全文获取类型
收费全文 | 16711篇 |
免费 | 1469篇 |
国内免费 | 1236篇 |
专业分类
电工技术 | 443篇 |
综合类 | 719篇 |
化学工业 | 3094篇 |
金属工艺 | 1872篇 |
机械仪表 | 2285篇 |
建筑科学 | 224篇 |
矿业工程 | 108篇 |
能源动力 | 344篇 |
轻工业 | 799篇 |
水利工程 | 41篇 |
石油天然气 | 246篇 |
武器工业 | 109篇 |
无线电 | 3522篇 |
一般工业技术 | 3630篇 |
冶金工业 | 439篇 |
原子能技术 | 816篇 |
自动化技术 | 725篇 |
出版年
2024年 | 47篇 |
2023年 | 307篇 |
2022年 | 418篇 |
2021年 | 481篇 |
2020年 | 507篇 |
2019年 | 523篇 |
2018年 | 467篇 |
2017年 | 607篇 |
2016年 | 589篇 |
2015年 | 546篇 |
2014年 | 695篇 |
2013年 | 978篇 |
2012年 | 960篇 |
2011年 | 1250篇 |
2010年 | 900篇 |
2009年 | 939篇 |
2008年 | 986篇 |
2007年 | 970篇 |
2006年 | 891篇 |
2005年 | 789篇 |
2004年 | 655篇 |
2003年 | 613篇 |
2002年 | 573篇 |
2001年 | 386篇 |
2000年 | 403篇 |
1999年 | 356篇 |
1998年 | 327篇 |
1997年 | 316篇 |
1996年 | 295篇 |
1995年 | 229篇 |
1994年 | 177篇 |
1993年 | 177篇 |
1992年 | 155篇 |
1991年 | 139篇 |
1990年 | 127篇 |
1989年 | 119篇 |
1988年 | 83篇 |
1987年 | 74篇 |
1986年 | 64篇 |
1985年 | 62篇 |
1984年 | 70篇 |
1983年 | 57篇 |
1982年 | 58篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The inherently nonlinear phenomenon of fatigue crack propagation is modeled as a linear random process. To a first approximation, simple, nonstationary time series models are introduced and standard techniques for determining the parameters of autoregressive integrated moving-average processes are applied. Multiplicative time series models are next utilised for the representation of a group of crack history curves. Implementation of the models on the Virkler experimental data set yields satisfactory results. Reliable Gaussian approximations to the distribution of the time required by a crack to reach a specified critical length are obtained, and the usefulness of the approach is demonstrated when updating lifetime predictions after periodic inspections. 相似文献
52.
环境因子的定义及研究现状 总被引:12,自引:0,他引:12
胡斌 《太赫兹科学与电子信息学报》2003,1(1):88-92
从普遍接受的三个基本假设出发,讨论环境因子的定义和失效机理不变的约束条件,重点综述环境因子的研究现状和常用方法,并探讨引入反应论模型解决环境因子预测问题的可能途径。 相似文献
53.
54.
T. MANN B. W. TVEITEN G. HÄRKEGÅRD 《Fatigue & Fracture of Engineering Materials & Structures》2006,29(2):113-122
The fatigue life of a welded aluminium T‐joint made from beams with rectangular hollow section (RHS) has been predicted using a crack propagation analysis and compared with experimental results from joints with different residual stress levels. To include the effect of the residual stresses, the stress ratio was calculated at the weld toe and, via Walker's equation, introduced into the analysis. How to obtain the Walker exponent has been discussed in detail. The introduction of a stress ratio at the weld toe provides good agreement between the experimentally and analytically found S–N curves. The effect of the residual stress was successfully included in the analysis. 相似文献
55.
ABSTRACT: The thermal evolution behavior of the organic free radicals induced in irradiated black pepper was studied by electron spin resonance spectroscopy. To analyze the time-dependent evolution process, we used the theory of transient phenomena, that is, an ordinal differential equation, as well as the nonlinear least squares numerical method. We found that the radical evolution that occurred in the irradiated pepper obeys a single exponential function and yields a unique time constant. The evolution of the organic free radical undergoes a simple reaction process of a single radical species. 相似文献
56.
Ying‐Hung So 《Polymer International》2006,55(2):127-138
Poly(2,4‐dimethyl‐1,4‐phenylene oxide) (PPO), poly(benzo[1,2‐d:5,4‐d′]bisoxazole‐2,6‐diyl‐1,4‐phenylene) (PBO) and poly(benzo[1,2‐d:4,5‐d′]bisthiazole‐2,6‐diyl‐1,4‐phenylene) (PBZT), which are polymers with extended conjugated structures, undergo a self‐sensitized photo‐induced electron‐transfer reaction. A second component is not required. This article presents many similar observations on these polymers when they are exposed to light and evidence to support the proposed photo‐induced electron‐transfer mechanism. Methods to stabilize these polymers against photo‐oxidation are also described. Workers investigating other conjugated polymeric systems may find the experimental methods, observations and polymer stabilization approaches discussed in this review useful. Copyright © 2005 Society of Chemical Industry 相似文献
57.
Composite films composed of poly(methyl methacrylate‐co‐butyl acrylate) (PMMABA) and nematic‐type liquid crystals E7 and E8 (commercial products from E. Merck, Darmstadt, Germany) were prepared through solvent casting in chloroform. The morphology and electrooptic responses were studied. Scanning electron microscopy observations showed that the liquid‐crystal phase (E7 or E8), as larger, elongated, interconnected cavities, was continuously embedded in a spongelike PMMABA matrix. At a specific level of the liquid‐crystal (E7 or E8) loading (30/70 wt %), the effects of the voltage, temperature, and frequency of an applied alternating‐current electric field on the transmittance of the composite films were measured with a He–Ne laser (wavelength = 632.8 nm). The results were interpreted in terms of the aggregation structure, interfacial interaction, and solubility of the liquid crystal in the matrix polymer. The results indicated that, under these experimental conditions, the output could be controlled to a desired level by the selection of suitable liquid crystals to prepare polymer‐dispersed liquid‐crystal, electrooptic, active composite films with a response time of the order of only milliseconds or less. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
58.
Experiments on the effect of temperature on the optical and electro-optical behaviors of polymer-dispersed liquid crystals (PDLCs) are considered. Composite films composed of poly(methyl methacrylate) (PMMA) and the nematic-type liquid crystal (LC) E7 were prepared by solvent casting in chloroform. The PDLC film contained droplets of E7 from 10 to 80 wt % in a PMMA matrix. Morphological studies illustrated the formation of isolated droplets of LC due to phase separation, and their homogeneous distribution increased with increasing E7 content. Thermo-optical studies showed an increase in the nematic–isotropic transition temperature of composites, which indicated preferential solvation during the phase-separation process. The electro-optical characteristics were studied under the conditions of an externally applied square wave electric field with a He–Ne laser (λ = 632.8 nm) as a light source. The responses improved as the E7 content in PMMA increased. Semipermanent memory effects were noticed in composites at higher temperatures. Changes in the transmittance due to thermal variations provided the possibility of using such a device as a temperature sensor. The results obtained indicate that under these experimental conditions, the output can be controlled to the desired level by the selection of a suitable loading of LC to prepare PDLC electro-optically active composite films with a response time on the order of only a few milliseconds. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
59.
60.
S. Zaefferer 《Advanced Engineering Materials》2003,5(8):607-613
In recent years the investigation of local texture and microstructure by analysis of electron backscatter diffraction patterns (EBSP) in the SEM has become a very powerful and popular method. With the introduction of SEM with field emission guns (FEG) the spatial resolution of EBSP measurements could be enhanced from 500 nm with a tungsten emitter to better than 50 nm. This evolution of SEM techniques raises the question whether transmission electron microscopy (TEM) still has fields of application in texture research. The present article answers this question with a clear “yes” and presents three examples of investigations where TEM is indispensable. The three examples comprise the investigation of the correlation between dislocation structure and deformation texture, a study on nucleation mechanisms of recrystallization in highly deformed metals and the investigation of microtexture and microstructure in nanocrystalline materials. Together with the presentation of these cases some of the necessary measurement techniques are described briefly. It is shown that TEM has to be applied when highest spatial resolution of orientation determination and imaging and high accuracy of orientation determination are to be reached, when the three‐dimensional and quantitative characterization of lattice defects is required or when materials with a high density of lattice defects are to be investigated. 相似文献