全文获取类型
收费全文 | 81879篇 |
免费 | 9450篇 |
国内免费 | 5856篇 |
专业分类
电工技术 | 7149篇 |
技术理论 | 3篇 |
综合类 | 10921篇 |
化学工业 | 6842篇 |
金属工艺 | 4492篇 |
机械仪表 | 7499篇 |
建筑科学 | 10399篇 |
矿业工程 | 3374篇 |
能源动力 | 2533篇 |
轻工业 | 2511篇 |
水利工程 | 3043篇 |
石油天然气 | 2862篇 |
武器工业 | 1090篇 |
无线电 | 6676篇 |
一般工业技术 | 11027篇 |
冶金工业 | 2779篇 |
原子能技术 | 747篇 |
自动化技术 | 13238篇 |
出版年
2024年 | 139篇 |
2023年 | 1002篇 |
2022年 | 1581篇 |
2021年 | 1980篇 |
2020年 | 2391篇 |
2019年 | 2281篇 |
2018年 | 2102篇 |
2017年 | 2692篇 |
2016年 | 2997篇 |
2015年 | 3204篇 |
2014年 | 4884篇 |
2013年 | 5062篇 |
2012年 | 6039篇 |
2011年 | 6459篇 |
2010年 | 4832篇 |
2009年 | 5230篇 |
2008年 | 4964篇 |
2007年 | 5964篇 |
2006年 | 5393篇 |
2005年 | 4471篇 |
2004年 | 3753篇 |
2003年 | 3268篇 |
2002年 | 2722篇 |
2001年 | 2299篇 |
2000年 | 1936篇 |
1999年 | 1648篇 |
1998年 | 1200篇 |
1997年 | 1165篇 |
1996年 | 972篇 |
1995年 | 905篇 |
1994年 | 762篇 |
1993年 | 595篇 |
1992年 | 492篇 |
1991年 | 345篇 |
1990年 | 320篇 |
1989年 | 240篇 |
1988年 | 199篇 |
1987年 | 137篇 |
1986年 | 88篇 |
1985年 | 54篇 |
1984年 | 77篇 |
1983年 | 56篇 |
1982年 | 48篇 |
1981年 | 39篇 |
1980年 | 42篇 |
1979年 | 37篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1975年 | 8篇 |
1959年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Aiming at the performance degradation of the existing presentation attack detection methods due to the illumination variation, a two-stream vision transformers framework (TSViT) based on transfer learning in two complementary spaces is proposed in this paper. The face images of RGB color space and multi-scale retinex with color restoration (MSRCR) space are fed to TSViT to learn the distinguishing features of presentation attack detection. To effectively fuse features from two sources (RGB color space images and MSRCR images), a feature fusion method based on self-attention is built, which can effectively capture the complementarity of two features. Experiments and analysis on Oulu-NPU, CASIA-MFSD, and Replay-Attack databases show that it outperforms most existing methods in intra-database testing and achieves good generalization performance in cross-database testing. 相似文献
4.
《Ceramics International》2022,48(8):10579-10591
In present study, we report a V doping fabrication method for obtaining rod-like MgO crystals decorated with a nanoflake layer. This novel structure has only been minimally reported in literature. Pure MgO and Mg2V2O7–MgO composite materials were obtained by precipitation and impregnation methods, with vanadium added concentrations of 0–9%. The influence of V doping on crystal structure and particle morphology of MgO was investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis demonstrated that MgO has a cubic structure, while X-ray photoelectron spectroscopy (XPS) revealed that V5+ exists on the surface of MgO. The specific surface areas and pore sizes of MgO composites were calculated by BET and BJH analysis. These techniques revealed that specific surface area and pore size of MgO increased due to vanadium doping. The antibacterial effects of Mg2V2O7–MgO composite materials against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were assessed using a bacterial killing/colony-forming unit (CFU) assay and bacteriostatic ring method. Our results demonstrate that V doping dramatically improved antimicrobial properties of MgO, with 7 mol% doping inducing the best antibacterial activity. The antibacterial mechanisms of Mg2V2O7–MgO composite material were also proposed. 相似文献
5.
《International Journal of Hydrogen Energy》2022,47(64):27508-27515
Customizing catalysts from the electronic structure, such as spin state, is an effective but challenging strategy for oxygen evolution reaction (OER). Herein, an ultrafine Co–Fe material highly dispersed on nitrogen carbide matrix is fabricated by coordination polymer and self-templating method to scrutinize the impact of spin state of Co on OER through Fe doping. The optimized catalyst shows boosted OER performance, which only requires overpotential of 333 mV at 10 mA cm?2, outperforming other control samples and commercial RuO2. The elevated local spin states of Co by Fe doping lead to charge transfer acceleration and fast generation of oxygenated intermediates, which is proved to account for the OER elevation. In addition, the long-term stability of Co–Fe material is guaranteed by the strong coordination of Co/Fe to the melamine-formaldehyde resin, which is used to adsorb metal ions, contributing to the high dispersion of active sites during the OER process. 相似文献
6.
《International Journal of Hydrogen Energy》2022,47(64):27481-27492
Photocatalytic water splitting has become a promising technology to solve environmental pollution and energy shortage. Exploring stable and efficient photocatalysts are highly desired. Herein, we propose novel low-dimensional InSbS3 semiconductors with good stability based on density functional theory. Such InSbS3 structures could be obtained from their bulk crystal by suitable exfoliation methods. Our calculations indicate that two-dimensional (2D) and one-dimensional (1D) InSbS3 nanostructures have moderate band gaps (2.54 and 1.97 eV, respectively) and suitable band edge alignments, which represents sufficient redox capacity for photocatalytic water splitting. 2D InSbS3 monolayer possesses oxygen evolution reaction (OER) activity and 1D InSbS3 single-nanochain possesses hydrogen evolution reaction (HER) activity under acidic conditions. Interestingly, two edge electron states can be introduced when the dimension of InSbS3 is reduced from 2D to 1D and the new electron states can exist in arbitrary-width nanoribbons, which can effectively promote the process of HER. Moreover, InSbS3 monolayer and single-nanochain also exhibit large solar-to-hydrogen efficiency, high carrier mobility, and excellent optical absorption properties, which can facilitate the process of photocatalytic reactions. Our findings can stimulate the synthesis and applications of low-dimensional InSbS3 semiconductors for overall water splitting. 相似文献
7.
《Soils and Foundations》2022,62(3):101156
In this paper, a newly developed 3-dimentional discrete element model (DEM) for gravel-rubber mixtures (GRMs), namely DEM4GRM, that is capable of accurately describing the macro-scale shear response (from small to large deformation) of GRMs in a direct shear box apparatus is presented. Rigid gravel grains are modelled as simple multi-shape clumps, while soft rubber particles are modeled by using deformable 35-ball body-centered-cubic clusters. Mixtures are prepared with different volumetric rubber content (VRC) at 0, 10, 25, 40 and 100%, statically compressed under 30, 60 and 100 kPa vertical stress and then sheared, by closely simulating a reference laboratory test procedure. The variation of micro-scale factors such as fabric, normal and tangential force anisotropy is carefully examined throughout the shearing process and described by means of novel micro-mechanical relationships valid for GRMs. Moreover, strong-force chains are scrutinized to identify the transition from rigid to soft granular skeleton and gain insights on the load transfer and deformation mechanisms of GRMs. It is shown that the development of the fabric and force anisotropy during shearing is closely related to the macro-scale shear strength of GRMs, and strongly depends on the VRC. Besides, strong-force chains appear to be primarily formed by gravel-gravel contacts (resulting in a rigid-like mechanical behavior) up to VRC = 30%, and by rubber-rubber contacts (causing a soft-like mechanical response) beyond VRC = 60%. Alternatively, at 30% < VRC < 60%, gravel-rubber contacts are predominant in the strong-force network and an intermediate mechanical behavior is observed. This is consistent with the behavioral trends observed in the macro- and micro-mechanical responses. 相似文献
8.
《International Journal of Hydrogen Energy》2022,47(10):6494-6507
The Markov model and the PEM electrolyzer system model for directly coupled photovoltaic are combined to construct an efficient and reliable working condition that fits the fluctuation characteristics of solar energy. The working condition is designed through genetic algorithm so that the average coupling efficiency of the system can reach 98.8%. Then, the durability and recovery test are conducted on the basis of the constructed conditions. It is found that the attenuation rate at the current density of 1A/cm2 under the photovoltaic fluctuating condition reached 7.8mV/h, which is twice that under the constant current condition. The charge transfer impedance (Rct) is the main factor leading to the degradation. It is proved by the recovery experiment that the increase of Rct is related to the pollution of metal ions. After pickling to remove some metal ions, Rct can be significantly reduced by 46.8% and 65.2%, respectively. After the durability test, the voltammetric charges under the photovoltaic fluctuating condition and the constant current condition are reduced by 48.3% and 19.1% It indicates that the photovoltaic fluctuation condition will accelerate the attenuation of the effective reaction area of MEA, which is irreversible even after pickling. It can be observed from the SEM images that the catalyst layer of MEA has more obvious peeling under the photovoltaic fluctuation condition, which is not conducive to material transmission and destroys the transmission channel of ions and electrons. This result can provide a reliable reference for the coupling design of PEM electrolyzer and renewable energy in the future. 相似文献
10.