全文获取类型
收费全文 | 6479篇 |
免费 | 713篇 |
国内免费 | 606篇 |
专业分类
化学 | 1969篇 |
晶体学 | 3篇 |
力学 | 767篇 |
综合类 | 126篇 |
数学 | 2847篇 |
物理学 | 1252篇 |
无线电 | 834篇 |
出版年
2024年 | 16篇 |
2023年 | 46篇 |
2022年 | 113篇 |
2021年 | 121篇 |
2020年 | 158篇 |
2019年 | 145篇 |
2018年 | 150篇 |
2017年 | 208篇 |
2016年 | 207篇 |
2015年 | 190篇 |
2014年 | 321篇 |
2013年 | 413篇 |
2012年 | 329篇 |
2011年 | 356篇 |
2010年 | 313篇 |
2009年 | 376篇 |
2008年 | 402篇 |
2007年 | 418篇 |
2006年 | 347篇 |
2005年 | 327篇 |
2004年 | 316篇 |
2003年 | 313篇 |
2002年 | 269篇 |
2001年 | 229篇 |
2000年 | 224篇 |
1999年 | 199篇 |
1998年 | 182篇 |
1997年 | 175篇 |
1996年 | 156篇 |
1995年 | 129篇 |
1994年 | 88篇 |
1993年 | 72篇 |
1992年 | 101篇 |
1991年 | 73篇 |
1990年 | 51篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 29篇 |
1986年 | 25篇 |
1985年 | 31篇 |
1984年 | 18篇 |
1983年 | 6篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1974年 | 3篇 |
排序方式: 共有7798条查询结果,搜索用时 18 毫秒
1.
It is known that under resonance conditions, a group of strongly interacting bosonic atoms, trapped in a double-well potential, mimics a single particle, performing Rabi oscillations between the wells. By implication, all atoms need to tunnel at roughly the same time, even though the Bose–Hubbard Hamiltonian accounts only for one-atom-at-a-time transfers. The mechanism of this collective behavior is analyzed, the Rabi frequencies in the process are evaluated, and the limitation of this simple picture is discussed. In particular, it is shown that the small rapid oscillations superimposed on the slow Rabi cycle result from splitting the transferred cluster at the sudden onset of tunnelling, and disappear if tunnelling is turned on gradually. 相似文献
2.
3.
Motor Imagery Electroencephalography (MI-EEG) has shown good prospects in neurorehabilitation, and the entropy-based nonlinear dynamic methods have been successfully applied to feature extraction of MI-EEG. Especially based on Multiscale Fuzzy Entropy (MFE), the fuzzy entropies of the τ coarse-grained sequences in τ scale are calculated and averaged to develop the Composite MFE (CMFE) with more feature information. However, the coarse-grained process fails to match the nonstationary characteristic of MI-EEG by a mean filtering algorithm. In this paper, CMFE is improved by assigning the different weight factors to the different sample points in the coarse-grained process, i.e., using the weighted mean filters instead of the original mean filters, which is conductive to signal filtering and feature extraction, and the resulting personalized Weighted CMFE (WCMFE) is more suitable to represent the nonstationary MI-EEG for different subjects. All the WCMFEs of multi-channel MI-EEG are fused in serial to construct the feature vector, which is evaluated by a back-propagation neural network. Based on a public dataset, extensive experiments are conducted, yielding a relatively higher classification accuracy by WCMFE, and the statistical significance is examined by two-sample t-test. The results suggest that WCMFE is superior to the other entropy-based and traditional feature extraction methods. 相似文献
4.
Several phenoxy-imine ligands bearing o-trityl group in phenoxy moiety RN=CHArOH (Ar = C6H2(CPh3)tBu, R = 2,6-Me2C6H3 ( L 1 H ); 2,6-iPr2C6H3 ( L 2 H ); 3,5-(CF3)2C6H3 ( L 3 H ); 3,5-(OMe)2C6H3 ( L 4 H ); CHPh2 ( L 5 H ); CPh3 ( L 6 H )) were synthesized and characterized by1H NMR and 13C NMR spectroscopy. The vanadium complexes based on these ligands LVCl2(THF)2 ( 1–6 ) were synthesized via conventional transmetalation reaction in moderate to high yields. Complexes 1–6 were fully characterized by FT-IR, elemental analyses and the molecular structures of 1 , 2 ·H2O, (2 ·H2O ) 2 (μ-Cl) 2 , 4 , and 5 were confirmed by X-ray crystallographic analysis in which the six-coordinated vanadium centers are in a typical octahedral geometry. Upon activation with Et2AlCl in toluene, complexes 1–6 showed high activities in ethylene polymerization affording polymers with moderate molecular weight (5.9–11.8 × 104 Da). Moreover, in hexane or CH2Cl2, 1–6 /Et2AlCl exhibited enhanced activities. When activated with MAO or MMAO in toluene, these complexes showed relatively low activities but afforded polymers with ultra-high molecular weight (up to 3.30 × 106 Da). 1–6 /Et2AlCl also showed high activities in ethylene/1-hexene copolymerization at room temperature giving moderate molecular-weight polymers (6.5–11.4 × 104 Da) with co-monomer incorporation being of 6.0 ~ 7.8%. 相似文献
5.
Zk线性码的对称形式的MacWilliams恒等式 总被引:8,自引:2,他引:6
该文定义了Zk线性码的码字的对称重量计数公式,利用离散的Hadamard变换,建立了线性码与其对偶码之间的对称形式的MacWilliams恒等式. 相似文献
6.
Boundedness of commutators on homogeneous Herz spaces 总被引:9,自引:0,他引:9
The boundedness on homogeneous Herz spaces is established for a large class of linear commutators generated by BMO(R
n
) functions and linear operators of rough kernels which include the Calderón-Zygmund operators and the Ricci-Stein oRfiUatory
singular integrals with rough kernels.
Project supponed in pan by the National h’atural Science Foundation of China (Grant No. 19131080) and the NEDF of China. 相似文献
7.
8.
本文给出了C^n中子空间之间最大和最小主角在矩阵逼近,投影算子的扰动分析,群逆以及Oraxin逆的扰动估计,条件数理论,Bott-Duffin系统扰动分析中一些应用。 相似文献
9.
利用射影几何方法在小缺陷码中,NMDS码是链条件码;给出k维NμMDS(0μk-2)码满足链条件的一个充要条件与一些易判断的充分条件. 相似文献
10.
Lin Surong 《Annals of Differential Equations》2006,22(4):517-523
The singularly perturbed boundary value problem for nonlinear higher order ordinary differential equation involving two small parameters has been considered. Under appropriate assumptions, for the three cases:ε/μ2→0(μ→0),μ2/ε→0 (ε→0) andε=μ2, the uniformly valid asymptotic solution is obtained by using the expansion method of two small parameters and the theory of differential inequality. 相似文献