全文获取类型
收费全文 | 224436篇 |
免费 | 17225篇 |
国内免费 | 8721篇 |
专业分类
电工技术 | 12053篇 |
技术理论 | 11篇 |
综合类 | 12592篇 |
化学工业 | 36816篇 |
金属工艺 | 13418篇 |
机械仪表 | 13911篇 |
建筑科学 | 14126篇 |
矿业工程 | 5916篇 |
能源动力 | 5235篇 |
轻工业 | 12812篇 |
水利工程 | 4166篇 |
石油天然气 | 13164篇 |
武器工业 | 1556篇 |
无线电 | 24413篇 |
一般工业技术 | 33624篇 |
冶金工业 | 13699篇 |
原子能技术 | 5418篇 |
自动化技术 | 27452篇 |
出版年
2024年 | 811篇 |
2023年 | 3118篇 |
2022年 | 5864篇 |
2021年 | 8440篇 |
2020年 | 6314篇 |
2019年 | 5472篇 |
2018年 | 6749篇 |
2017年 | 7355篇 |
2016年 | 6785篇 |
2015年 | 7846篇 |
2014年 | 10008篇 |
2013年 | 12229篇 |
2012年 | 13335篇 |
2011年 | 14415篇 |
2010年 | 12182篇 |
2009年 | 11874篇 |
2008年 | 11611篇 |
2007年 | 11020篇 |
2006年 | 10825篇 |
2005年 | 9130篇 |
2004年 | 6813篇 |
2003年 | 6405篇 |
2002年 | 6262篇 |
2001年 | 5693篇 |
2000年 | 5237篇 |
1999年 | 4947篇 |
1998年 | 4069篇 |
1997年 | 3404篇 |
1996年 | 3059篇 |
1995年 | 2629篇 |
1994年 | 2239篇 |
1993年 | 1779篇 |
1992年 | 1614篇 |
1991年 | 1421篇 |
1990年 | 1324篇 |
1989年 | 1204篇 |
1988年 | 1060篇 |
1987年 | 934篇 |
1986年 | 842篇 |
1985年 | 765篇 |
1984年 | 725篇 |
1982年 | 692篇 |
1979年 | 746篇 |
1978年 | 784篇 |
1977年 | 744篇 |
1976年 | 769篇 |
1975年 | 722篇 |
1974年 | 721篇 |
1973年 | 727篇 |
1972年 | 709篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
142.
Kazantsev Yu. N. Kraftmakher G. A. Mal’tsev V. P. 《Journal of Communications Technology and Electronics》2019,64(6):550-554
Journal of Communications Technology and Electronics - Approximate formulas for calculating the coefficient of reflection from an artificial magnetic conductor (AMC) based on a capacitive lattice... 相似文献
143.
Guangbo Zeng Dongqing Zhang Liuming Yan Baohua Yue Ting Pan Yidong Hu Shufa He Hongbin Zhao Jiujun Zhang 《International Journal of Hydrogen Energy》2021,46(39):20664-20677
Side-chain optimized poly (2,6-dimethyl-1,4-phenylene oxide)-g-poly (styrene sulfonic acid) (PPO-g-PSSA) is designed with balanced water-resistance and sulfonation degree. The PPO-g-PSSA is synthesized by controlled atom-transfer radical polymerization (ATRP) from brominated poly (2,6-dimethyl-1,4-phenylene oxide) (PPO-xBr) and ethyl styrene-4-sulfonate and followed by hydrolysis. A series of PPO-g-PSSA are prepared possessing different bromination degree (x) of PPO-xBr and polymerization degree (m) of the side-chains and the water-resistances of the fabricated membranes are investigated. The results show that a PPO-g-PSSA at relatively low x (x < 0.2) and high m (m > 4) exhibits good balance between the water-resistance and the sulfonation degree. Namely, it displays suitable proton conductivity with compromised water-resistance. Moreover, a maximum ion exchange capacity (IEC) of 3.24 mmol g?1 is reached without the sacrifice of water-resistance. In addition, PPO-g-0.08PSSA-13 and PPO-g-0.14PSSA-4 are chosen characterized by thermogravimetric analysis, proton conductivities and mechanical properties. At 90% RH, the optimized PPO-g-0.08PPSA-13 possesses a proton conductivity of 37.9 mS cm?1 at 40 °C and 45.5 mS cm?1 at 95 °C, respectively. 相似文献
144.
Zinov’eva I. V. Fedorov A. Ya. Milevskii N. A. Zakhodyaeva Yu. A. Voshkin A. A. 《Theoretical Foundations of Chemical Engineering》2021,55(4):663-670
Theoretical Foundations of Chemical Engineering - A choline chloride–sulfosalicylic acid deep eutectic solvent (DES) is proposed for dissolving the oxides Co(II), Cu(II), Zn(II), Fe(III),... 相似文献
145.
Chertkov Yu. B. Anikin M. N. Lebedev I. I. Naimushin A. G. Smol’nikov N. V. 《Atomic Energy》2021,131(1):42-45
Atomic Energy - The results of calculations and experimental determination of the neutronics characteristics of the IRT-T research reactor are presented. The IRT-T reactor is a pool reactor with... 相似文献
146.
Jiajia Ye Xuting Li Guang Xia Guanghao Gong Zhiqiang Zheng Chuanzhong Chen Cheng Hu 《材料科学技术学报》2021,77(18):100-107
We report for the first time a Na-ion battery anode material composed of P-doped CoSe2 nanoparticles(P-CoSe2)with the size of 5-20 nm that are uniformly embed in a 3D porous honeycomb-like carbon network.High rate capability and cycling stability are achieved simultaneously.The honeycomb-like carbon network is rationally designed to support high electrical conductivity,rapid Na-ion diffusion as well as the accommodation of the volume expansion from the active P-CoSe2 nanoparticles.In particular,heteroatom P-doping within CoSe2 introduces stronger P-Co bonds and additional P-Se bonds that signif-icantly improve the structure stability of P-CoSe2 for highly stable sodiation/desodiation over long-term cycling.P-doping also improves the electrical conductivity of the CoSe2 nanoparticles,leading to highly elevated electrochemical kinetics to deliver high specific capacities at high current densities.Benefiting from the unique nanostructure and atomic-level P-doping,the P-CoSe2(2∶1)/C anode delivers an excel-lent cycle stability with a specific capacity of 206.9 mA h g-1 achieved at 2000 mA g-1 after 1000 cycles.In addition,this material can be synthesized using a facile pyrolysis and selenization/phosphorization approach.This study provides new opportunities of heteroatom doping as an effective method to improve the cycling stability of Na-ion anode materials. 相似文献
147.
Baofu Qiu Xiaoming Duan Zhuo Zhang Delong Cai Ning Liao Peigang He Dechang Jia Yu Zhou 《Ceramics International》2021,47(1):73-79
The effects of La2O3–Al2O3–SiO2 addition on the thermal conductivity, coefficient of thermal expansion (CTE), Young's modulus and cyclic thermal shock resistance of hot-pressed h-BN composite ceramics were investigated. The samples were heated to 1000 °C and then quenched to room temperature with 1–50 cycles, and the residual flexural strength was used to evaluate cyclic thermal shock resistance. h-BN composite ceramics containing 10 vol% La2O3–Al2O3 and 20 vol% SiO2 addition exhibited the highest flexural strength, thermal conductivity and relatively low CTE, which were beneficial to the excellent thermal shock resistance. In addition, the viscous amorphous phase of ternary La2O3–Al2O3–SiO2 system could accommodate and relax thermal stress contributing to the high thermal shock resistance. Therefore, the residual flexural strength still maintained the value of 234.3 MPa (86.9% of initial strength) after 50 cycles of thermal shock. 相似文献
148.
149.
Water Resources Management - Public awareness of water quality concerns has increased since the Flint, MI crisis, but knowledge about water resources management remains low. Consequently,... 相似文献
150.
A size-dependent governing equation is derived to investigate the torsional static behaviors of two-dimensionally functionally graded microtubes based on the modified couple stress theory. The shear modulus is assumed to vary along the tube’s length direction according to an exponential distribute function, and varies along the tube’s radius direction according to a power-law function. A generalized differential quadrature method is developed to determine the rotational angle and shear stresses. Some illustrative examples are given to investigate the effects of applied torques, the length scale parameter and various material compositions on the torsional angle and shear stresses. 相似文献