全文获取类型
收费全文 | 5112篇 |
免费 | 447篇 |
国内免费 | 318篇 |
专业分类
电工技术 | 137篇 |
综合类 | 514篇 |
化学工业 | 256篇 |
金属工艺 | 287篇 |
机械仪表 | 708篇 |
建筑科学 | 258篇 |
矿业工程 | 74篇 |
能源动力 | 168篇 |
轻工业 | 61篇 |
水利工程 | 82篇 |
石油天然气 | 214篇 |
武器工业 | 52篇 |
无线电 | 364篇 |
一般工业技术 | 500篇 |
冶金工业 | 64篇 |
原子能技术 | 93篇 |
自动化技术 | 2045篇 |
出版年
2024年 | 8篇 |
2023年 | 54篇 |
2022年 | 69篇 |
2021年 | 78篇 |
2020年 | 110篇 |
2019年 | 138篇 |
2018年 | 103篇 |
2017年 | 130篇 |
2016年 | 141篇 |
2015年 | 169篇 |
2014年 | 231篇 |
2013年 | 314篇 |
2012年 | 243篇 |
2011年 | 344篇 |
2010年 | 258篇 |
2009年 | 308篇 |
2008年 | 300篇 |
2007年 | 340篇 |
2006年 | 314篇 |
2005年 | 282篇 |
2004年 | 239篇 |
2003年 | 209篇 |
2002年 | 212篇 |
2001年 | 158篇 |
2000年 | 170篇 |
1999年 | 127篇 |
1998年 | 122篇 |
1997年 | 102篇 |
1996年 | 74篇 |
1995年 | 73篇 |
1994年 | 82篇 |
1993年 | 64篇 |
1992年 | 50篇 |
1991年 | 49篇 |
1990年 | 29篇 |
1989年 | 38篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 18篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1983年 | 20篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有5877条查询结果,搜索用时 15 毫秒
1.
A Pitot tube is a popular device used for the measurements of flow fields. To control the accuracy of the Pitot tube coefficient, the international standard organization (ISO), the American Society for Testing and Materials (ASTM), and the Japanese Industrial Standards (JIS) issued guidelines that recommended the shape and working conditions of these devices. However, many Pitot tubes on the market do not follow these guidelines. In the present study, various types of Pitot tubes in the market were tested at the National Metrology Institute of Japan (NMIJ) to determine the effects of the geometry and flow characteristics. The results revealed certain limitations in the existing ISO and JIS standards, specifically with regard to the recommended design parameters of the AMCA Pitot tube, the reference coefficient value for the JIS Pitot tube, and the redefinition and limitation of Reynolds numbers pertaining to Pitot tube working conditions. 相似文献
2.
In architectural design, surface shapes are commonly subject to geometric constraints imposed by material, fabrication or assembly. Rationalization algorithms can convert a freeform design into a form feasible for production, but often require design modifications that might not comply with the design intent. In addition, they only offer limited support for exploring alternative feasible shapes, due to the high complexity of the optimization algorithm.We address these shortcomings and present a computational framework for interactive shape exploration of discrete geometric structures in the context of freeform architectural design. Our method is formulated as a mesh optimization subject to shape constraints. Our formulation can enforce soft constraints and hard constraints at the same time, and handles equality constraints and inequality constraints in a unified way. We propose a novel numerical solver that splits the optimization into a sequence of simple subproblems that can be solved efficiently and accurately.Based on this algorithm, we develop a system that allows the user to explore designs satisfying geometric constraints. Our system offers full control over the exploration process, by providing direct access to the specification of the design space. At the same time, the complexity of the underlying optimization is hidden from the user, who communicates with the system through intuitive interfaces. 相似文献
3.
Self-adaptive surface measurements that can reduce data redundancy and improve time efficiency are in high demand in many fields of science and technology. For this purpose, a system implemented with Gaussian process (GP) adaptive sampling is developed. The non-parametric GP model is applied to reconstruct the topography and guide the subsequent sampling position, which is determined from the inference uncertainty estimation. A criterion is proposed to terminate the GP adaptive measurement automatically without any prior model or data of the topography. Experiments on typical surfaces validate the intelligence, adaptability, and high accuracy of the GP method along with the stabilization of the automatic iteration termination. Compared with traditional raster sampling, data redundancy is reduced and the time efficiency is improved without sacrificing the surface reconstruction accuracy. The proposed method can be implemented in other systems with similar measurement principles, thus benefitting surface characterizations. 相似文献
4.
Bezier曲线树 总被引:2,自引:0,他引:2
王晓东 《计算机辅助设计与图形学学报》1994,6(4):266-270
本文提出Bezier样条曲线树结构用以高效地实现对曲边几何体的各种几何运算。对任意一条Bezier样条曲线,用deCasteljau算法进行分割后,将分割结果用一平衡二叉树来存储。此后,对于该曲线所作的各种几何运算可以一种逼近等级的方式来进行。先以粗糙的逼近来进行计算,必要时增加精密度,从而提高各种运算的效率。 相似文献
5.
6.
This is the first time an extensive investigation has been carried out regarding the effects of riser exit geometry on pressure drop and solid behaviour inside the Internal Circulating Fluidized Bed (ICFB) riser, using different riser exit geometries at several operating conditions.The Radioactive Particle-Tracking (RPT) technique was used for solid concentration measurements and solid residence time distribution at the exit zone. Experiments were conducted using Geldart B particles, in the gas superficial velocity range of 4 to 10 m/s. Axial solid hold-up, solid residence time distribution in the exit zone, and the reflux ratio factor km, (defined earlier by [E.H. Van der Meer, R.B. Thorpe, J.F. Davidson, Flow patterns in the square cross-section riser of a circulating fluidized bed and the effect of riser exit design, Chem. Eng. Sc. 55 (19) (2000) 4079-4099]), were the main criteria used to investigate the impact of gas-solid separator devices implemented at the ICFB riser exit.Solid residence time distribution results and axial solid hold-up profiles provided clear evidence that the separator device at the riser exit strongly influences the hydrodynamic structure of the ICFB riser. The V-shaped riser exit geometry was found to be the optimum of all the configurations studied. 相似文献
7.
L. M. CRUZ-ORIVE 《Journal of microscopy》2005,219(1):18-28
A new principle is presented to generate isotropic uniform random (IUR) test lines hitting a geometric structure in three-dimensional space (3D). The principle therefore concerns the estimation of surface area, volume, membrane thickness, etc., of arbitrary structures with piecewise smooth boundary. The principle states that a point-sampled test line on an isotropic plane through a fixed point in 3D is effectively an invariant test line in 3D. Particular attention is devoted to the stereology of particles, where an alternative to the surfactor method is obtained to estimate surface area. An interesting case arises when the particle is convex. The methods are illustrated with synthetic examples. 相似文献
8.
Vladlen Koltun 《Information Processing Letters》2004,89(5):233-235
It is an outstanding open problem of computational geometry to prove a near-quadratic upper bound on the number of combinatorial changes in the Voronoi diagram of points moving at a common constant speed along linear trajectories in the plane. In this note we observe that this quantity is Θ(n2) if the points start their movement from a common line. 相似文献
9.
将近年来兴起的小波理论应用于影象分割技术,提出了一种基于影象直方图小波变换的影象分割方法,并从理论上给出了使用该法所得分割门限的物理意义。实例表明,这种由粗到细引导的多分辨率分析方法,对于复杂影象的分割具有较强的鲁棒性和有效性,克服了传统分割方法中的参数需要人工确定的缺点。 相似文献
10.
周培德 《计算机辅助设计与图形学学报》2002,14(3):287-288
周培协三角剖分是否能得到最小权三角剖分,周培德在《周培德三角部分不是最小权三角剖分》一文撰写之前已有新的结论,本文还指出《周培德三角剖分不是最小权三角剖分》一文所举反例不成立。 相似文献