全文获取类型
收费全文 | 173802篇 |
免费 | 14171篇 |
国内免费 | 10666篇 |
专业分类
电工技术 | 12608篇 |
技术理论 | 8篇 |
综合类 | 16788篇 |
化学工业 | 19437篇 |
金属工艺 | 8822篇 |
机械仪表 | 11540篇 |
建筑科学 | 9238篇 |
矿业工程 | 3871篇 |
能源动力 | 6667篇 |
轻工业 | 9622篇 |
水利工程 | 3955篇 |
石油天然气 | 7066篇 |
武器工业 | 1681篇 |
无线电 | 12742篇 |
一般工业技术 | 22031篇 |
冶金工业 | 5248篇 |
原子能技术 | 2663篇 |
自动化技术 | 44652篇 |
出版年
2024年 | 537篇 |
2023年 | 1861篇 |
2022年 | 3276篇 |
2021年 | 3701篇 |
2020年 | 4339篇 |
2019年 | 3896篇 |
2018年 | 3726篇 |
2017年 | 4270篇 |
2016年 | 5193篇 |
2015年 | 6296篇 |
2014年 | 10082篇 |
2013年 | 10686篇 |
2012年 | 10694篇 |
2011年 | 11590篇 |
2010年 | 8811篇 |
2009年 | 10677篇 |
2008年 | 10242篇 |
2007年 | 11098篇 |
2006年 | 9789篇 |
2005年 | 8310篇 |
2004年 | 6915篇 |
2003年 | 6295篇 |
2002年 | 5878篇 |
2001年 | 4541篇 |
2000年 | 4670篇 |
1999年 | 4064篇 |
1998年 | 3478篇 |
1997年 | 3174篇 |
1996年 | 3203篇 |
1995年 | 3194篇 |
1994年 | 2871篇 |
1993年 | 1846篇 |
1992年 | 1776篇 |
1991年 | 1252篇 |
1990年 | 969篇 |
1989年 | 858篇 |
1988年 | 778篇 |
1987年 | 436篇 |
1986年 | 280篇 |
1985年 | 410篇 |
1984年 | 456篇 |
1983年 | 471篇 |
1982年 | 363篇 |
1981年 | 429篇 |
1980年 | 292篇 |
1979年 | 138篇 |
1978年 | 121篇 |
1977年 | 78篇 |
1976年 | 44篇 |
1975年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
This paper focuses on the configuration design of flexure hinges with a prescribed compliance matrix and preset rotational center position. A new method for the topology optimization of flexure hinges is proposed based on the adaptive spring model and stress constraint. The hinge optimization model is formulated by maximizing the bending displacement with a spring while optimizing the compliance matrix to a prescribed value. To avoid numerical instability, an artificial spring is used as an auxiliary calculation, and a new strategy is developed for adaptively adjusting the spring stiffness according to the prescribed compliance matrix. The maximum stress of flexure hinge is limited by using a normalized P-norm of the effective von Mises stress, and a position constraint of rotational center is proposed to predetermine the position of the rotational center. In addition, to reduce the error of the stress measurement, a simple but effective filtering method is presented to obtain a complete black-and-white design. Numerical examples are used to verify the proposed method. Topology results show that the obtained flexure hinges have the prescribed compliance matrix and preset rotational center position while also meeting the stress requirements. 相似文献
13.
14.
15.
In this work, the longitudinal permeability of squarely packed dual-scale fiber preforms is studied theoretically. These fiber preforms are composed of aligned porous tows and the tows are tightly packed. The effective permeability is calculated as a parallel-like network of intra-tow permeability and inter-tow permeability, which are quantified by Darcy’s law and the inscribed radius between tows, respectively. The jump velocity at the interface between inter-tow fluids and porous tows is considered, as derived by substituting Beavers and Joseph’s correlation into Brinkman’s equation. We further examine the effects of intra-tow permeability on the effective permeability of the fibrous system with three interface conditions: (1) interface velocity = 0, (2) interface velocity = mean intra-tow velocity, and (3) interface velocity = jump velocity. The jump-velocity-based model is found to be closest to numerical data. The influence of the fiber volume fraction of tows on the effective permeability is also analyzed. 相似文献
16.
基于神经网络和遗传算法的锭子弹性管性能优化 总被引:1,自引:0,他引:1
为得到减振弹性管对下锭胆的支承弹性和锭子高速运动下的稳定性等性能的最优匹配效率,依据减振弹性管的等效抗弯刚度及底部等效刚度系数公式,利用MatLab数值分析软件构建弹性管抗弯刚度和底部挠度数学模型。首先,结合Isight优化软件基于径向基神经网络构建其近似模型,且使精度达到可接受水平,并以模型的关键结构参数弹性模量、螺距、槽宽、壁厚为设计变量,结合遗传算法对弹性管抗弯刚度和底部挠度进行多目标优化设计,得到Pareto最优解集和Pareto前沿图,确定出减振弹性管结构工艺参数的优化方案。通过对优化数据进行分析发现,该方案在保证减振弹性管弹性的同时,其底部振幅明显减弱。 相似文献
17.
Small group detection and tracking in crowd scenes are basis for high level crowd analysis tasks. However, it suffers from the ambiguities in generating proper groups and in handling dynamic changes of group configurations. In this paper, we propose a novel delay decision-making based method for addressing the above problems, motivated by the idea that these ambiguities can be solved using rich temporal context. Specifically, given individual detections, small group hypotheses are generated. Then candidate group hypotheses across consecutive frames and their potential associations are built in a tree. By seeking for the best non-conflicting subset from the hypothesis tree, small groups are determined and simultaneously their trajectories are got. So this framework is called joint detection and tracking. This joint framework reduces the ambiguities in small group decision and tracking by looking ahead for several frames. However, it results in the unmanageable solution space because the number of track hypotheses grows exponentially over time. To solve this problem, effective pruning strategies are developed, which can keep the solution space manageable and also improve the credibility of small groups. Experiments on public datasets demonstrate the effectiveness of our method. The method achieves the state-of-the-art performance even in noisy crowd scenes. 相似文献
18.
Mahmoud Elsisi 《国际智能系统杂志》2020,35(11):1857-1878
The controller design for the robotic manipulator faces different challenges such as the system's nonlinearities and the uncertainties of the parameters. Furthermore, the tracking of different linear and nonlinear trajectories represents a vital role by the manipulator. This paper suggests an optimal design for the nonlinear model predictive control (NLMPC) based on a new improved intelligent technique and it is named modified multitracker optimization algorithm (MMTOA). The proposed modification of the MTOA is carried out based on opposition-based learning (OBL) and quasi OBL approaches. This modification improves the exploration behavior of the MTOA to prevent it from becoming trapped in a local optimum. The proposed method is applied on the robotic manipulator to track different linear and nonlinear trajectories. The NLMPC parameters are tuned by the MMTOA rather than the trial and error method of the designer. The proposed NLMPC based on MMTOA is compared with the original MTOA, genetic algorithm, and cuckoo search algorithm in literature. The superiority and effectiveness of the proposed controller are confirmed to track different linear and nonlinear trajectories. Furthermore, the robustness of the proposed method is emphasized against the uncertainties of the parameters. 相似文献
19.
20.
The main objective of the present work is to improve the performance of bonded joints in carbon fiber composite structures through introducing Multi-Walled Carbon Nanotubes (MWCNTs) into Epocast 50-A1/946 epoxy, which was primarily developed for joining and repairing of composite aircraft structures. Results from tension characterizations of structural adhesive joints (SAJs) with different scarf angles (5–45°) showed improvement up to 40% compared to neat epoxy (NE)–SAJs. Special attention was considered to investigate the performance of SAJs with 5° scarf angle under different environments. The tensile strength and stiffness of both NE-SAJs and MWCNT/E-SAJs were dramatically decreased at elevated temperature. Water absorption showed a marginal drop of about 2.0% in the tensile strength of the moist SAJs compared to the dry one. Cracks initiation and propagation were detected effectively using instrumented-SAJs with eight strain gauges. The experimental results agree well with the predicted using three-dimensional finite element analysis model. 相似文献