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1.
Nonlinear total variation based noise removal algorithms   总被引:144,自引:0,他引:144  
A constrained optimization type of numerical algorithm for removing noise from images is presented. The total variation of the image is minimized subject to constraints involving the statistics of the noise. The constraints are imposed using Lanrange multipliers. The solution is obtained using the gradient-projection method. This amounts to solving a time dependent partial differential equation on a manifold determined by the constraints. As t → ∞ the solution converges to a steady state which is the denoised image. The numerical algorithm is simple and relatively fast. The results appear to be state-of-the-art for very noisy images. The method is noninvasive, yielding sharp edges in the image. The technique could be interpreted as a first step of moving each level set of the image normal to itself with velocity equal to the curvature of the level set divided by the magnitude of the gradient of the image, and a second step which projects the image back onto the constraint set.  相似文献
2.
Continuous control of chaos by self-controlling feedback   总被引:125,自引:0,他引:125  
K. Pyragas 《Physics Letters A》1992,170(6):421-428
Two methods of chaos control with a small time continuous perturbation are proposed. The stabilization of unstable periodic orbits of a chaotic system is achieved either by combined feedback with the use of a specially designed external oscillator, or by delayed self-controlling feedback without using of any external force. Both methods do not require an a priori analytical knowledge of the system dynamics and are applicable to experiment. The delayed feedback control does not require any computer analyses of the system and can be particularly convenient for an experimental application.  相似文献
3.
Extracting qualitative dynamics from experimental data   总被引:45,自引:0,他引:45  
We consider the notion of qualitative information and the practicalities of extracting it from experimental data. Our approach, based on a theorem of Takens, draws on ideas from the generalized theory of information known as singular system analysis due to Bertero, Pike and co-workers. We illustrate our technique with numerical data from the chaotic regime of the Lorenz model.  相似文献
4.
Stability and bifurcation in a neural network model with two delays   总被引:38,自引:0,他引:38  
A simple neural network model with two delays is considered. Linear stability of the model is investigated by analyzing the associated characteristic transcendental equation. For the case without self-connection, it is found that the Hopf bifurcation occurs when the sum of the two delays varies and passes a sequence of critical values. The stability and direction of the Hopf bifurcation are determined by applying the normal form theory and the center manifold theorem. An example is given and numerical simulations are performed to illustrate the obtained results.  相似文献
5.
The sonochemical degradation of a variety of chemical contaminants in aqueous solution has been investigated. Substrates such as chlorinated hydrocarbons, pesticides, phenols, explosives such as TNT, and esters are transformed into short-chain organic acids, CO2, and inorganic ions as the final products. Time scales of treatment in simple batch reactors over the frequency range of 20 to 500 kHz are reported to range from minutes to hours for complete degradation. Ultrasonic irradiation appears to be an effective method for the rapid destruction of organic contaminants in water because of localized high concentrations of oxidizing species such as hydroxyl radical and hydrogen peroxide in solution, high localized temperatures and pressures, and the formation of transient supercritical water.

The degradation of chemical compounds by acoustic cavitation is shown to involve three distinct pathways: 1) oxidation by hydroxyl radicals, 2) pyrolytic decomposition and 3) supercritical water oxidation. Detailed reaction mechanisms for the degradation of p-nitrophenol, carbon tetrachloride, parathion, p-nitrophenyl acetate and trinitrotoluene are presented.  相似文献

6.
Sonochemical and photochemical oxidation of organic matter   总被引:34,自引:0,他引:34  
Recent developments in sonochemistry have led us to study its use to treat water and wastewater. The effects of ultrasound wave in hydrophilic chemical oxidations are mainly due to hydroxyl radical production during the cavitation-induced water decomposition. Currently, the sonochemical destruction of aromatic compounds in water solution is obtained with low rates. The aim of this work is to evaluate the efficiency of the sonochemical effect in conjunction with a photochemical irradiation. Taking phenol as an example, the combined action of sonochemistry and photochemistry has been considered in a ‘sonuv’ reactor. An important enhancement of the degradation rate of phenol has been observed. It may be the result of three different oxidative processes: direct photochemical action, high frequency sonochemistry and reaction with ozone (produced by UV irradiation of air). The process has been successfully tested to lower the chemical oxygen demand of a municipal wastewater.  相似文献
7.
原子吸收光谱法测定茶叶中7种微量元素   总被引:34,自引:4,他引:30  
用浓硝酸-过氧化氢处理样品,火焰原子吸收光谱法测定江西龙南县映山红茶叶中Fe、Cu、Ca、Mn、Zn 5种微量元素,用石墨炉原子吸收光谱法测定茶叶中Pb、Cd.所测定的茶叶中含有丰富的人体必需的微量元素,Pb、Cd的含量远远低于国家的限定标准,采用此方法回收率在93.70%-102.40%之间,相对标准偏差小于10%.本方法简单、准确,结果令人满意.  相似文献
8.
Closed loop direct metal deposition: art to part   总被引:32,自引:0,他引:32  
The direct metal deposition (DMD) process is drawing considerable contemporary interest due to its capability to deliver “Art to Part”. DMD can reduce the lead time for a concept to product by eliminating several intermediate steps. The most attractive feature of the process is that not only can it produce functional parts but it can also be interfaced with the homogenization design method, heterogeneous solid model and computer aided design software to produce “Designed Material” with desired properties generally not observed in nature. Closed loop DMD is a synthesis of multiple technologies including lasers, sensors, computer numerical controlled work handling stage, CAD/CAM software and cladding metallurgy. This paper describes the methodology used to produce a designed macro- and microstructure and reviews the state of the art for closed loop DMD.  相似文献
9.
Carbon nanotubes: opportunities and challenges   总被引:29,自引:0,他引:29  
Carbon nanotubes are graphene sheets rolled-up into cylinders with diameters as small as one nanometer. Extensive work carried out worldwide in recent years has revealed the intriguing electrical and mechanical properties of these novel molecular scale wires. It is now well established that carbon nanotubes are ideal model systems for studying the physics in one-dimensional solids and have significant potential as building blocks for various practical nanoscale devices. Nanotubes have been shown to be useful for miniaturized electronic, mechanical, electromechanical, chemical and scanning probe devices and materials for macroscopic composites. Progress in nanotube growth has facilitated the fundamental study and applications of nanotubes. Gaining control over challenging nanotube growth issues is critical to the future advancement of nanotube science and technology, and is being actively pursued by researchers.  相似文献
10.
This paper presents a review of the ultrasonically assisted extraction of bioactive principles from herbs. Much of the work was carried out under European community grants under the COPERNICUS programme and in a COST D10 network. Some aspects of classical and non-conventional extraction procedures are also presented and briefly discussed.  相似文献
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