全文获取类型
收费全文 | 17946篇 |
免费 | 2379篇 |
国内免费 | 1424篇 |
专业分类
电工技术 | 1097篇 |
综合类 | 1274篇 |
化学工业 | 3219篇 |
金属工艺 | 3228篇 |
机械仪表 | 951篇 |
建筑科学 | 474篇 |
矿业工程 | 232篇 |
能源动力 | 591篇 |
轻工业 | 1595篇 |
水利工程 | 176篇 |
石油天然气 | 273篇 |
武器工业 | 206篇 |
无线电 | 1962篇 |
一般工业技术 | 2982篇 |
冶金工业 | 1286篇 |
原子能技术 | 1439篇 |
自动化技术 | 764篇 |
出版年
2024年 | 87篇 |
2023年 | 405篇 |
2022年 | 733篇 |
2021年 | 834篇 |
2020年 | 807篇 |
2019年 | 791篇 |
2018年 | 808篇 |
2017年 | 842篇 |
2016年 | 808篇 |
2015年 | 728篇 |
2014年 | 1009篇 |
2013年 | 1261篇 |
2012年 | 1162篇 |
2011年 | 1267篇 |
2010年 | 873篇 |
2009年 | 985篇 |
2008年 | 914篇 |
2007年 | 1173篇 |
2006年 | 1055篇 |
2005年 | 855篇 |
2004年 | 777篇 |
2003年 | 621篇 |
2002年 | 470篇 |
2001年 | 391篇 |
2000年 | 369篇 |
1999年 | 302篇 |
1998年 | 231篇 |
1997年 | 221篇 |
1996年 | 185篇 |
1995年 | 139篇 |
1994年 | 114篇 |
1993年 | 109篇 |
1992年 | 93篇 |
1991年 | 70篇 |
1990年 | 49篇 |
1989年 | 49篇 |
1988年 | 33篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 35篇 |
1981年 | 23篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 2篇 |
1959年 | 3篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Low dielectric constant (low k) carbon-doped silicon oxide (CDO) films are obtained by plasma-enhanced chemical vapor deposition. The k value of the as-deposited CDO film is less than 2.9. However, the k value may be changed during the integration process. In integration process, photoresist removal is commonly implemented with oxygen plasma ashing or by wet chemical stripping. In this work, the impact of oxygen plasma treatment has been investigated on the quality of the low-k CDO films. Different plasma treatment conditions, including variable pressure, r.f. power, and treatment time were employed. A variety of techniques, including X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, time-of-flight secondary ion mass spectrometry (TOF-SIMS), atomic force microscopy (AFM), and scanning electron microscope (SEM) were used to analyze the effect of the oxygen plasma post-treatment on the low-k CDO films. The result indicates that oxygen plasma will damage the CDO film by removing the entire carbon content in the upper part of the film with increasing treatment time, which results in an increase in the k value and film thickness loss. Our result also confirms that with low r.f. power and low pressure, the damage will be less. 相似文献
83.
84.
M. Cemal Genes Suleyman Kocak 《International journal for numerical methods in engineering》2005,62(6):798-823
In this paper, a coupled model based on finite element method (FEM), boundary element method (BEM) and scaled boundary FEM (SBFEM) (also referred to as the consistent infinitesimal finite element cell method) for dynamic response of 2D structures resting on layered soil media is presented. The SBFEM proposed by Wolf and Song (Finite‐element Modelling of Unbounded Media. Wiley: England, 1996) and BEM are used for modelling the dynamic response of the unbounded media (far‐field). The standard FEM is used for modelling the finite region (near‐field) and the structure. In SBFEM, which is a semi‐analytical technique, the radiation condition at infinity is satisfied exactly without requiring the fundamental solution. This method, also eliminates the need for the discretization of interfaces between different layers. In both SBFEM and BEM, the spatial dimension is decreased by one. The objective of the development of this coupled model is to combine advantages of above‐mentioned three numerical models to solve various soil–structure interaction (SSI) problems efficiently and effectively. These three methods are coupled (FE–BE–SBFEM) via substructuring method, and a computer programme is developed for the harmonic analyses of SSI systems. The coupled model is established in such a way that, depending upon the problem and far‐field properties, one can choose BEM and/or SBFEM in modelling related far‐field region(s). Thus, BEM and/or SBFEM can be used efficiently in modelling the far‐field. The proposed model is applied to investigate dynamic response of rigid and elastic structures resting on layered soil media. To assess the proposed SSI model, several problems existing in the literature are chosen and analysed. The results of the proposed model agree with the results presented in the literature for the chosen problems. The advantages of the model are demonstrated through these comparisons. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
85.
Xikui Li Zejia Liu R. W. Lewis 《International journal for numerical methods in engineering》2005,64(5):667-708
A mixed finite element for coupled thermo‐hydro‐mechanical (THM) analysis in unsaturated porous media is proposed. Displacements, strains, the net stresses for the solid phase; pressures, pressure gradients, Darcy velocities for pore water and pore air phases; temperature, temperature gradients, the total heat flux are interpolated as independent variables. The weak form of the governing equations of coupled THM problems in porous media within the element is given on the basis of the Hu–Washizu three‐filed variational principle. The proposed mixed finite element formulation is derived. The non‐linear version of the element formulation is further derived with particular consideration of the THM constitutive model for unsaturated porous media based on the CAP model. The return mapping algorithm for the integration of the rate constitutive equation, the consistent elasto‐plastic tangent modulus matrix and the element tangent stiffness matrix are developed. For geometrical non‐linearity, the co‐rotational formulation approach is utilized. Numerical results demonstrate the capability and the performance of the proposed element in modelling progressive failure characterized by strain localization and the softening behaviours caused by thermal and chemical effects. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
86.
Electron acoustic solitons in collisionless and weakly relativistic plasmas are studied. The Krylov–Bogoliubov–Mitropolsky perturbative technique is employed to obtain the nonlinear Schrodinger wave equation. We have numerically investigated modulational instability for different values of the streaming velocity. Graphs have been plotted to see the change in amplitude and inverse width by varying different plasma parameters. 相似文献
87.
This paper presents a new route about producing carbon black,by wich the natural gas cracking is carried out in the absence of oxygen thanks to an electric energy supply externally given by a plasma jet.The carbon black produced by this process has a narrow size distribution and a small average diameter of 38nm as well as a highly branched aggregate.The higher DBP value of 1.40ml/g shows it should be a high structure carbon black.The FTIR spectra shows that there are lots of aromatic c-c bonds and a large amount of nitrogen-coutaining functional groups on the carbon blacks surface,such as-NH,-CN as we3ll as -CH,-OH,-COOH groups. 相似文献
88.
In this paper, the calculated results about the propagation properties of electromag-netic wave in a plasma slab are described. The relationship of the propagation properties with frequencies of electromagnetic wave, and parameters of plasma (electron temperature, electron density, dimensionless collision frequency and the size of the plasma slab) is analyzed. 相似文献
89.
Abstract The experimental system for electrically exploding single metal wire has been de-signed and manufactured. Expansion of the dense plasma column formed from an electricallyexploding Cu wire of diameter 30 μm has been studied with a high-speed photographer to obtainthe time-dependent radius (R-t) curve. The experimental results demonstrate that the mean ex-pansion rate of the dense plasma column is 1.94 μm/ns, 2.6 μm/ns and 3.75 μm/ns according tothe peak pulse current 4.5 kA, 7 kA and 9.5 kA respectively. The results can be beneficial to givinga profound understanding of the early stage of wire-array Z-pinch physics and to improvement ontheir design. 相似文献
90.
The degradation of benzidine in aqueous solution by the low temperature plasma was examined. The results showed that the concentration of medium and the value of pH have an appreciable effect on the degradation of benzidine. What is more important is that iron ions acting as a catalyst play an important role in this reaction. For exploring the degradation mechanism of benzidine, some of the intermediate products were recorded by HPLC (high performance liquid chromatography). 相似文献