全文获取类型
收费全文 | 28151篇 |
免费 | 2336篇 |
国内免费 | 1725篇 |
专业分类
电工技术 | 767篇 |
技术理论 | 1篇 |
综合类 | 1969篇 |
化学工业 | 1055篇 |
金属工艺 | 1068篇 |
机械仪表 | 1719篇 |
建筑科学 | 2541篇 |
矿业工程 | 636篇 |
能源动力 | 719篇 |
轻工业 | 396篇 |
水利工程 | 288篇 |
石油天然气 | 349篇 |
武器工业 | 324篇 |
无线电 | 3660篇 |
一般工业技术 | 2175篇 |
冶金工业 | 549篇 |
原子能技术 | 292篇 |
自动化技术 | 13704篇 |
出版年
2024年 | 67篇 |
2023年 | 269篇 |
2022年 | 471篇 |
2021年 | 641篇 |
2020年 | 681篇 |
2019年 | 507篇 |
2018年 | 577篇 |
2017年 | 715篇 |
2016年 | 837篇 |
2015年 | 867篇 |
2014年 | 1583篇 |
2013年 | 1446篇 |
2012年 | 1684篇 |
2011年 | 2072篇 |
2010年 | 1450篇 |
2009年 | 1495篇 |
2008年 | 1757篇 |
2007年 | 2157篇 |
2006年 | 2005篇 |
2005年 | 1905篇 |
2004年 | 1646篇 |
2003年 | 1457篇 |
2002年 | 1132篇 |
2001年 | 869篇 |
2000年 | 714篇 |
1999年 | 601篇 |
1998年 | 492篇 |
1997年 | 382篇 |
1996年 | 324篇 |
1995年 | 284篇 |
1994年 | 200篇 |
1993年 | 154篇 |
1992年 | 106篇 |
1991年 | 87篇 |
1990年 | 70篇 |
1989年 | 67篇 |
1988年 | 58篇 |
1987年 | 42篇 |
1986年 | 38篇 |
1985年 | 42篇 |
1984年 | 39篇 |
1983年 | 31篇 |
1982年 | 28篇 |
1981年 | 28篇 |
1980年 | 25篇 |
1979年 | 15篇 |
1978年 | 20篇 |
1977年 | 17篇 |
1976年 | 31篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(45):19718-19731
Metals and alloys forming reversible hydrides with hydrogen gas are potential building blocks for compact, solid state hydrogen storage systems. Based on the materials’ thermodynamic characteristics, their use as temperature-swing gas compression and delivery systems in the hydrogen economy is also possible. Given the wide variety of materials developed and tested at laboratory and pilot scales, a harmonized method of selecting the feasible material(s) for a particular real-life application is required. This study proposes a system selection framework based on a normalized, multi-criteria metric. Using calculated values of multi-criteria metric, multi-criteria screening and ranking of potential materials has been demonstrated for a particular use case. It is found that the alloy TiMn1.52 having value of additive metric between 0.25 and 0.35 represents the best material for a single stage system. The alloy pair CaNi5–Ti1.5CrMn represents the best alternative for a two-stage system with additive metric values between 0.63 and 0.82. Energy and economic characteristics of the metal hydride gas compression and delivery systems are evaluated and compared with an equivalent mechanical compression system producing the same final effect (i.e., delivery of a given quantity of gas at a defined pressure). 相似文献
2.
In the Internet of Things (IoT), a huge amount of valuable data is generated by various IoT applications. As the IoT technologies become more complex, the attack methods are more diversified and can cause serious damages. Thus, establishing a secure IoT network based on user trust evaluation to defend against security threats and ensure the reliability of data source of collected data have become urgent issues, in this paper, a Data Fusion and transfer learning empowered granular Trust Evaluation mechanism (DFTE) is proposed to address the above challenges. Specifically, to meet the granularity demands of trust evaluation, time–space empowered fine/coarse grained trust evaluation models are built utilizing deep transfer learning algorithms based on data fusion. Moreover, to prevent privacy leakage and task sabotage, a dynamic reward and punishment mechanism is developed to encourage honest users by dynamically adjusting the scale of reward or punishment and accurately evaluating users’ trusts. The extensive experiments show that: (i) the proposed DFTE achieves high accuracy of trust evaluation under different granular demands through efficient data fusion; (ii) DFTE performs excellently in participation rate and data reliability. 相似文献
3.
4.
Yuzhu Su Junpu Wang Xin Li Qiqi Tang Jing Yang Li Lei Yi Tian Zhiwei Wang Duanwei He 《Ceramics International》2021,47(15):21077-21082
The in situ axial X-ray diffraction patterns of four ceramic powder samples (MgO, Al2O3, AlN, and cBN) that were compressed in a diamond anvil cell under uniaxial non-hydrostatic conditions were recorded. The microscopic deviatoric stress as a function of the pressure was determined from the X-ray diffraction peak broadening analysis: the curves increased approximately linearly with the pressure at the initial compression stage and then levelled off under further compression. Pressure-induced transparency was observed in all of the samples under compression, and the pressure at the turning point on the curves of the microscopic deviatoric stress versus pressure corresponded to the pressure at which the samples became transparent. Analysis of the microstructural features of the pressure-induced transparent samples indicated that the compression caused the grains to fracture, and the broken grains bonded with each other. We demonstrated that the ceramics’ pressure-induced transparency was a process during which the grains were squeezed and broken, the pores were close between the grains, and the broken grains were re-bonded under compression. 相似文献
5.
6.
Because of heat amount is different from peripheral to central of friction welding interface, which is leaded to vary the characterizations along that interface. Current study, respectively, focused on the effect of different friction pressure on micro-structural and mechanical properties of that friction welding joint interface. Presently, these friction pressures are 110, 130, 150 and 170 MPa while kept all other conditions constant. The effects of different friction pressure on welding interface characterization were investigated by EDX, SEM, tensile, compression, impact and hardness tests. The tensile tests carried out on the standardized test piece with diameter 6 mm and 8 mm, thus, compression tests were extracted from the positions of 0°, 45° 90° with test specimen of 4 mm diameter and 6.5 mm length at weld center. Whereas, the impact test pieces were picked up in two positions, the first one is symmetrical, which it obtained to the respect of the rotation axis and the interface, on the other hand, the second one is non-symmetrical with the axis of rotation and symmetrical to the interface, for making the notch head coincide with the center of the welded joint, The obtained results showed that with reducing of friction pressure will present lack of bonding increasing from peripheral toward the welding center, which will responsible on reducing of the mechanical properties such as tensile, compression and impact strength. 相似文献
7.
目前管道泄漏检测方法可有效检测突发泄漏,对于缓慢泄漏则存在检测灵敏度低、定位不准确等问题。基于此,提出了一种基于信号增强的缓慢泄漏检测方法。通过信号压缩(抽取及移位)克服缓慢泄漏压力信号下降平缓的缺点;根据声波信号具有波形尖锐突出、对突发泄漏敏感的优点,通过建立以压力为输入、虚拟声波为输出的声波信号变送器模型,将压力信号转换为声波信号,克服了泄漏压力信号容易被淹没在管道压力波动及背景噪声中的缺点,实现了缓慢泄漏信号的增强;利用临近插值方法重构虚拟声波信号,基于延时互相关分析实现了缓慢泄漏的准确定位。实验结果表明,该方法具有显著的信号增强效果和定位精度,实现了缓慢泄漏的准确检测。 相似文献
8.
In this paper we combine video compression and modern image processing methods. We construct novel iterative filter methods for prediction signals based on Partial Differential Equation (PDE) based methods. The mathematical framework of the employed diffusion filter class is given and some desirable properties are stated. In particular, two types of diffusion filters are constructed: a uniform diffusion filter using a fixed filter mask and a signal adaptive diffusion filter that incorporates the structures of the underlying prediction signal. The latter has the advantage of not attenuating existing edges while the uniform filter is less complex. The filters are embedded into a software based on HEVC with additional QTBT (Quadtree plus Binary Tree) and MTT (Multi-Type-Tree) block structure. In this setting, several measures to reduce the coding complexity of the tool are introduced, discussed and tested thoroughly. The coding complexity is reduced by up to 70% while maintaining over 80% of the gain. Overall, the diffusion filter method achieves average bitrate savings of 2.27% for Random Access having an average encoder runtime complexity of 119% and 117% decoder runtime complexity. For individual test sequences, results of 7.36% for Random Access are accomplished. 相似文献
9.
An integrated approach to measure the cost efficiency of the postal network of Universal Service Provider is proposed. An integrated approach enables the measurement of cost efficiency for delivery and non-delivery postal network units. The proposed approach is verified and tested on the postal network of the selected provider and the results were derived by using Data Envelopment Analysis (DEA). The results show that the main sources of inefficiency are inadequate allocation of resources relative to the network units. In addition, the study indicates that economies of scale have a positive impact on the efficiency of postal network units. 相似文献
10.