全文获取类型
收费全文 | 67926篇 |
免费 | 10235篇 |
国内免费 | 5771篇 |
专业分类
电工技术 | 7795篇 |
技术理论 | 2篇 |
综合类 | 6943篇 |
化学工业 | 5840篇 |
金属工艺 | 3619篇 |
机械仪表 | 6949篇 |
建筑科学 | 3702篇 |
矿业工程 | 2262篇 |
能源动力 | 3175篇 |
轻工业 | 3619篇 |
水利工程 | 1758篇 |
石油天然气 | 2798篇 |
武器工业 | 938篇 |
无线电 | 5112篇 |
一般工业技术 | 6875篇 |
冶金工业 | 2395篇 |
原子能技术 | 375篇 |
自动化技术 | 19775篇 |
出版年
2024年 | 267篇 |
2023年 | 1536篇 |
2022年 | 2700篇 |
2021年 | 2956篇 |
2020年 | 3196篇 |
2019年 | 2773篇 |
2018年 | 2482篇 |
2017年 | 2984篇 |
2016年 | 3294篇 |
2015年 | 3631篇 |
2014年 | 5162篇 |
2013年 | 5050篇 |
2012年 | 5714篇 |
2011年 | 5831篇 |
2010年 | 4091篇 |
2009年 | 4349篇 |
2008年 | 3838篇 |
2007年 | 4415篇 |
2006年 | 3631篇 |
2005年 | 2949篇 |
2004年 | 2436篇 |
2003年 | 1947篇 |
2002年 | 1661篇 |
2001年 | 1330篇 |
2000年 | 1081篇 |
1999年 | 782篇 |
1998年 | 692篇 |
1997年 | 588篇 |
1996年 | 473篇 |
1995年 | 435篇 |
1994年 | 349篇 |
1993年 | 265篇 |
1992年 | 223篇 |
1991年 | 174篇 |
1990年 | 159篇 |
1989年 | 139篇 |
1988年 | 82篇 |
1987年 | 36篇 |
1986年 | 31篇 |
1985年 | 25篇 |
1984年 | 27篇 |
1983年 | 27篇 |
1982年 | 26篇 |
1981年 | 13篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1975年 | 5篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Shibendu Mahata Rajib Kar Durbadal Mandal 《International Journal of Circuit Theory and Applications》2020,48(9):1554-1560
In this letter, the optimal rational approximation of fractional-order bandpass Butterworth filter (FOBBF) is presented. The transfer function of the FOBBF is decomposed into a multiplication of first-order and second-order terms. As a result, the design stability conditions can be easily satisfied using only the variable boundary constraints. The proposed technique generalizes the symmetric fractional-order roll-off characteristic as only a special case of the asymmetric one. Several examples are presented to validate the modeling efficacy. 相似文献
102.
103.
Shape from focus (SFF) is a widely used passive optical method for 3D shape reconstruction. In SFF, a focus measure, which is used to estimate the relative focus level, plays a critical role in depth estimation. In this article, we present a new focus measure for accurate 3D shape estimation in optical microscopy based on the analysis of 3D structure tensor. First, the 3D tensors are computed from the input image sequence for each pixel. Then, each tensor is decomposed into point, curve, and surface tensors by decomposing tensors into eigenvalues and eigenvectors. Finally, the surfaceness is used to measure the quality of sharpness. The proposed focus measure provides accurate focus values and better resistance against noise. The proposed measure is evaluated by conducting experiments using image sequences of simulated and microscopic real objects. The comparative analysis demonstrates the effectiveness of the proposed focus measure in recovering 3D shape. 相似文献
104.
为提高女性裤装的合体性与舒适性,采用三维测量法、图像测量法及手工测量法相结合的方式,对236名18~25岁的青年女性腿部形态进行测量,获取20个相关特征变量;通过主成分因子分析得到影响腿部形态的主要特征因子,通过聚类分析得到青年女性腿部形态的分类结果;最后结合膝曲角的正负归纳出各类腿部形态的辨别规则并进行辨别验证。研究得出:影响腿部形态的主要特征因子有水平围度因子、长度因子、小腿围度差因子、腿部曲度因子、腿部轮廓因子和大腿围度差因子;人体腿部形态可分成圆体型、稍扁体型和扁体型3类;以大腿宽厚比、大腿根围膝围比、大小腿长比及膝曲角4个变量建立腿部形态分类规则。 相似文献
105.
106.
107.
Multiemotional product color design using gray theory and nondominated sorting genetic algorithm-III
When users select products, they consider the emotional experience resulting from the color of the product. However, the emotional demands of users for product color are multidimensional and diverse. It is very important yet difficult to accurately grasp multiemotional image requirements and effectively convert them into design elements. Therefore, multiemotional product color design (MEPCD) has become a very important and challenging research topic. In this article, a novel MEPCD system using gray theory (GT) and nondominated sorting genetic algorithm-III (NSGA-III) is proposed to effectively solve the MEPCD problem. First, the image perception spaces of users, which exist in different emotional dimensions, were collected using factor analysis and the semantic differential technique. Then, GT was used to establish a multidimensional emotional product color image evaluation model. Finally, NSGA-III was used to optimize and design a multiemotional color scheme for a product. Furthermore, according to actual conditions, an MEPCD system was established based on the proposed method. The design case study shows that the method and design system proposed in this article have a certain range of applicability and can effectively improve the practicality of MEPCD. 相似文献
108.
《International Journal of Hydrogen Energy》2020,45(38):19455-19464
This paper presents a new procedure for optimal allocation and optimal sizing of a battery energy storage system (BESS) for primary frequency support in an isolated power system. For the BESS allocation, a transmission bus system with larger frequency decline is recognized and the BESS sizing is performed by a constrained optimization strategy based on a new modified metaheuristic, called Developed Harris Hawks Optimization (DHHO). The simulation results of the suggested DHHO are compared with Bat Optimization Algorithm (BOA) and Genetic Algorithm (GA) from the literature to show the method efficiency. The final results showed higher precision with lower required iterations for the suggested DHHO method. Also, the proposed DHHO gives lower investment costs for BESS with lower power and energy requirement toward the other compared methods. 相似文献
109.
110.
乙烯裂解炉内复杂物理化学过程耦合模拟与优化能够满足乙烯装置对高效率、低污染和低成本的设计和操作要求,对提高乙烯工业的竞争力具有重要意义。针对简单燃烧机理难以准确预测炉膛燃烧生成NOx浓度分布的弊端,提出了在裂解炉使用更准确的简化GRI-Mesh 3.0机理结合涡耗散概念(EDC)模型的方法,并对Sandia Flame D的燃烧过程进行计算流体力学(CFD)模拟,验证了此耦合模型的可靠性。在已建立的燃烧模型的基础上,研究了助燃空气对降低裂解炉NO排放的影响,结果表明:在满足裂解炉热效率的情况下,空气预热温度为300~600 K、过量空气系数为1.1时降低NO的效果最佳。 相似文献