全文获取类型
收费全文 | 396067篇 |
免费 | 20678篇 |
国内免费 | 14748篇 |
专业分类
化学 | 219053篇 |
晶体学 | 4797篇 |
力学 | 14218篇 |
综合类 | 783篇 |
数学 | 75672篇 |
物理学 | 116970篇 |
出版年
2023年 | 4491篇 |
2022年 | 6538篇 |
2021年 | 9905篇 |
2020年 | 10192篇 |
2019年 | 8603篇 |
2018年 | 12027篇 |
2017年 | 12281篇 |
2016年 | 10474篇 |
2015年 | 11625篇 |
2014年 | 16906篇 |
2013年 | 25715篇 |
2012年 | 22262篇 |
2011年 | 23209篇 |
2010年 | 19189篇 |
2009年 | 19343篇 |
2008年 | 19873篇 |
2007年 | 20708篇 |
2006年 | 18715篇 |
2005年 | 14619篇 |
2004年 | 12570篇 |
2003年 | 11254篇 |
2002年 | 10298篇 |
2001年 | 10369篇 |
2000年 | 7650篇 |
1999年 | 6995篇 |
1998年 | 5551篇 |
1997年 | 4765篇 |
1996年 | 4022篇 |
1995年 | 3111篇 |
1994年 | 2733篇 |
1993年 | 2699篇 |
1992年 | 2477篇 |
1991年 | 3090篇 |
1990年 | 3123篇 |
1989年 | 2825篇 |
1988年 | 4001篇 |
1987年 | 2331篇 |
1986年 | 2097篇 |
1985年 | 2896篇 |
1984年 | 2915篇 |
1983年 | 2247篇 |
1982年 | 2604篇 |
1981年 | 2372篇 |
1980年 | 2037篇 |
1979年 | 2175篇 |
1978年 | 2349篇 |
1977年 | 2084篇 |
1976年 | 2078篇 |
1975年 | 2003篇 |
1973年 | 2049篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
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
45.
Karandashev S. A. Lukhmyrina T. S. Matveev B. A. Remennyi M. A. Usikova A. A. 《Optics and Spectroscopy》2021,129(11):1231-1235
Optics and Spectroscopy - The current–voltage characteristics and photocurrent of “monolithic” diode optical pairs optically coupled by a substrate made of InAs common for them... 相似文献
46.
Laser cooling of a molecule with heavy nuclei is often complicated because of the density distribution of the electronic states. Here, we evaluate the feasibility of the laser cooling of the SrI molecule by calculating the potential energy curves and transition dipole moments of the ground and low-lying excited states using the multi-reference configuration interaction plus Davidson corrections (MRCI + Q) and the all-electron basis sets of ANO-RCC. The relativistic effect and the spin-orbit coupling splits are included, because both Sr and I are heavy atoms. Based on the obtained potential energy curves, we solve the Schrödinger equation of nuclear motion to determine the rovibrational energy levels and the Franck-Condon factors. The spectroscopic parameters are obtained by fitting the rovibrational energy levels with the Dunham expression. The radiation lifetimes, the Doppler and recoil temperatures between the X2Σ+ and the 2Π1/2/2Π3/2/B2Σ+ states are calculated. 5-color laser cooling schemes for the molecule are proposed, which can lead to the total effective Franck-Condon factors being 0.99983, 0.99979, and 0.99941 for the three transitions, respectively. All the obtained results suggest that the SrI molecule is a feasible candidate for laser cooling. 相似文献
47.
48.
Optics and Spectroscopy - Optical investigations of crystals of solid solutions NdxGd1 – xCr3(BO3)4, 0.01 ≤ x ≤ 1, have been performed. Absorption spectra in the... 相似文献
49.
Technical Physics - Taking damping into account in the problems of structural dynamics is an important and nontrivial problem. Its complexity is primarily determined by the required specification... 相似文献
50.
Siberian Mathematical Journal - Suppose that $ n $ is an integer, $ n\geq 3 $ . We prove that a periodic group saturated with a set of the finite simple groups $ O_{2n+1}(q) $ , where $ q $ is... 相似文献