全文获取类型
收费全文 | 139413篇 |
免费 | 13385篇 |
国内免费 | 7098篇 |
专业分类
电工技术 | 9888篇 |
技术理论 | 11篇 |
综合类 | 15558篇 |
化学工业 | 9867篇 |
金属工艺 | 8150篇 |
机械仪表 | 10151篇 |
建筑科学 | 37318篇 |
矿业工程 | 7194篇 |
能源动力 | 6153篇 |
轻工业 | 1704篇 |
水利工程 | 8330篇 |
石油天然气 | 6104篇 |
武器工业 | 3254篇 |
无线电 | 8322篇 |
一般工业技术 | 8654篇 |
冶金工业 | 3675篇 |
原子能技术 | 1470篇 |
自动化技术 | 14093篇 |
出版年
2024年 | 442篇 |
2023年 | 1448篇 |
2022年 | 3196篇 |
2021年 | 3634篇 |
2020年 | 3803篇 |
2019年 | 2643篇 |
2018年 | 2738篇 |
2017年 | 3598篇 |
2016年 | 4666篇 |
2015年 | 5275篇 |
2014年 | 12293篇 |
2013年 | 8735篇 |
2012年 | 11507篇 |
2011年 | 12345篇 |
2010年 | 9796篇 |
2009年 | 9942篇 |
2008年 | 9096篇 |
2007年 | 10791篇 |
2006年 | 8730篇 |
2005年 | 6789篇 |
2004年 | 5875篇 |
2003年 | 4796篇 |
2002年 | 3809篇 |
2001年 | 3008篇 |
2000年 | 2383篇 |
1999年 | 1800篇 |
1998年 | 1358篇 |
1997年 | 1099篇 |
1996年 | 962篇 |
1995年 | 763篇 |
1994年 | 617篇 |
1993年 | 411篇 |
1992年 | 326篇 |
1991年 | 241篇 |
1990年 | 210篇 |
1989年 | 177篇 |
1988年 | 114篇 |
1987年 | 59篇 |
1986年 | 85篇 |
1985年 | 52篇 |
1984年 | 55篇 |
1983年 | 42篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1959年 | 21篇 |
1951年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 643 毫秒
181.
浅议城市违章建筑的危害 总被引:1,自引:0,他引:1
介绍了违章建筑的概念,分析了违章建筑的危害,从政府管理缺位、经济发展的要求及执法问题三方面,探讨了违章建筑的成因,提出了相关的处理建议。 相似文献
182.
Triple tangent flank milling of ruled surfaces 总被引:3,自引:0,他引:3
Cornelia Menzel 《Computer aided design》2004,36(3):289-296
This paper presents a positioning strategy for flank milling ruled surfaces. It is a modification of a positioning method developed by Bedi et al. [Comput Aided Des 35 (2003) 293]. A cylindrical cutting tool is initially positioned tangential to the two boundary curves on a ruled surface. Optimization is used to move these tangential points to different curves on the ruled surface to reduce the error. A second optimization step is used to additionally make the tool tangent to a rule line, further reducing the error and resulting in a tool position, where the tool is positioned tangential to two guiding rails and one rule line. The resulting surface has 88% less under cutting than the method of Bedi et al. 相似文献
183.
Until recently, numerical simulations of discontinuities in highly super-Alfvénic plasmas have been severely limited by comparatively crude resolution and accuracy. Significant progress in the numerical simulation of such plasmas was achieved with the recently implemented Central Weighted Essentially Non-Oscillatory (CWENO) scheme. Combining this technique with that of adaptive mesh refinement (AMR), we have developed a third-order numerical scheme, which is able to efficiently capture strong gradients on spatial scales being small compared to the overall scale of the plasma system considered. Here, we first describe important algorithmic aspects of the scheme as well as the physics included in it. Second, we present the results of various performance tests. And, third, we illustrate its application to ‘real world problems’ using the example of the dynamics of a Sedov-type explosion. 相似文献
184.
185.
186.
187.
The changes in surface composition of metallic alloys caused by segregation can be very efficiently studied by low-energy ion scattering (LEIS) due to the specific surface sensitivity of this technique. Investigations of single-crystal surfaces of ordered alloys are of particular interest because they provide the possibility to investigate the interplay between segregation effects and the order-disorder phase transition when passing through the transition temperature. Exemplifying these effects for bimetallic alloys we consider in particular the CuAu-system.For the quantitative interpretation of energy and angle resolved LEIS intensity distributions we compare experimental results with those from numerical simulations using the MARLOWE code which we extended with a detailed trajectory analysis. This allows us to apply various discrimination criteria, such as number of collisions, distance of closest approach, identification of the scattering crystal layer, total path length, etc. On this basis structural effects, ion survival probabilities and the influence of thermal vibrations can be studied.We demonstrate this potential by using CuAu(1 0 0) as a special example. The scattering potential parameters were calibrated with elemental single crystals of known structures and the anisotropic Debye temperatures taken from the literature showed good agreement, neutralization was of minor importance in this case. Our procedure could be successfully used for the quantitative analysis of the composition of the first and second layer as a function of temperature. These results are in good agreement with theoretical predictions. 相似文献
188.
A. F. Kurbatskii 《High Temperature》2004,42(1):79-87
The difference in the turbulent diffusion between the active (heat) and passive (mass) scalars in a thermally stably stratified medium is investigated. The axisymmetric problem is treated on the formation of a turbulent circulation flow above a heated disk and on the turbulent diffusion of a passive scalar (impurity) from a continuous surface source in a stably stratified medium. The results indicate that the thermal stratification causes appreciable differences in the coefficients of turbulent transfer between the active (heat) and passive (mass) scalars. This means that the assumption of the identity of the coefficient of turbulent diffusion of heat and mass, employed in conventional models of turbulence, produces significant errors in estimating the heat and mass transfer in a thermally stably stratified medium. 相似文献
189.
190.
Yen-Cho ChenJ.N. Chung 《Computers & Fluids》2003,32(6):795-822
This study intends to provide an increased understanding of the laminar-turbulent transition phenomena for the buoyancy-assisted heated vertical channel flow during the early transient stage. The spectral method with weak formulation is applied in the direct numerical simulation. Initial disturbances consist of the finite-amplitude two-dimensional TS wave and a pair of three-dimensional oblique waves for the K-type disturbances. The results from the harmonic energy competitions of different wave modes show that for the buoyancy-assisted heated flow, the (kx=1, kz=1) or (1,1) and (1,0) modes would gain energy immediately and start to rise at almost the same rate. This phenomenon is different from that of the buoyancy-opposed flow, where the (1,1) mode decays slowly in the beginning until other modes gain enough energy and then it begins to grow quickly and overtakes the (1,0) mode after a short time period. These different transition patterns match with the experimental results that the flow transition is supercritical and subcritical for the buoyancy-assisted and -opposed flows, respectively. Buoyancy-assisted heated flow transition follows the general trend of an isothermal flow in the beginning, but the thermal-buoyant force is crucial in accelerating the instability and also causing notable differences during the subsequent transition process. All of the results for the vortex structures development, kinetic energy budget of the disturbances, flow visualization by tagged fluid particles, and the local temperature fluctuations are consistent in pointing to a clear pattern for the buoyancy-assisted heated flow transition. 相似文献