全文获取类型
收费全文 | 16637篇 |
免费 | 917篇 |
国内免费 | 752篇 |
专业分类
电工技术 | 719篇 |
综合类 | 357篇 |
化学工业 | 3310篇 |
金属工艺 | 1637篇 |
机械仪表 | 1443篇 |
建筑科学 | 488篇 |
矿业工程 | 787篇 |
能源动力 | 563篇 |
轻工业 | 385篇 |
水利工程 | 116篇 |
石油天然气 | 276篇 |
武器工业 | 89篇 |
无线电 | 1011篇 |
一般工业技术 | 2817篇 |
冶金工业 | 417篇 |
原子能技术 | 302篇 |
自动化技术 | 3589篇 |
出版年
2024年 | 20篇 |
2023年 | 212篇 |
2022年 | 365篇 |
2021年 | 406篇 |
2020年 | 435篇 |
2019年 | 390篇 |
2018年 | 424篇 |
2017年 | 551篇 |
2016年 | 537篇 |
2015年 | 568篇 |
2014年 | 897篇 |
2013年 | 1132篇 |
2012年 | 933篇 |
2011年 | 1562篇 |
2010年 | 1013篇 |
2009年 | 1188篇 |
2008年 | 1096篇 |
2007年 | 990篇 |
2006年 | 927篇 |
2005年 | 795篇 |
2004年 | 610篇 |
2003年 | 526篇 |
2002年 | 485篇 |
2001年 | 306篇 |
2000年 | 306篇 |
1999年 | 289篇 |
1998年 | 279篇 |
1997年 | 218篇 |
1996年 | 150篇 |
1995年 | 160篇 |
1994年 | 132篇 |
1993年 | 73篇 |
1992年 | 67篇 |
1991年 | 72篇 |
1990年 | 36篇 |
1989年 | 30篇 |
1988年 | 34篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
An online beam dynamics simulator is being developed for use in the operation of an ion linear particle accelerator. By employing Graphics Processing Unit (GPU) technology, the performance of the simulator has been significantly increased over that of a single CPU and is therefore viable in the demanding accelerator operations environment. Once connected to the accelerator control system, it can rapidly respond to any control set point changes and predict beam properties along an ion linear accelerator in pseudo-real time. This simulator will be a virtual beam diagnostic tool which is especially useful when direct beam measurements are not available. Details about the code structure design, physics algorithms, GPU implementations, and performance are presented. 相似文献
72.
《Expert systems with applications》2014,41(5):2134-2143
In this paper, a hybrid method for optimization is proposed, which combines the two local search operators in chemical reaction optimization with global search ability of for global optimum. This hybrid technique incorporates concepts from chemical reaction optimization and particle swarm optimization, it creates new molecules (particles) either operations as found in chemical reaction optimization or mechanisms of particle swarm optimization. Moreover, some technical bound constraint handling has combined when the particle update in particle swarm optimization. The effects of model parameters like InterRate, γ, Inertia weight and others parameters on performance are investigated in this paper. The experimental results tested on a set of twenty-three benchmark functions show that a hybrid algorithm based on particle swarm and chemical reaction optimization can outperform chemical reaction optimization algorithm in most of the experiments. Experimental results also indicate average improvement and deviate over chemical reaction optimization in the most of experiments. 相似文献
73.
74.
Carbon nanotubes prepared by a classical CVD method with a nickel catalyst have been characterized, then used as conducting anisometric objects dispersed into a polymeric matrix. In a first part, these nanotubes are structurally characterized before and after heat treatments (HTT=1500, 2000, 2500 °C). Diffusion Raman experiments and diamagnetic susceptibility experiments demonstrated their limited graphitized structures.Then, in a second step, a well defined processing way to prepare nanocomposites with a standard epoxy resin is presented. In particular, the use or not of a non-ionic surfactant (Tergitol) to disperse these nanotubes is analyzed. The influence of nanotube contents is examined on the bulk nanocomposite density, the glass transition temperature of the nanocomposites, and the d.c. electrical conductivity behavior. These results demonstrated that the interfacial properties are playing a fundamental role. On one hand, the glass transition temperature is increasing with the nanotube content, and on the other hand, the percolation threshold is found for a rather high critical volumic concentration. Finally, it is demonstrated that a pure geometrical model is not sufficient to explain these behaviors and that a wrapping effect of the organic matrix around the nanotubes has to be considered. 相似文献
75.
Synthesis and characteristics of carbon encapsulated magnetic nanoparticles produced by a hydrothermal reaction 总被引:2,自引:0,他引:2
A novel process to synthesize carbon encapsulated magnetic nanoparticles was developed by heating an aqueous glucose solution containing Fe@Au (Au coated Fe nanoparticles) or Ni nanoparticles at 160–180 °C for 2 h. In comparison with traditional methods, such a hydrothermal approach is not only simple but also able to provide functional groups such as –OH on the surface of carbon sphere. Only pure Fe nanoparticles did not favor the formation of carbon encapsulated magnetic nanoparticles due to the oxidation of Fe nanoparticles by H2O during the reaction and their surfaces had to be coated by an Au shell in advance. The results of TEM, HRTEM, XRD, XPS and vibration sample magnetometer characterization show that uniform carbon spheres containing some embedded Fe@Au nanoparticles with a saturation of 14.6 emu/g are obtained and the size of a typical product is 200 nm. Carbon encapsulated Ni nanoparticles have been successfully prepared in the same way. 相似文献
76.
This work presents experimental results on pickup velocity (critical velocity) measurements for a variety of particulate solids. The present experiments together with previously published experiments of a number of researchers encompass about 100 measurements of 24 materials for a wide range of particle sizes, shapes and densities. Based on the experimental results, three zones are defined by establishing simple relationships between the Reynolds and Archimedes numbers. The empirical relationships were further modified by taking into account the pipe diameter and particle shape (sphericity). The three-zone model was shown to reasonably correlate to Geldart's classification groups. 相似文献
77.
《Expert systems with applications》2014,41(14):6459-6466
Metaheuristic optimization algorithms have become a popular choice for solving complex problems which are otherwise difficult to solve by traditional methods. However, these methods have the problem of the parameter adaptation and many researchers have proposed modifications using fuzzy logic to solve this problem and obtain better results than the original methods. In this study a comprehensive review is made of the optimization techniques in which fuzzy logic is used to dynamically adapt some important parameters in these methods. In this paper, the survey mainly covers the optimization methods of Particle Swarm Optimization (PSO), Gravitational Search Algorithm (GSA), and Ant Colony Optimization (ACO), which in the last years have been used with fuzzy logic to improve the performance of the optimization methods. 相似文献
78.
79.
A new approach is presented for the characterization of particle motion in fluid-solid systems based on dynamic imaging with a gamma scintillation camera. A two-dimensional spouted bed of 200-500 micron diameter anion exchange resin beads was used as a test system. One or several beads were radiolabeled with the 140 keV gamma emitting radionuclide 99m-Tc pertechnetate, and particle velocity, panicle path, the spatial distribution of particle residence times, and local bed density were determined from the measured temporal and spatial distributions of particle activity. While care must be exercised in the interpretation of data when the scale for changes in the spatial distribution of activity approaches the limits of camera resolution, the method is quantitative, non-invasive, and well suited to the study of systems having symmetry in one spatial dimension. 相似文献
80.
Different types of solid bodies (particles) with specific shape and size are needed for industrial processes. For spherical particles, ‘sizer’ measurements are usually reported as sphere diameters. For non-spherical particles, particle shape and especially orientation must be taken into account. Particles of a specific shape will present different views when looked at from different directions.We have employed a Camsizer® instrument to measure the distribution of projected area under different physical conditions for solid cylindrical particles:
- •
- Under ‘ideal’ conditions, corresponding to a uniform distribution of particle orientation, measurements agreed with predictions. The celebrated theorem of Cauchy applies only to this case.
- •
- For two other situations, measured and predicted results differed. However, from the experimental data it was possible to infer the particle orientations and hence theoretically predict the projected area distribution. Excellent agreement between theory and practice was then restored.