全文获取类型
收费全文 | 4829篇 |
免费 | 144篇 |
国内免费 | 19篇 |
专业分类
化学 | 3461篇 |
晶体学 | 40篇 |
力学 | 113篇 |
数学 | 662篇 |
物理学 | 716篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 85篇 |
2021年 | 116篇 |
2020年 | 82篇 |
2019年 | 74篇 |
2018年 | 66篇 |
2017年 | 69篇 |
2016年 | 178篇 |
2015年 | 114篇 |
2014年 | 137篇 |
2013年 | 296篇 |
2012年 | 355篇 |
2011年 | 390篇 |
2010年 | 216篇 |
2009年 | 180篇 |
2008年 | 329篇 |
2007年 | 321篇 |
2006年 | 260篇 |
2005年 | 306篇 |
2004年 | 231篇 |
2003年 | 201篇 |
2002年 | 168篇 |
2001年 | 62篇 |
2000年 | 63篇 |
1999年 | 37篇 |
1998年 | 45篇 |
1997年 | 35篇 |
1996年 | 70篇 |
1995年 | 32篇 |
1994年 | 33篇 |
1993年 | 43篇 |
1992年 | 26篇 |
1991年 | 29篇 |
1990年 | 36篇 |
1989年 | 27篇 |
1988年 | 27篇 |
1987年 | 34篇 |
1986年 | 17篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1974年 | 6篇 |
1972年 | 3篇 |
排序方式: 共有4992条查询结果,搜索用时 15 毫秒
51.
Javier Gamboa Félix Javier Jiménez-Jiménez Alberto Nieto Ignacio Cobeta Alberto Vegas Miguel Ortí-Pareja Teresa Gasalla José Antonio Molina Esteban García-Albea 《Journal of voice》1998,12(4):444-452
To quantify several acoustic features of the voice in patients with essentialtremor (ET), 28 patients and 28 age- and sex-matched controls were studied. ET severity was assessed with the rating scale for tremor of Fahn, Tolosa, and Marín. The Computerized Speech Lab 4300 program (Kay Elemetrics) was used. Two-second samples of a sustained /a/ and a sentence were captured with a microphone and laryngograph equipment. Measures included fundamental frequency (F0), frequency perturbation (fitter, Koike algorithm), intensity perturbation (shimmer, Horii algorithm), and harmonic-to-noise ratio (H/N, Yumoto algorithm) of the vowel /a/, and the frequency and intensity variability of the sentence, phonational range, and dynamic range at the natural frequency, maximum phonational time, and s/z ratio. All subjects underwent indirect laryngoscopy and/or laryngeal fibroscopy. When compared with controls, ET patients showed higher jitter, lower H/N ratio (the last one only with laryngographic signal), of the vowel /a/, lower frequency variability in the microphonc signal, lower intensity variability in the laryngographic signal of the sentence, and significantly lower dynamic range at natural frequency of phonation. ET patients reported higher frequency of the presence of high voice intensity, tremor, and struggle. Several acoustic parameters were influenced by the severity of the disease, including shimmer, jitter, H/N ratio, frequency variability of the sentence, and s/z ratio, although neither of the acoustic analysis values or the phonetometric measurements were affected by the presence of voice tremor or by a successful pharmacological treatment of ET. 相似文献
52.
Miguel Navarro 《Foundations of Physics Letters》1998,11(6):585-593
Rules of quantization and equations of motion for a finite-dimensional formulation of quantum field theory are proposed which fulfill the following properties: (a) Both the rules of quantization and the equations of motion are covariant; (b) the equations of evolution are second order in derivatives and first order in derivatives of the spacetime coordinates; and (c) these rules of quantization and equations of motion lead to the usual (canonical) rules of quantization and the (Schrödinger) equation of motion of quantum mechanics in the particular case of mechanical systems. We also comment briefly on further steps to fully develop a satisfactory quantum field theory and the difficuties which may be encountered when doing so. 相似文献
53.
Russian Physics Journal - Aiming at problems of low probability of interception and poor anti-jamming performance of the multi-output radar, the numerical simulation based on a chaos optimization... 相似文献
54.
We claim that physics has been constructed because three “philosophical” principles have been respected, namely, realism,
locality, and consistency. These principles lead to an interpretation of quantum mechanics (QM) in terms of local hidden-variables
theories (LHV). In order to prove that LHV have not been refuted, we analyze the empirical proofs of Bell's inequalities and
we argue that none is loophole-free. Then we propose a restricted QM that does not contain measurement postulates and that
does not claim that all state vectors (self-adjoint operators) are states (observables). The contradiction of such restricted
QM with Bell's inequality cannot be shown as a theorem, but only by the design of a loophole-free experiment. Finally, we
argue that noise has been underestimated in quantum theory. It does not appear in QM, but it is essential in quantum field
theory. We conjecture that noise will prevent the violation of Bell's inequality. 相似文献
55.
Francis Leonard Deepak Alvaro Mayoral Miguel Jose Yacaman 《Applied Physics A: Materials Science & Processing》2009,96(4):861-867
The structural transformation of MoO3 nanobelts into MoS2 nanotubes using a simple sulfur source has been reported. This transformation has been extensively investigated using electron
microscopic and spectroscopic techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM),
high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and energy-dispersive X-ray analysis
(SEM-EDAX and TEM-EDX). The method described in this report will serve as a generic route for the transformation of other
oxide nanostructures into the chalcogenide nanostructures. 相似文献
56.
J.-F. Pascual-Sánchez A. San Miguel F. Vicente 《General Relativity and Gravitation》2004,36(9):2075-2083
We analyze the geometry of a rotating disk with a tangential acceleration in the framework of the theory of Special Relativity, using the kinematic linear differential system that verifies the relative position vector of time-like curves in a Fermi reference. A numerical integration of these equations for a generic initial value problem is made up and the results are compared with those obtained in other works. 相似文献
57.
Camarero J Sort J Hoffmann A García-Martín JM Dieny B Miranda R Nogués J 《Physical review letters》2005,95(5):057204
The magnetization reversal in exchange-biased ferromagnetic-antiferromagnetic (FM-AFM) bilayers is investigated. Different reversal pathways on each branch of the hysteresis loop, i.e., asymmetry, are obtained both experimentally and theoretically when the magnetic field is applied at certain angles from the anisotropy direction. The range of angles and the magnitude of this asymmetry are determined by the ratio between the FM anisotropy and the interfacial FM-AFM exchange anisotropy. The occurrence of asymmetry is linked with the appearance of irreversibility, i.e., finite coercivity, as well as with the maximum of exchange bias, increasing for larger anisotropy ratios. Our results indicate that asymmetric hysteresis loops are intrinsic to exchange-biased systems and the competition between anisotropies determines the asymmetric behavior of the magnetization reversal. 相似文献
58.
On the framework of coherence theory we discuss the averaged temporal intensity output provided by real-time optical Fourier transformers when the spectral line shape of the stationary source is considered. Some numerical examples are given and the deviations from perfectly monochromatic sources are pointed out. 相似文献
59.
A new nondestructive method for measuring the spatial distribution of chromatic dispersion along an optical fiber is presented. It is based on using Brillouin optical time-domain analysis to probe the power distribution of the four-wave mixing generated by two continuous-wave lasers. The results obtained prove that this new method is capable of providing better performance than comparable techniques. Furthermore, sensing the variations of Brillouin gain maximum produces additional information about the fiber, such as presence of strain and concentration of GeO2. 相似文献
60.
M. Piantek J. Miguel M. Bernien C. Navío A. Krüger B. Priewisch K. Rück-Braun W. Kuch 《Applied Physics A: Materials Science & Processing》2008,93(2):261-266
The adsorption of 3,3′-di(methoxycarbonyl)azobenzene (CMA) on Au(111) and on Cu(001) substrates was studied by X-ray absorption
spectroscopy measurements at the C, N, and O K edges. We find the molecules physisorbed in a planar conformation flat on the Au(111) surface. At higher coverages, a molecular
crystal is formed wherein the molecules have the same flat geometry. On Cu(001), additional chemical bonds are formed between
the molecules and the surface via the nitrogen atoms. Here the methyl benzoate moieties are tilted out of the surface plane. 相似文献