全文获取类型
收费全文 | 142505篇 |
免费 | 14519篇 |
国内免费 | 9322篇 |
专业分类
电工技术 | 10769篇 |
技术理论 | 10篇 |
综合类 | 12989篇 |
化学工业 | 20436篇 |
金属工艺 | 8817篇 |
机械仪表 | 9785篇 |
建筑科学 | 11171篇 |
矿业工程 | 5283篇 |
能源动力 | 3915篇 |
轻工业 | 13496篇 |
水利工程 | 3723篇 |
石油天然气 | 6209篇 |
武器工业 | 1862篇 |
无线电 | 16000篇 |
一般工业技术 | 14270篇 |
冶金工业 | 6182篇 |
原子能技术 | 1895篇 |
自动化技术 | 19534篇 |
出版年
2024年 | 652篇 |
2023年 | 2364篇 |
2022年 | 5066篇 |
2021年 | 6918篇 |
2020年 | 4954篇 |
2019年 | 3546篇 |
2018年 | 3934篇 |
2017年 | 4347篇 |
2016年 | 4047篇 |
2015年 | 6006篇 |
2014年 | 7539篇 |
2013年 | 8857篇 |
2012年 | 10734篇 |
2011年 | 11320篇 |
2010年 | 10170篇 |
2009年 | 9640篇 |
2008年 | 9825篇 |
2007年 | 9453篇 |
2006年 | 8407篇 |
2005年 | 6941篇 |
2004年 | 5069篇 |
2003年 | 3820篇 |
2002年 | 3565篇 |
2001年 | 3186篇 |
2000年 | 3084篇 |
1999年 | 2498篇 |
1998年 | 1822篇 |
1997年 | 1483篇 |
1996年 | 1448篇 |
1995年 | 1189篇 |
1994年 | 1030篇 |
1993年 | 740篇 |
1992年 | 575篇 |
1991年 | 414篇 |
1990年 | 367篇 |
1989年 | 340篇 |
1988年 | 231篇 |
1987年 | 158篇 |
1986年 | 114篇 |
1985年 | 87篇 |
1984年 | 68篇 |
1983年 | 49篇 |
1982年 | 56篇 |
1981年 | 42篇 |
1980年 | 51篇 |
1979年 | 27篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1959年 | 12篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Tao Li Zehui Du Nobumichi Tamura Mao Ye Saikumar Inguva Wei Lu Xierong Zeng Shanming Ke Haitao Huang 《Journal of the European Ceramic Society》2018,38(4):1488-1497
(1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this work, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25 °C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in x = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (TC), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient. 相似文献
52.
Baizhan Li Chenqiu Du Hong Liu Wei Yu Jie Zheng Meilan Tan Zhenxing Jin Wenjie Li Jing Wu Lu Chen Runming Yao 《Indoor air》2019,29(2):308-319
The extensive research interests in environmental temperature can be linked to human productivity / performance as well as comfort and health; while the mechanisms of physiological indices responding to temperature variations remain incompletely understood. This study adopted a physiological sensory nerve conduction velocity (SCV) as a temperature‐sensitive biomarker to explore the thermoregulatory mechanisms of human responding to annual temperatures. The measurements of subjects’ SCV (over 600 samples) were conducted in a naturally ventilated environment over all four seasons. The results showed a positive correlation between SCV and annual temperatures and a Boltzmann model was adopted to depict the S‐shaped trend of SCV with operative temperatures from 5°C to 40°C. The SCV increased linearly with operative temperatures from 14.28°C to 20.5°C and responded sensitively for 10.19°C‐24.59°C, while tended to be stable beyond that. The subjects’ thermal sensations were linearly related to SCV, elaborating the relation between human physiological regulations and subjective thermal perception variations. The findings reveal the body SCV regulatory characteristics in different operative temperature intervals, thereby giving a deeper insight into human autonomic thermoregulation and benefiting for built environment designs, meantime minimizing the temperature‐invoked risks to human health and well‐being. 相似文献
53.
We propose an analytical model to evaluate the lightpath blocking performance for a single ROADM node with intra-node add/drop contention,in which the number of lightpaths that can be added/dropped with the same wavelength is limited by the add/drop contention factor.Different models of traffic load per nodal degree are considered to validate the effectiveness of the analytical model.The simulation results show that the proposed analytical model is effective in predicting the performance for different values of add/drop contention factor C and for variable offered loads at the node.The add/drop contention factor shows an important impact on the lightpath blocking performance and properly raising the contention factor can significantly improve the lightpath blocking performance.When the add/drop contention factor C exceeds a certain level,the performance of a ROADM with intra-node contention is close to that of a contentionless ROADM. 相似文献
54.
55.
56.
57.
58.
59.
Haitang Yang Zilong Lu Bixiong Bie Zeyu Fu Jianling Yue Xiaozhong Huang 《Ceramics International》2019,45(9):11395-11402
SiCf/PyC/SiC and SiCf/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiCf/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiCf/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiCf/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B2O3 molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B2O3, the SiCf/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO2 grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiCf/PyC/SiC and SiCf/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale. 相似文献
60.
In the early design stage, automotive modeling should both meet the requirements of aesthetics and engineering. Therefore, a vehicle CAD (computer aided design) model that can be easily adjusted by feedbacks is necessary. Based on CE-Bézier surface, this paper presents a set of algorithms for parametric segmentation and fairing surface generation in a car model. This model is defined by a simplified automotive template and relevant control points, shape parameters and segmentation parameters, which can be modified to alter the car form efficiently. With this model and the corresponding adjustment method, more than fifty various vehicle models are established in this research according to different parameters. And two methods for calculating similarity index between car models are constructed, which are suitable for brand design trend analysis and modelling design decisionmaking. 相似文献