全文获取类型
收费全文 | 128183篇 |
免费 | 15127篇 |
国内免费 | 8326篇 |
专业分类
电工技术 | 5635篇 |
技术理论 | 1篇 |
综合类 | 9238篇 |
化学工业 | 32598篇 |
金属工艺 | 10334篇 |
机械仪表 | 6453篇 |
建筑科学 | 6596篇 |
矿业工程 | 2673篇 |
能源动力 | 3328篇 |
轻工业 | 7734篇 |
水利工程 | 1602篇 |
石油天然气 | 4424篇 |
武器工业 | 1043篇 |
无线电 | 15225篇 |
一般工业技术 | 15703篇 |
冶金工业 | 4980篇 |
原子能技术 | 1839篇 |
自动化技术 | 22230篇 |
出版年
2024年 | 422篇 |
2023年 | 2005篇 |
2022年 | 3885篇 |
2021年 | 4413篇 |
2020年 | 3693篇 |
2019年 | 3425篇 |
2018年 | 3232篇 |
2017年 | 3814篇 |
2016年 | 4489篇 |
2015年 | 4283篇 |
2014年 | 9105篇 |
2013年 | 8614篇 |
2012年 | 10162篇 |
2011年 | 12390篇 |
2010年 | 9802篇 |
2009年 | 10350篇 |
2008年 | 7532篇 |
2007年 | 7837篇 |
2006年 | 7057篇 |
2005年 | 5820篇 |
2004年 | 4627篇 |
2003年 | 4302篇 |
2002年 | 3408篇 |
2001年 | 2672篇 |
2000年 | 2498篇 |
1999年 | 2005篇 |
1998年 | 1542篇 |
1997年 | 1188篇 |
1996年 | 1095篇 |
1995年 | 868篇 |
1994年 | 816篇 |
1993年 | 650篇 |
1992年 | 537篇 |
1991年 | 467篇 |
1990年 | 361篇 |
1989年 | 301篇 |
1988年 | 211篇 |
1987年 | 195篇 |
1986年 | 218篇 |
1985年 | 169篇 |
1984年 | 133篇 |
1983年 | 121篇 |
1982年 | 114篇 |
1981年 | 119篇 |
1980年 | 120篇 |
1979年 | 92篇 |
1978年 | 82篇 |
1977年 | 88篇 |
1976年 | 100篇 |
1975年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 217 毫秒
91.
92.
Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers (HCTs) during direct shear of infilled joints under constant normal stiffness (CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using three-dimensional (3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients (JRCs) of 8–10 and 18–20 with the ratios of infill thickness to asperity height (t/a) equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness. 相似文献
93.
94.
Peng Jiang Jiafeng Lu Kun Li Xiquan Chen Ruiqi Dan 《Fullerenes, Nanotubes and Carbon Nanostructures》2020,28(5):381-386
AbstractPreparation condition can affect the structure and the properties of nanofiber membrane. In order to explore suitable conditions to prepare the Fe3O4/PVDF nanofiber membrane with good hydrophobicity, the hydrophobicity of Fe3O4/PVDF nanofiber membranes obtained by electrospinning was investigated by changing preparation conditions like weight percentage of Fe3O4 nanoparticles, blending quality concentration of poly (vinylidene fluoride) (PVDF) and Fe3O4 nanoparticles, and positive voltage. And the variations of hydrophobicity of Fe3O4/PVDF nanofiber membranes modified by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane were studied. The results show that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has changed under different preparation conditions. The contact angles of samples increased after a modification by 1H, 1H, 2H, 2H-perfluorodecyl trimethoxysilane, which indicates that the hydrophobicity of Fe3O4/PVDF nanofiber membranes has been enhanced. 相似文献
95.
96.
Eicosapentaenoic acid (EPA) production by an oleaginous fungus Mortierella alpina expressing heterologous the Δ17‐desaturase gene under ordinary temperature 下载免费PDF全文
97.
Han Yan Gu Yi Chen Lei Li Bing Liu Xiang Ming Chen 《International Journal of Applied Ceramic Technology》2020,17(2):790-796
SrLa[Ga1−x(R0.5Ti0.5)x]O4 (R = Mg, Zn) ceramics were prepared by a standard solid state sintering method. The single-phase ceramics with K2NiF4-type layered perovskite structure and I4/mmm space group were obtained, indicating that SrLa(R0.5Ti0.5) and SrLaGaO4 can form the unlimited solid solutions. With increasing x for R = Mg and Zn, εr increases monotonously, the Qf value first increases and then decreases, while τf increases from a negative to a positive value. The optimized microwave dielectric properties were obtained as following: εr = 23.3, Qf = 89 400 GHz, τf = −0.8 ppm/°C for SrLa[Ga0.6(Mg0.5Ti0.5)0.4]O4 and εr = 23.3, Qf = 76 200 GHz, τf = 0.2 ppm/°C for SrLa[Ga0.7(Zn0.5Ti0.5)0.3]O4, indicating that the present solid solution ceramics are the promising candidates as microwave resonator materials for the telecommunication applications. 相似文献
98.
F. Schröder R. M. Ward A. R. Walpole R. P. Turner M. M. Attallah J.-C. Gebelin 《Materials Science & Technology》2015,31(3):372-384
Linear friction welding of the Ti6Al4V alloy is studied. A new definition of the energy input rate is proposed, based on an integration over time of the in-plane force and velocity; a strong correlation with the upset rate is then found. The effective friction coefficient is estimated to be 0·5±0·1 for varying frequencies and amplitudes, with only a weak dependence on the processing conditions displayed. A model is proposed that accounts for both the conditioning and equilibrium stages of the process, which is shown to be in good agreement with the experimental data. The model is used to study the mechanism by which the flash is formed. A criterion is proposed by which the rippled nature of its morphology can be predicted. 相似文献
99.
《Ceramics International》2020,46(3):2868-2876
In order to improve the stability of PZT-based sensors, the mechanical, dielectric, ferroelectric and piezoelectric properties of PZT-5H under impact load were studied experimentally by using the separated Hopkinson pressure bar (SHPB) with an electrical output measurement device. At the same time, the experimental study on the material properties of PZT-5H before and after the impact was carried out. The effect of impact cracks on the output voltage of PZT-5H was also analyzed. The results show that the dynamic piezoelectric constants of PZT-5H under low stress impact (10–50 MPa) are different from those under quasi-static state, and the empirical relationship between them and the peak stress is obtained through experiments. The dielectric properties of PZT-5H did not change under low stress impact, but micro-cracks occurred in the material and dielectric loss increased at high frequencies. Under short circuit, the residual polarization intensity of PZT-5H decreases sharply due to impact load. While the impact load causes the secondary polarization and the increase of the residual polarization intensity of PZT under open circuit. When the stress is over 45 MPa, the PZT-5H breaks. The formation of cracks causes abnormal discharge voltage and gap discharge. 相似文献
100.