全文获取类型
收费全文 | 8400篇 |
免费 | 1158篇 |
国内免费 | 926篇 |
专业分类
电工技术 | 321篇 |
综合类 | 1313篇 |
化学工业 | 229篇 |
金属工艺 | 275篇 |
机械仪表 | 754篇 |
建筑科学 | 1028篇 |
矿业工程 | 322篇 |
能源动力 | 175篇 |
轻工业 | 113篇 |
水利工程 | 368篇 |
石油天然气 | 182篇 |
武器工业 | 119篇 |
无线电 | 1752篇 |
一般工业技术 | 1111篇 |
冶金工业 | 152篇 |
原子能技术 | 69篇 |
自动化技术 | 2201篇 |
出版年
2024年 | 19篇 |
2023年 | 85篇 |
2022年 | 146篇 |
2021年 | 181篇 |
2020年 | 262篇 |
2019年 | 241篇 |
2018年 | 227篇 |
2017年 | 278篇 |
2016年 | 329篇 |
2015年 | 379篇 |
2014年 | 555篇 |
2013年 | 480篇 |
2012年 | 638篇 |
2011年 | 698篇 |
2010年 | 518篇 |
2009年 | 548篇 |
2008年 | 537篇 |
2007年 | 584篇 |
2006年 | 546篇 |
2005年 | 463篇 |
2004年 | 379篇 |
2003年 | 375篇 |
2002年 | 312篇 |
2001年 | 291篇 |
2000年 | 243篇 |
1999年 | 224篇 |
1998年 | 142篇 |
1997年 | 138篇 |
1996年 | 115篇 |
1995年 | 105篇 |
1994年 | 77篇 |
1993年 | 72篇 |
1992年 | 69篇 |
1991年 | 57篇 |
1990年 | 39篇 |
1989年 | 27篇 |
1988年 | 27篇 |
1987年 | 24篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1963年 | 2篇 |
1957年 | 1篇 |
1956年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
An ultrasonic tomographic velocimeter to provide quantitative images of axial flow fields in pipes is developed and presented in this work. To detect the flow in various directions and positions, a novel transducer configuration strategy is proposed. All-in-one transducers are mounted in two sectional planes of the pipe. In each plane, N transducers are equally spaced along the circumference. Overlapped propagation paths are introduced by the configuration strategy, and the influence of the vortex flow can be eliminated theoretically by averaging the line velocities of the overlapped paths. To achieve a fast detection speed, the projection data is collected via an electrical scan in a fan-beam mode. After rearrangement and interpolation of the projection data, the parallel beam filtered back projection (FBP) algorithm is implemented to reconstruct the axial flow field. Numerical simulations with the theoretical velocity profiles were performed. The compensation method for the vortex flow is proved to be effective and necessary, and the number of transducers required for reconstruction of common flow profiles was estimated. Accordingly, an ultrasonic tomographic velocimeter consisting of 2×12 transducers was fabricated. Experiments were conducted in the straight pipe and downstream of a single bend pipe and compared with the computational fluid dynamics (CFD) simulation results. As demonstrated, the ultrasonic tomographic velocimeter was capable of visualizing both symmetric and asymmetric axial flow fields with high reliability. 相似文献
3.
Fatemeh Abdi 《Optimization methods & software》2019,34(1):25-36
In this paper, we propose a globally convergent BFGS method to solve Variational Inequality Problems (VIPs). In fact, a globalization technique on the basis of the hyperplane projection method is applied to the BFGS method. The technique, which is independent of any merit function, is applicable for pseudo-monotone problems. The proposed method applies the BFGS direction and tries to reduce the distance of iterates to the solution set. This property, called Fejer monotonicity of iterates with respect to the solution set, is the basis of the convergence analysis. The method applied to pseudo-monotone VIP is globally convergent in the sense that subproblems always have unique solutions, and the sequence of iterates converges to a solution to the problem without any regularity assumption. Finally, some numerical simulations are included to evaluate the efficiency of the proposed algorithm. 相似文献
4.
《Displays》2015
Multi-projector displays allow the realization of large and immersive projection environments by allowing the tiling of projections from multiple projectors. Such tiled displays require real time geometrical warping of the content that is being projected from each projector. This geometrical warping is a computationally intensive operation and is typically applied using high-end graphics processing units (GPUs) that are able to process a defined number of projector channels. Furthermore, this limits the applicability of such multi-projector display systems only to the content that is being generated using desktop based systems. In this paper we propose a platform independent FPGA based scalable hardware architecture for geometric correction of projected content that allows addition of each projector channel at a fractional increase in logic area. The proposed scheme provides real time correction of HD quality video streams and thus enables the use of this technology for embedded and standalone devices. 相似文献
5.
A double optimal projection method that involves projections for intra-cluster and inter-cluster dimensionality reduction are proposed for video fingerprinting. The video is initially set as a graph with frames as its vertices in a high-dimensional space. A similarity measure that can compute the weights of the edges is then proposed. Subsequently, the video frames are partitioned into different clusters based on the graph model. Double optimal projection is used to explore the optimal mapping points in a low-dimensional space to reduce the video dimensions. The statistics and geometrical fingerprints are generated to determine whether a query video is copied from one of the videos in the database. During matching, the video can be roughly matched by utilizing the statistics fingerprint. Further matching is thereafter performed in the corresponding group using geometrical fingerprints. Experimental results show the good performance of the proposed video fingerprinting method in robustness and discrimination. 相似文献
6.
针对反射面成型的复杂影响因素,提出平面桁架构建的定日镜面形支撑结构优化技术路线. 利用模拟仿真、数值计算和优化算法等方法,解析20 m2定日镜面形定义技术路线的4个组成环节:面形规格及宽高比、上弦杆的截面矩、平面桁架组间距的最优值、机加工中工艺控制要点的量化. 试制小型定日镜进行实验,分析光斑形状和能流密度分布特性,并与理想球面形光斑比较,两者的拟合优度大于0.98. 实验结果表明,当反射镜宽高比取1.2,上弦杆截面矩取40 000 mm4,桁架组间距取950 mm,上弦杆和斜杆的开孔公差小于0.9 mm时,反射面形的质量提升. 研究从原理和实践上证明了该优化技术路线的可行性. 相似文献
7.
8.
9.
10.
文章主要讨论了自动交换光网络(ASON)控制平面的两种不同结构:控制平面在网元外部的结构和控制平面部分集成在网元内部的结构,并对这两种结构进行了比较. 相似文献