全文获取类型
收费全文 | 231068篇 |
免费 | 30308篇 |
国内免费 | 25583篇 |
专业分类
电工技术 | 20926篇 |
技术理论 | 10篇 |
综合类 | 17419篇 |
化学工业 | 41591篇 |
金属工艺 | 10319篇 |
机械仪表 | 15609篇 |
建筑科学 | 9852篇 |
矿业工程 | 3790篇 |
能源动力 | 6509篇 |
轻工业 | 19067篇 |
水利工程 | 2974篇 |
石油天然气 | 5795篇 |
武器工业 | 2903篇 |
无线电 | 35092篇 |
一般工业技术 | 24227篇 |
冶金工业 | 6097篇 |
原子能技术 | 3654篇 |
自动化技术 | 61125篇 |
出版年
2024年 | 560篇 |
2023年 | 3596篇 |
2022年 | 6024篇 |
2021年 | 8256篇 |
2020年 | 7907篇 |
2019年 | 6941篇 |
2018年 | 6429篇 |
2017年 | 8843篇 |
2016年 | 9765篇 |
2015年 | 11406篇 |
2014年 | 12015篇 |
2013年 | 15130篇 |
2012年 | 17655篇 |
2011年 | 19857篇 |
2010年 | 14257篇 |
2009年 | 14140篇 |
2008年 | 15423篇 |
2007年 | 17340篇 |
2006年 | 16440篇 |
2005年 | 14178篇 |
2004年 | 11985篇 |
2003年 | 9597篇 |
2002年 | 7317篇 |
2001年 | 5538篇 |
2000年 | 4502篇 |
1999年 | 3650篇 |
1998年 | 3050篇 |
1997年 | 2493篇 |
1996年 | 2173篇 |
1995年 | 1859篇 |
1994年 | 1673篇 |
1993年 | 1298篇 |
1992年 | 1033篇 |
1991年 | 820篇 |
1990年 | 717篇 |
1989年 | 563篇 |
1988年 | 421篇 |
1987年 | 252篇 |
1986年 | 235篇 |
1985年 | 324篇 |
1984年 | 271篇 |
1983年 | 222篇 |
1982年 | 253篇 |
1981年 | 134篇 |
1980年 | 127篇 |
1979年 | 58篇 |
1978年 | 34篇 |
1977年 | 47篇 |
1976年 | 26篇 |
1959年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
According to the circle-packing theorem, the packing efficiency of a hexagonal lattice is higher than an equivalent square tessellation. Consequently, in several contexts, hexagonally sampled images compared to their Cartesian counterparts are better at preserving information content. In this paper, novel mapping techniques alongside the wavelet compression scheme are presented for hexagonal images. Specifically, we introduce two tree-based coding schemes, referred to as SBHex (spirally-mapped branch-coding for hexagonal images) and BBHex (breadth-first block-coding for hexagonal images). Both of these coding schemes respect the geometry of the hexagonal lattice and yield better compression results. Our empirical results show that the proposed algorithms for hexagonal images produce better reconstruction quality at low bits per pixel representations compared to the tree-based coding counterparts for the Cartesian grid. 相似文献
32.
《Ceramics International》2021,47(18):25863-25874
The inherent brittleness of bioceramics restricts their applications in load-bearing implant, although they possess good biocompatibility and bioactivity. ZnO, MgO and 58S bioglass (BG) were incorporated as additives to further improve the mechanical properties and biocompatibility of β-TCP and ZnO/MgO/BG-β-TCP composite scaffolds were manufactured via digital light processing (DLP). The composite with the best comprehensive performance was selected for degradation behavior and biocompatibility evaluation. The effects of different proportions of ZnO/MgO/BG on mechanical strength were analyzed and ZnO0·5/MgO1/BG2-β-TCP (ZMBT) samples exhibited superior mechanical strength. The improvement by 272% and 99% respectively was achieved in fracture toughness and compressive strength with the optimal recipe. The enhancement effect is realized through phase transition, alterative sliding actions and transgranular fracture to effectively prevent the load transfer combining the functions of bioglass and metal oxide. ZMBT scaffolds exhibited a more desirable pH environment and an enhanced ability of apatite-mineralization formation, meanwhile Si4+, Mg2+ and Zn2+ were gradually released from scaffolds. Furthermore, in vitro evaluation indicated that ZMBT scaffolds presented not only excellent cell attachment, proliferation, alkaline phosphatase (ALP) activity, but they up-regulated osteogenic gene (ALP, OCN, Runx2). These results suggest that the addition of ZnO/MgO/BG to DLP-printed β-TCP scaffolds offer a smart strategy to fabricate porous scaffolds with conspicuously better biological and physicochemical properties including compressive strength, bioactivity, osteogenesis and osteogenesis-related gene expression. Metal-oxide and BG synergistically enhanced the mechanical and biological properties which make the ZMBT scaffolds a strong candidate for bone repair applications. 相似文献
33.
Mit Rita Goswami Prayas Singh Pankaj Chamoli Sumit Bhardwaj Kuldeep Kumar Raina Ravi Kumar Shukla 《应用聚合物科学杂志》2021,138(43):51260
ZnO rice like nonarchitects are grafted on the graphene carbon core via a rapid microwave synthesis route. The prepared grafted systems are characterized via XRD, SEM, RAMAN, and XPS to examined the structural and morphological parameters. Zinc oxide grafted graphene sheets (ZnO-G) are further doped in β-phase of polyvinylidene fluoride (PVDF) to prepare the polymer nanocomposites (PNCs) via mixed solvent approach (THF/DMF). β-phase confirmation of PVDF PNCs is done by FTIR studies. It is observed that ZnO-G filler enhances the β-phase content in the PNCs. Non-doped PVDF and PNCs are further studied for rheological behavior under the shear rate of 1–100 s−1. Doping of ZnO-G dopant to the PVDF matrix changes its discontinuous shear thickening (DST) behavior to continues shear thickening behavior (CST). Hydrocluster formation and their interaction with the dopant could be the reason for this striking DST to CST behavioral change. Strain amplitude sweep (10−3% -10%) oscillatory test reveals that the PNCs shows extended linear viscoelastic region with high elastic modulus and lower viscous modulus. Effective shear thickening behavior and strong elastic strength of these PNCs present their candidature for various fields including mechanical and soft body armor applications. 相似文献
34.
During the service life of structural sealant glazing (SSG) facades, the load-bearing capacity of the silicone bonds needs to be guaranteed. Laboratory tests can assess the durability of SSG-systems based on mechanical characteristics of the bond after simultaneous exposure to both climatic and mechanical loads. This article studies how the material characteristics of two common structural sealants are affected by laboratory and field exposure. Dynamic mechanical analysis (DMA) confirms a reduction in the dynamic modulus of exposed silicone samples. Results from thermogravimetric analysis, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering/wide-angle X-ray scattering show differences between the two sealants and indicate no/minor changes in the composition and morphology of the laboratory and field exposed sealants. Mechanical characterization methods, such as DMA, and tensile and shear testing of the structural bond, are shown to be sensitive toward the combined climatic and mechanical loadings, and are hence suitable for studying degradation mechanisms of structural sealants. 相似文献
35.
Paulina Koodziej-Wojnar Joanna Borkowska Zofia Wicik Anna Domaszewska-Szostek Jacek Poosak Marta Ckaa-Jakimowicz Olga Bujanowska Monika Puzianowska-Kuznicka 《International journal of molecular sciences》2021,22(1)
5-Hydroxymethylcytosine (5hmC) is a functionally active epigenetic modification. We analyzed whether changes in DNA 5-hydroxymethylation are an element of age-related epigenetic drift. We tested primary fibroblast cultures originating from individuals aged 22–35 years and 74–94 years. Global quantities of methylation-related DNA modifications were estimated by the dot blot and colorimetric methods. Regions of the genome differentially hydroxymethylated with age (DHMRs) were identified by hMeDIP-seq and the MEDIPS and DiffBind algorithms. Global levels of DNA modifications were not associated with age. We identified numerous DHMRs that were enriched within introns and intergenic regions and most commonly associated with the H3K4me1 histone mark, promoter-flanking regions, and CCCTC-binding factor (CTCF) binding sites. However, only seven DHMRs were identified by both algorithms and all of their settings. Among them, hypo-hydroxymethylated DHMR in the intron of Rab Escort Protein 1 (CHM) coexisted with increased expression in old cells, while increased 5-hydroxymethylation in the bodies of Arginine and Serine Rich Protein 1 (RSRP1) and Mitochondrial Poly(A) Polymerase (MTPAP) did not change their expression. These age-related differences were not associated with changes in the expression of any of the ten-eleven translocation (TET) enzymes or their activity. In conclusion, the distribution of 5hmC in DNA of in vivo aged human fibroblasts underwent age-associated modifications. The identified DHMRs are, likely, marker changes. 相似文献
36.
Anna Masek Stefan Cichosz Magorzata Piotrowska 《International journal of molecular sciences》2021,22(6)
The study aimed to prepare sustainable and degradable elastic blends of epoxidized natural rubber (ENR) with poly(lactic acid) (PLA) that were reinforced with flax fiber (FF) and montmorillonite (MMT), simultaneously filling the gap in the literature regarding the PLA-containing polymer blends filled with natural additives. The performed study reveals that FF incorporation into ENR/PLA blend may cause a significant improvement in tensile strength from (10 ± 1) MPa for the reference material to (19 ± 2) MPa for the fibers-filled blend. Additionally, it was found that MMT employment in the role of the filler might contribute to ENR/PLA plasticization and considerably promote the blend elongation up to 600%. This proves the successful creation of the unique and eco-friendly PLA-containing polymer blend exhibiting high elasticity. Moreover, thanks to the performed accelerated thermo-oxidative and ultraviolet (UV) aging, it was established that MMT incorporation may delay the degradation of ENR/PLA blends under the abovementioned conditions. Additionally, mold tests revealed that plant-derived fiber addition might highly enhance the ENR/PLA blend’s biodeterioration potential enabling faster and more efficient growth of microorganisms. Therefore, materials presented in this research may become competitive and eco-friendly alternatives to commonly utilized petro-based polymeric products. 相似文献
37.
Shi-yuan XU Chu-ming LIU Ying-chun WAN Guang ZENG Yong-hao GAO Shu-nong JIANG 《中国有色金属学会会刊》2021,31(5):1291-1302
The corrosion behaviour of Mg-6Gd-3Y-1Zn-0.3Ag (wt.%) alloy components with different sizes after cooling was investigated. The alloys in the small components (SC) cooled fast, which were composed of α-Mg matrix and coarse long-period stacking ordered (LPSO) phases. The alloys in the large components (LC) cooled slowly, and there were thin lamellar LPSO phases precipitating inside the grains, except for α-Mg matrix and coarse LPSO phases. The hydrogen evolution test revealed that the corrosion rate of LC sample was higher than that of SC sample. Electrochemical impedance spectroscopy (EIS) test showed that the surface film on LC alloys provided worse protection. The corrosion morphologies indicated that the precipitation of the thin lamellar LPSO phases in LC sample caused severe micro-galvanic corrosion, which accelerated the rupture of the surface film. 相似文献
38.
《International Journal of Hydrogen Energy》2022,47(9):6078-6088
The widespread use of fuel cell technology is hampered by the use of expensive and scarce platinum metal in electrodes which is required to facilitate the sluggish oxygen reduction reaction (ORR). In this work, a viable synthetic approach was developed to prepare iron-based sulfur and nitrogen dual doped porous carbon (Fe@SNDC) for use in ORR. Benzimidazole, a commercially available monomer, was used as a precursor for N doped carbon and calcined with potassium thiocyanate at different temperatures to tune the pore size, nitrogen content and different types of nitrogen functionality such as pyridinic, pyrrolic and graphitic. The Fe@SNDC–950 with high surface area, optimum N content of about 5 at% and high amount of pyridinic and graphitic N displayed an onset potential and half-wave potential of 0.98 and 0.83 V vs RHE, respectively, in 0.1 M KOH solution. The catalyst also exhibits similar oxygen reduction reaction performance compared to Pt/C (20 wt%) in acidic media. Furthermore, when compared to commercially available Pt/C (20 wt%), Fe@SNDC–950 showed enhanced durability over 6 h and poison tolerance in case of methanol crossover with the concentration up to 3.0 M in oxygen saturated alkaline electrolyte. Our study demonstrates that the presence of N and S along with Fe-N moieties synergistically served as ORR active sites while the high surface area with accessible pores allowed for efficient mass transfer and interaction of oxygen molecules to the active sites contributing to the ORR activity of the catalyst. 相似文献
39.
三维异质异构集成技术是实现电子信息系统向着微型化、高效能、高整合、低功耗及低成本方向发展的最重要方法,也是决定信息化平台中微电子和微纳系统领域未来发展的一项核心高技术。文章详细介绍了毫米波频段三维异质异构集成技术的优势、近年来的发展趋势以及面临的挑战。利用硅基MEMS 光敏复合薄膜多层布线工艺可实现异质芯片的低损耗互连,同时三维集成高性能封装滤波器、高辐射效率封装天线等无源元件,还能很好地处理布线间的电磁兼容和芯片间的屏蔽问题。最后介绍了一款新型毫米波三维异质异构集成雷达及其在远距离生命体征探测方面的应用。 相似文献
40.