全文获取类型
收费全文 | 12052篇 |
免费 | 858篇 |
国内免费 | 491篇 |
专业分类
电工技术 | 286篇 |
技术理论 | 2篇 |
综合类 | 791篇 |
化学工业 | 1144篇 |
金属工艺 | 1305篇 |
机械仪表 | 3412篇 |
建筑科学 | 262篇 |
矿业工程 | 214篇 |
能源动力 | 168篇 |
轻工业 | 428篇 |
水利工程 | 45篇 |
石油天然气 | 199篇 |
武器工业 | 148篇 |
无线电 | 491篇 |
一般工业技术 | 2286篇 |
冶金工业 | 338篇 |
原子能技术 | 64篇 |
自动化技术 | 1818篇 |
出版年
2024年 | 50篇 |
2023年 | 339篇 |
2022年 | 415篇 |
2021年 | 658篇 |
2020年 | 542篇 |
2019年 | 424篇 |
2018年 | 334篇 |
2017年 | 432篇 |
2016年 | 379篇 |
2015年 | 357篇 |
2014年 | 588篇 |
2013年 | 1117篇 |
2012年 | 670篇 |
2011年 | 528篇 |
2010年 | 397篇 |
2009年 | 443篇 |
2008年 | 438篇 |
2007年 | 595篇 |
2006年 | 660篇 |
2005年 | 632篇 |
2004年 | 570篇 |
2003年 | 504篇 |
2002年 | 474篇 |
2001年 | 393篇 |
2000年 | 309篇 |
1999年 | 271篇 |
1998年 | 182篇 |
1997年 | 133篇 |
1996年 | 141篇 |
1995年 | 104篇 |
1994年 | 73篇 |
1993年 | 69篇 |
1992年 | 40篇 |
1991年 | 38篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 15篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1959年 | 1篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 656 毫秒
11.
《Ceramics International》2022,48(17):24953-24964
12.
The COVID-19 pandemic has disrupted the supply chain for personal protective equipment (PPE) for medical professionals, including N95-type respiratory protective masks. To address this shortage, many have looked to the agility and accessibility of additive manufacturing (AM) systems to provide a democratized, decentralized solution to producing respirators with equivalent protection for last-resort measures. However, there are concerns about the viability and safety in deploying this localized download, print, and wear strategy due to a lack of commensurate quality assurance processes. Many open-source respirator designs for AM indicate that they do not provide N95-equivalent protection (filtering 95% of SARS-CoV-2 particles) because they have either not passed aerosol generation tests or not been tested. Few studies have quantified particle transmission through respirator designs outside of the filter medium. This is concerning because several polymer-based AM processes produce porous parts, and inherent process variation between printers and materials also threaten the integrity of tolerances and seals within the printed respirator assembly. No study has isolated these failure mechanisms specifically for respirators. The goal of this paper is to measure particle transmission through printed respirators of different designs, materials, and AM processes. The authors compare the performance of printed respirators to N95 respirators and cloth masks. Respirators in this study printed using desktop- and industrial-scale fused filament fabrication processes and industrial-scale powder bed fusion processes were not sufficiently reliable for widespread distribution and local production of N95-type respiratory protection. Even while assuming a perfect seal between the respirator and the user’s face, although a few respirators provided >90% efficiency at the 100−300 nm particle range, almost all printed respirators provided <60% filtration efficiency. Post-processing procedures including cleaning, sealing surfaces, and reinforcing the filter cap seal generally improved performance, but the printed respirators showed similar performance to various cloth masks. The authors further explore the process-driven aspects leading to low filtration efficiency. Although the design/printer/material combination dictates the AM respirator performance, the identified failure modes originate from system-level constraints and are therefore generalizable across multiple AM processes. Quantifying the limitations of AM in producing N95-type respiratory protective masks advances understanding of AM systems toward the development of better part and machine designs to meet the needs of reliable, functional, end-use parts. 相似文献
13.
An effective coding approach for multiobjective integrated resource selection and operation sequences problem 总被引:3,自引:1,他引:2
In this paper, we consider an integrated Resource Selection and Operation Sequences (iRS/OS) problem in Intelligent Manufacturing
System (IMS). Several kinds of objectives are taken into account, in which the makespan for orders should be minimized; workloads
among machine tools should be balanced; the total transition times between machines in a local plant should also be minimized.
To solve this multiobjective iRS/OS model, a new two vectors-based coding approach has been proposed to improve the efficiency
by designing a chromosome containing two kinds of information, i.e., operation sequences and machine selection. Using such
kind of chromosome, we adapt multistage operation-based Genetic Algorithm (moGA) to find the Pareto optimal solutions. Moreover
a special technique called left-shift hillclimber has been used as one kind of local search to improve the efficiency of our
algorithm. Finally, the experimental results of several iRS/OS problems indicate that our proposed approach can obtain best
solutions. Further more comparing with previous approaches, moGA performs better for finding Pareto solutions.
Received: May 2005/Accepted: December 2005 相似文献
14.
质量控制图系统的实现及在SMT中的应用 总被引:1,自引:0,他引:1
本文将控制图理论与计算机技术相结合,开发了质量控制图系统.介绍了该系统的设计方案和关键技术问题,并以电子产品制造中监控SMT机的焊膏厚度为例说明了系统的应用. 相似文献
16.
17.
Design and Implementation of a Flexible Manufacturing Control System Using Neural Network 总被引:1,自引:0,他引:1
Magdy M. Abdelhameed Farid A. Tolbah 《International Journal of Flexible Manufacturing Systems》2002,14(3):263-279
Design and implementation of a sequential controller based on the concept of artificial neural networks for a flexible manufacturing system are presented. The recurrent neural network (RNN) type is used for such a purpose. Contrary to the programmable controller, an RNN-based sequential controller is based on a definite mathematical model rather than depending on experience and trial and error techniques. The proposed controller is also more flexible because it is not limited by the restrictions of the finite state automata theory. Adequate guidelines of how to construct an RNN-based sequential controller are presented. These guidelines are applied to different case studies. The proposed controller is tested by simulations and real-time experiments. These tests prove the successfulness of the proposed controller performances. Theoretical as well as experimental results are presented and discussed indicating that the proposed design procedure using Elman's RNN can be effective in designing a sequential controller for event-based type manufacturing systems. In addition, the simulation results assure the effectiveness of the proposed controller to outperform the effect of noisy inputs. 相似文献
18.
分别对高新技术企业与一般工业企业、大型企业与中小型企业进行了对比分析,发现高新技术企业比一般工业企业更有吸收能力,而技术转移对中小企业的影响比大型企业大。对参与技术转移及未参与技术转移的制造业企业进行了比较研究,结果证明有技术转移行为的企业具有更优的创新绩效。 相似文献
19.
Howard T. Moncarz 《Journal of research of the National Institute of Standards and Technology》2002,107(2):193-205
Geometric dimensioning and tolerancing (GD&T) is a method to specify the dimensions and form of a part so that it will meet its design intent. GD&T is difficult to master for two main reasons. First, it is based on complex 3D geometric entities and relationships. Second, the geometry is associated with a large, diverse knowledge base of dimensional metrology with many interconnections. This paper describes an approach to create a dimensional metrology knowledge base that is organized around a set of key concepts and to represent those concepts as virtual objects that can be navigated with interactive, computer visualization techniques to access the associated knowledge. The approach can enable several applications. First is the application to convey the definition and meaning of GD&T over a broad range of tolerance types. Second is the application to provide a visualization of dimensional metrology knowledge within a control hierarchy of the inspection process. Third is the application to show the coverage of interoperability standards to enable industry to make decisions on standards development and harmonization efforts. A prototype system has been implemented to demonstrate the principles involved in the approach. 相似文献
20.
WANG Jianwei WEI Xiaopeng LI Rui 《机械工程学报(英文版)》2008,21(1):111-115
Due to the combinatorial nature of cell formation problem and the characteristics of multi-objective and multi-constrain, a novel method of evolutionary algorithm with preference is proposed. The analytic hierarchy process (AHP) is adopted to determine scientifically the weights of the sub-objective functions. The satisfaction of constraints is considered as a new objective, the ratio of the population which doesn't satisfy all constraints is assigned as the weight of new objective. In addition, the self-adaptation of weights is applied in order to converge more easily towards the feasible domain. Therefore, both features multi-criteria and constrains are dealt with simultaneously. Finally, an example is selected from the literature to evaluate the performance of the proposed approach. The results validate the effectiveness of the proposed method in designing the manufacturing cells. 相似文献