全文获取类型
收费全文 | 67309篇 |
免费 | 4440篇 |
国内免费 | 2802篇 |
专业分类
电工技术 | 2852篇 |
技术理论 | 3篇 |
综合类 | 3135篇 |
化学工业 | 9989篇 |
金属工艺 | 4433篇 |
机械仪表 | 3782篇 |
建筑科学 | 4041篇 |
矿业工程 | 1248篇 |
能源动力 | 2247篇 |
轻工业 | 3592篇 |
水利工程 | 922篇 |
石油天然气 | 3429篇 |
武器工业 | 349篇 |
无线电 | 7882篇 |
一般工业技术 | 11972篇 |
冶金工业 | 5820篇 |
原子能技术 | 857篇 |
自动化技术 | 7998篇 |
出版年
2024年 | 189篇 |
2023年 | 729篇 |
2022年 | 1299篇 |
2021年 | 1835篇 |
2020年 | 1396篇 |
2019年 | 1371篇 |
2018年 | 1618篇 |
2017年 | 1788篇 |
2016年 | 1709篇 |
2015年 | 1912篇 |
2014年 | 2617篇 |
2013年 | 3956篇 |
2012年 | 3416篇 |
2011年 | 4203篇 |
2010年 | 3521篇 |
2009年 | 3599篇 |
2008年 | 3633篇 |
2007年 | 3511篇 |
2006年 | 3493篇 |
2005年 | 3002篇 |
2004年 | 2285篇 |
2003年 | 2439篇 |
2002年 | 2655篇 |
2001年 | 2391篇 |
2000年 | 2009篇 |
1999年 | 2121篇 |
1998年 | 2462篇 |
1997年 | 1896篇 |
1996年 | 1754篇 |
1995年 | 1230篇 |
1994年 | 1027篇 |
1993年 | 811篇 |
1992年 | 546篇 |
1991年 | 467篇 |
1990年 | 330篇 |
1989年 | 323篇 |
1988年 | 276篇 |
1987年 | 179篇 |
1986年 | 113篇 |
1985年 | 96篇 |
1984年 | 62篇 |
1983年 | 49篇 |
1982年 | 48篇 |
1981年 | 43篇 |
1980年 | 26篇 |
1979年 | 18篇 |
1977年 | 8篇 |
1976年 | 20篇 |
1975年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
通过对普查区喜山期玄武岩喷发分布范围、形态的分析,对燕山晚期闪长玢岩分布范围、与构造关系、对煤层的影响等方面的分析,阐述了太平普查区岩浆活动特征。 相似文献
32.
Strength of Materials - A metallographic method, dilatometry, and X-ray diffraction were applied to investigate the effects of undercooling and holding time on bainitic transformation,... 相似文献
33.
Journal of Porous Materials - In this work, a trifluoromethanesulfonic acid (TFOH) modified clay (TFOH-Clay) was developed for the removal of trace olefins in heavy naphtha. 5%TFOH-Clay can... 相似文献
34.
This paper presents a spatio-temporal fusion method for remote sensing images by using a linear injection model and local neighbourhood information. In this method, the linear injection model is first introduced to generate an initial fused image, the spatial details are extracted from the fine-resolution image at the base date, and are weighted by a proper injection gains. Then, the spatial details and the relative spectral information from the coarse-resolution images are blended to generate the fusion result. To further enhance its robustness to the noise, the local neighbourhood information, derived from the fine-resolution image and the fused result simultaneously, is introduced to refine the initial fused image to obtain a more accurate prediction result. The algorithm can effectively capture phenology change or land-cover-type change with minimum input data. Simulated data and two types of real satellite images with seasonal changes and land-cover-type changes are employed to test the performance of the proposed method. Compared with a spatial and temporal adaptive reflectance fusion model (STARFM) and a flexible spatio-temporal fusion algorithm (FSDAF), results show that the proposed approach improves the accuracy of fused images in phenology change area and effectively captures land-cover-type reflectance changes. 相似文献
35.
Xiaopo Wu Yangming Shi Weibo Meng Xiaofei Ma Nian Fang 《International Journal of Satellite Communications and Networking》2019,37(3):283-291
Electromagnetic signal emitted by satellite communication (satcom) transmitters are used to identify specific individual uplink satcom terminals sharing the common transponder in real environment, which is known as specific emitter identification (SEI) that allows for early indications and warning (I&W) of the targets carrying satcom furnishment and furthermore the real time electromagnetic situation awareness in military operations. In this paper, the authors are the first to propose the identification of specific transmitters of satcom by using probabilistic neural networks (PNN) to reach the goal of target recognition. We have been devoted to the examination by exploring the feasibility of utilizing the Hilbert transform to signal preprocessing, applying the discrete wavelet transform to feature extraction, and employing the PNN to perform the classification of stationary signals. There are a total of 1000 sampling time series with binary phase shift keying (BPSK) modulation originated by five types of satcom transmitters in the test. The established PNNs classifier implements the data testing and finally yields satisfactory accuracy at 8 dB(±1 dB) carrier to noise ratio, which indicates the feasibility of our method, and even the keen insight of its application in military. 相似文献
36.
Crystallographic characteristics and microwave dielectric properties of Ni-modified MgTa2O6 ceramics
Liang Shi Xueying Wang Rui Peng Gang Wang Cheng Liu Xiaolei Shi Dainan Zhang Huaiwu Zhang 《Ceramics International》2021,47(16):22514-22521
Ni2+ modified MgTa2O6 ceramics with a trirutile phase and space group P42/mnm were obtained. The correlations between crystallographic characteristics and microwave dielectric performance of MgTa2O6 ceramics were systematically studied based on the chemistry bond theory (PVL theory) for the first time. The results indicate that the introduction of Ni2+ causes a change in polarizability and the Mg–O bond ionicity, which contributes to the variation of dielectric constant. Moreover, the lattice energy, and packing fraction, full width at half maximum of the Raman peak of Ta–O bond, as the quantitative characterization of crystallographic parameters, regulate the dielectric loss of MgTa2O6 ceramics in GHz frequency band. In addition, the study of sintering behavior shows that the densification and micromorphology are the crucial factors affecting the microwave dielectric performance. Typically, Ni2+ doping on the A-site of MgTa2O6 can effectively promote the Q × f values to 173,000 GHz (at 7.43 GHz), which ensures its applicability in 5G communication technology. 相似文献
37.
Liang Shi Dainan Zhang Rui Peng Cheng Liu Xiaolei Shi Xueying Wang Huaiwu Zhang 《Journal of the European Ceramic Society》2021,41(11):5526-5530
Mg(1-x)ZnxTa2O6 (x = 0.00?0.08) dielectric ceramics were synthesized via the traditional solid-state reaction method. We used XRD and Rietveld refinement to demonstrate that a pure Mg(1-x)ZnxTa2O6 phase with trirutile structure was formed. Zn2+ substitution helped to decrease the Raman full width at half width of the A1g mode at 703 cm?1, which resulted in an increase in the order and rigidity of the TaO6 octahedron, this in turn contributed to improving the Q×f values. Additionally, the introduction of Zn2+ significantly promoted grain growth and increased the dense, and the molecular polarizability, these factors lead to a higher permittivity. Moreover, enhanced Ta-O bond energy resulted in a more stable TaO6 octahedron in the Mg(1?x)ZnxTa2O6 system, which contributed to enhanced τf values via substitution of Zn2+ doped on the A-site. Correspondingly, the microwave dielectric properties were significantly improved for 0.04-doped samples, obtaining: εr = 27, Q × f = 185,000 GHz (at 7.47 GHz), τf =32 ppm/°C. 相似文献
38.
39.
Neural Computing and Applications - Traffic identification is currently an important challenge for network management and security. In this paper, we propose a novel application identification... 相似文献
40.
Sophia X. Sui Lana J. Williams Kara L. Holloway-Kew Natalie K. Hyde Julie A. Pasco 《International journal of molecular sciences》2021,22(1)
Sarcopenia is the loss of skeletal muscle mass and function with advancing age. It involves both complex genetic and modifiable risk factors, such as lack of exercise, malnutrition and reduced neurological drive. Cognitive decline refers to diminished or impaired mental and/or intellectual functioning. Contracting skeletal muscle is a major source of neurotrophic factors, including brain-derived neurotrophic factor, which regulate synapses in the brain. Furthermore, skeletal muscle activity has important immune and redox effects that modify brain function and reduce muscle catabolism. The identification of common risk factors and underlying mechanisms for sarcopenia and cognition may allow the development of targeted interventions that slow or reverse sarcopenia and also certain forms of cognitive decline. However, the links between cognition and skeletal muscle have not been elucidated fully. This review provides a critical appraisal of the literature on the relationship between skeletal muscle health and cognition. The literature suggests that sarcopenia and cognitive decline share pathophysiological pathways. Ageing plays a role in both skeletal muscle deterioration and cognitive decline. Furthermore, lifestyle risk factors, such as physical inactivity, poor diet and smoking, are common to both disorders, so their potential role in the muscle–brain relationship warrants investigation. 相似文献