全文获取类型
收费全文 | 137019篇 |
免费 | 14973篇 |
国内免费 | 7155篇 |
专业分类
电工技术 | 6589篇 |
技术理论 | 2篇 |
综合类 | 9710篇 |
化学工业 | 34064篇 |
金属工艺 | 17692篇 |
机械仪表 | 7061篇 |
建筑科学 | 9239篇 |
矿业工程 | 5600篇 |
能源动力 | 3325篇 |
轻工业 | 13333篇 |
水利工程 | 2607篇 |
石油天然气 | 4535篇 |
武器工业 | 1038篇 |
无线电 | 5844篇 |
一般工业技术 | 26573篇 |
冶金工业 | 7442篇 |
原子能技术 | 1083篇 |
自动化技术 | 3410篇 |
出版年
2024年 | 738篇 |
2023年 | 2674篇 |
2022年 | 4919篇 |
2021年 | 5860篇 |
2020年 | 5271篇 |
2019年 | 4536篇 |
2018年 | 4815篇 |
2017年 | 5623篇 |
2016年 | 5848篇 |
2015年 | 6053篇 |
2014年 | 7735篇 |
2013年 | 9169篇 |
2012年 | 8912篇 |
2011年 | 10440篇 |
2010年 | 7310篇 |
2009年 | 7855篇 |
2008年 | 6855篇 |
2007年 | 7940篇 |
2006年 | 7365篇 |
2005年 | 6088篇 |
2004年 | 5498篇 |
2003年 | 4779篇 |
2002年 | 3971篇 |
2001年 | 3038篇 |
2000年 | 2747篇 |
1999年 | 2196篇 |
1998年 | 1869篇 |
1997年 | 1673篇 |
1996年 | 1335篇 |
1995年 | 1114篇 |
1994年 | 915篇 |
1993年 | 692篇 |
1992年 | 640篇 |
1991年 | 473篇 |
1990年 | 470篇 |
1989年 | 469篇 |
1988年 | 233篇 |
1987年 | 166篇 |
1986年 | 131篇 |
1985年 | 132篇 |
1984年 | 148篇 |
1983年 | 80篇 |
1982年 | 122篇 |
1981年 | 28篇 |
1980年 | 60篇 |
1979年 | 33篇 |
1978年 | 11篇 |
1964年 | 14篇 |
1959年 | 11篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
141.
Jialin Sun Jun Zhao Xiuying Ni Feng Gong Zuoli Li 《Journal of the European Ceramic Society》2018,38(9):3096-3103
This work investigates the critical roles of two-step sintering (TSS) and laminated structure on the sintering behavior and mechanical properties of functionally graded WC-TiC-Al2O3 nanostructured composite materials doped with Cr3C2/VC. Results show that excellent mechanical properties are achieved for tailored TSS conditions with a hardness of 27.91?±?2.3?GPa and a flexural strength of 1423.3?±?23.5?MPa. The desirable mechanical properties are attributed to the suppressed grain growth without densification deterioration. TSS is more effective in facilitating the favorable dispersion of secondary phase toughening nano-particulates in a WC matrix than conventional sintering (CS). Cr3C2/VC dopant plays an important role in maximizing and shifting the temperature range of the kinetic window for WC-Al2O3 composites. Al2O3 crack deflection, transgranular Al2O3, microcracking, WC crack bridging and plate-like WC crack deflection are the major toughening mechanisms. Residual surface compressive stress induced by the graded structure is also an appreciated contribution to the improvement of mechanical properties. 相似文献
142.
《Journal of the European Ceramic Society》2020,40(8):3035-3041
BaCu2-xCoxSi2O7 solid solutions with orthorhombic structure (Pnma) were prepared by solid-state reaction method. The phase synthesis process, structural evolution and microwave dielectric properties of BaCu2-xCoxSi2O7 ceramics were investigated. Single BaCu2Si2O7 phase was obtained when calcined at 950 °C for 3 h and was decomposed into BaCuSi2O6 phase when calcined at 1075 °C for 3 h. The sintering process was effectively promoted when Cu2+ was replaced by Co2+ and the maximum solubility of BaCu2-xCoxSi2O7 was located between 0.15 and 0.20. P-V-L complex chemical bond theory and Raman spectra were used to explain the structure-property correlations of BaCu2-xCoxSi2O7 ceramics. The corrected dielectric constant (εr-corr) of BaCu2-xCoxSi2O7 ceramics decreased monotonously with the susceptibility (Σχμ) and ionic polarizability of primitive unit cell. The quality factor (Q × f) increased with bond strength and lattice energy (Ucal), especially the lattice energy of the Si-O bond. The temperature coefficient of resonant frequency (τf) was determined by the susceptibility and lattice energy of the Cu/Co-O bond. The following optimum microwave dielectric properties were obtained at x = 0.15 when sintered at 1000 °C for 3 h: εr = 8.45, Q×f =58958 GHz and τf = -34.4 ppm/°C. 相似文献
143.
144.
145.
146.
Most researches on graphene/polymer composites are focusing on improving the mechanical and electrical properties of polymers at low graphene content instead of paying attention to constructing graphene’s macroscopic structures. In current study the homo-telechelic functionalized polyethylene glycols (FPEGs) were tailored with π-orbital-rich groups (namely phenyl, pyrene and di-pyrene) via esterification reactions, which enhanced the interaction between polyethylene glycol (PEG) molecules and chemical reduced graphene oxide (RGO) sheets. The π–π stacking interactions between graphene sheets and π-orbital-rich groups endowed the composite films with enhanced tensile strength and tunable electrical conductivity. The formation of graphene network structure mediated by the FPEGs fillers via π–π stacking non-covalent interactions should account for the experimental results. The experimental investigations were also complemented with theoretical calculation using a density functional theory. Atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), UV–vis and fluorescence spectroscopy were used to monitor the step-wise preparation of graphene composite films. 相似文献
148.
Multi-walled carbon nanotubes (MWCNTs) were chemically functionalized to prepare thermoplastic polyurethane (PU) composites with enhanced properties. In order to achieve a high compatibility of functionalized MWCNTs with the PU matrix, polycaprolactone diol (PCL), as one of PU’s monomers, was selectively grafted on the surface of MWCNTs (MWCNT–PCL), while carboxylic acid groups functionalized MWCNTs (MWCNT–COOH) and raw MWCNTs served as control. Both MWCNT–COOH and MWCNT–PCL improved the dispersion of MWCNTs in the PU matrix and interfacial bonding between them at 1 wt% loading fraction. The MWCNT–PCL/PU composite showed the greatest extent of improvement, where the tensile strength and modulus were 51.2% and 33.5% higher than those of pure PU respectively, without sacrificing the elongation at break. The considerable improvement in both mechanical properties and thermal stability of MWCNT–PCL/PU composite should result from the homogeneous dispersion of MWCNT–PCL in the PU matrix and strong interfacial bonding between them. 相似文献
149.
Undoped and fluorine doped ZnO thin films were deposited onto glass substrates using successive ionic layer adsorption and reaction (SILAR) technique and then annealed at 350 °C in vacuum ambience. The F doping level was varied from 0 to 15 at% in steps of 5 at%. The XRD analysis showed that all the films are polycrystalline with hexagonal wurtzite structure and preferentially oriented along the (002) plane. Crystallite sizes were found to increase when 5 at% of F is doped and then decreased with further doping. It was seen from the SEM images that the doping causes remarkable changes in the surface morphology and the annealing treatment results in well-defined grains with an improvement in the grain size irrespective of doping level. All the films exhibit good transparency (>70%) after vacuum annealing. Electrical resistivity of the film was found to be minimum (1.32×10−3 Ω cm) when the fluorine doping level was 5 at%. 相似文献
150.
Joo H. Kang Eujin Um Alexander Diaz Harry Driscoll Melissa J. Rodas Karel Domansky Alexander L. Watters Michael Super Howard A. Stone Donald E. Ingber 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(42):5657-5666
Magnetic nanoparticles have been employed to capture pathogens for many biological applications; however, optimal particle sizes have been determined empirically in specific capturing protocols. Here, a theoretical model that simulates capture of bacteria is described and used to calculate bacterial collision frequencies and magnetophoretic properties for a range of particle sizes. The model predicts that particles with a diameter of 460 nm should produce optimal separation of bacteria in buffer flowing at 1 L h−1. Validating the predictive power of the model, Staphylococcus aureus is separated from buffer and blood flowing through magnetic capture devices using six different sizes of magnetic particles. Experimental magnetic separation in buffer conditions confirms that particles with a diameter closest to the predicted optimal particle size provide the most effective capture. Modeling the capturing process in plasma and blood by introducing empirical constants (ce), which integrate the interfering effects of biological components on the binding kinetics of magnetic beads to bacteria, smaller beads with 50 nm diameters are predicted that exhibit maximum magnetic separation of bacteria from blood and experimentally validated this trend. The predictive power of the model suggests its utility for the future design of magnetic separation for diagnostic and therapeutic applications. 相似文献