篇 |
1978年 | 20篇 |
1976年 | 18篇 |
1975年 | 37篇 |
1974年 | 39篇 |
1971年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Acta Mechanica Sinica - 相似文献
2.
3.
4.
Considering the random impulses of mechanical noise and the limitations involved while identifying mechanical fault impulse signals via traditional measurement indices of signal-to-noise ratio, which require the characteristic frequency to be known in advance, this study proposes an adaptive unsaturated stochastic resonance method employing maximum cross-correlated kurtosis as the signal detection index. The proposed method combines the features of a cross-correlated coefficient to indicate periodic fault transients and those of spectrum kurtosis to locate these transients in the frequency domain. Actual vibration signals collected from motor and gear bearings subjected to heavy noise are used to demonstrate the effectiveness of the proposed method. Through a coarse tree-based machine learning method, the proposed method is verified to be more suitable for explaining the periodic impulse components of bearing signals, as compared to the ensemble empirical mode decomposition denoising method and unsaturated stochastic resonance using the kurtosis-intercorrelation index. 相似文献
5.
Liu Jingze Fei Qingguo Wu Shaoqing Tang Zhenhuan Zhang Dahai 《Nonlinear dynamics》2021,106(3):1869-1890
Nonlinear Dynamics - Rolling bearing and squeeze film damper will introduce structural nonlinearity into the dynamic model of aeroengine. Rubbing will occur due to the clearance reduction design of... 相似文献
6.
Bingjie Chen Dr. Lianhai Zu Dr. Yao Liu Dr. Ruijing Meng Yutong Feng Prof. Chengxin Peng Feng Zhu Tianzi Hao Jiajia Ru Prof. Yonggang Wang Prof. Jinhu Yang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(8):3161-3166
Incorporating nanoscale Si into a carbon matrix with high dispersity is desirable for the preparation of lithium-ion batteries (LIBs) but remains challenging. A space-confined catalytic strategy is proposed for direct superassembly of Si nanodots within a carbon (Si NDs⊂C) framework by copyrolysis of triphenyltin hydride (TPT) and diphenylsilane (DPS), where Sn atomic clusters created from TPT pyrolysis serve as the catalyst for DPS pyrolysis and Si catalytic growth. The use of Sn atomic cluster catalysts alters the reaction pathway to avoid SiC generation and enable formation of Si NDs with reduced dimensions. A typical Si NDs⊂C framework demonstrates a remarkable comprehensive performance comparable to other Si-based high-performance half LIBs, and higher energy densities compared to commercial full LIBs, as a consequence of the high dispersity of Si NDs with low lithiation stress. Supported by mechanic simulations, this study paves the way for construction of Si/C composites suitable for applications in future energy technologies. 相似文献
7.
The accumulation of material degradation under contact with aggressive aqueous environments could lead to reduced structural reliability. In terms of hydrated cementitious materials, such interactions often result in the chemo-physical-mechanical (CPM) degradation, which represents a multiphysics process of high non-linearity and complexity. By further considering the inevitable uncertainties associated with both the materials and the serving conditions, solving such a process requires novel probabilistic approaches. This paper presents a stochastic chemo-physical-mechanical (SCPM) degradation analysis on the hydrated cement under acidic environment. The SCPM analysis consists of modelling the stochastic chemophysical degradation by finite element method, and assessing the mechanical deterioration through analytical micromechanics. The proposed modelling framework couples the conventional Monte Carlo Simulation with a novel support vector regression algorithm. The present method is able to not only address the detailed degradation mechanisms, but also ensure low computational costs for an accurate SCPM degradation assessment. 相似文献
8.
《Wave Motion》2018
The evolution of surface gravity waves is driven by nonlinear interactions that trigger an energy cascade similarly to the one observed in hydrodynamic turbulence. This process, known as wave turbulence, has been found to display anomalous scaling with deviation from classical turbulent predictions due to the emergence of coherent and intermittent structures on the water surface. In the ocean, waves are spread over a wide range of directions, with a consequent attenuation of the nonlinear properties. A laboratory experiment in a large wave facility is presented to discuss the sensitivity of wave turbulence on the directional properties of model wave spectra. Results show that the occurrence of coherent and intermittent structures become less likely with the broadening of the wave directional spreading. There is no evidence, however, that intermittency completely vanishes. 相似文献
9.
10.