全文获取类型
收费全文 | 100070篇 |
免费 | 10712篇 |
国内免费 | 5909篇 |
专业分类
电工技术 | 7059篇 |
技术理论 | 6篇 |
综合类 | 8126篇 |
化学工业 | 15768篇 |
金属工艺 | 5532篇 |
机械仪表 | 6555篇 |
建筑科学 | 8201篇 |
矿业工程 | 2997篇 |
能源动力 | 3095篇 |
轻工业 | 8223篇 |
水利工程 | 2154篇 |
石油天然气 | 5429篇 |
武器工业 | 1048篇 |
无线电 | 11851篇 |
一般工业技术 | 10769篇 |
冶金工业 | 3856篇 |
原子能技术 | 1094篇 |
自动化技术 | 14928篇 |
出版年
2024年 | 515篇 |
2023年 | 1945篇 |
2022年 | 3793篇 |
2021年 | 5131篇 |
2020年 | 3636篇 |
2019年 | 2961篇 |
2018年 | 3184篇 |
2017年 | 3429篇 |
2016年 | 3026篇 |
2015年 | 4362篇 |
2014年 | 5389篇 |
2013年 | 6034篇 |
2012年 | 6996篇 |
2011年 | 7405篇 |
2010年 | 6396篇 |
2009年 | 6154篇 |
2008年 | 5995篇 |
2007年 | 5541篇 |
2006年 | 5283篇 |
2005年 | 4349篇 |
2004年 | 3224篇 |
2003年 | 3261篇 |
2002年 | 3686篇 |
2001年 | 3106篇 |
2000年 | 2263篇 |
1999年 | 2046篇 |
1998年 | 1372篇 |
1997年 | 1178篇 |
1996年 | 1105篇 |
1995年 | 877篇 |
1994年 | 751篇 |
1993年 | 583篇 |
1992年 | 403篇 |
1991年 | 296篇 |
1990年 | 227篇 |
1989年 | 186篇 |
1988年 | 188篇 |
1987年 | 118篇 |
1986年 | 77篇 |
1985年 | 41篇 |
1984年 | 29篇 |
1983年 | 21篇 |
1982年 | 40篇 |
1981年 | 23篇 |
1980年 | 31篇 |
1979年 | 19篇 |
1976年 | 1篇 |
1971年 | 2篇 |
1959年 | 2篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
山西某矿5308底抽巷在掘进过程中速度慢、效率低,直接影响工作面的瓦斯抽采,为了改善上述情形,对炮孔间距进行研究。通过使用ANSYS软件对不同炮孔间距下快速掘进效果的模拟分析,并经现场验证,得出了适应该矿的最佳炮孔间距。结果表明:炮孔间距为500 mm时,爆破产生裂隙发育范围和岩石损伤区域都最大,快速掘进的效果最好。 相似文献
62.
63.
64.
65.
66.
In this research, the three‐dimensional structural and colorimetric modeling of three‐dimensional woven fabrics was conducted for accurate color predictions. One‐hundred forty single‐ and double‐layered woven samples in a wide range of colors were produced. With the consideration of their three‐dimensional structural parameters, three‐dimensional color prediction models, K/S‐, R‐, and L*a*b*‐based models, were developed through the optimization of previous two‐dimensional models which have been reported to be the three most accurate models for single‐layered woven structures. The accuracy of the new three‐dimensional models was evaluated by calculating the color differences ΔL*, ΔC*, Δh°, and ΔECMC(2:1) between the measured and the predicted colors of the samples, and then the error values were compared to those of the two‐dimensional models. As a result, there has been an overall improvement in color predictions of all models with a decrease in ΔECMC(2:1) from 10.30 to 5.25 units on average after the three‐dimensional modeling. 相似文献
67.
Zhuo Shi Ningning Dong Dingfeng Zhang Xiaofang Jiang Guanxin Du Shichao Lv Jiejie Chen Jun Wang Shifeng Zhou 《Journal of the American Ceramic Society》2019,102(7):3965-3971
The construction of nonlinear optical materials featuring asymmetric transmission of light is of great technological importance for various applications, including optical switching and optical power limiting. A significant challenge is the scalable fabrication of material candidates with good photochemical stability, high optical transmittance, and excellent optical limiting performance. Here, we present a nanocrystallization avenue for constructing hybrid optical limiting materials that exhibit ultrafast and robust optical limiting performance. The experimental results show that the controllable relaxation of a niobate glass may lead to the clustering of Nb-O units and contracting of the bandgap. It results in the notable improvement in nonlinear optical properties, including the enhanced saturation irradiance (380 GW/cm2), doubly increased nonlinear coefficient, and decreased limiting threshold (200 GW/cm2). Our results suggest a promising material that exhibits promising applications for protecting eyes and sensitive components from laser-induced damage. 相似文献
68.
Fei Xu Xiangli Shi Qingzhu Zhang Wenxing Wang 《International journal of molecular sciences》2015,16(8):18714-18731
The chlorothiophenoxy radicals (CTPRs) are key intermediate species in the formation of polychlorinated dibenzothiophenes/thianthrenes (PCDT/TAs). In this work, the formation of CTPRs from the complete series reactions of 19 chlorothiophenol (CTP) congeners with H and OH radicals were investigated theoretically by using the density functional theory (DFT) method. The profiles of the potential energy surface were constructed at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) contribution at 600–1200 K. The present study indicates that the structural parameters, thermal data, and rate constants as well as the formation potential of CTPRs from CTPs are strongly dominated by the chlorine substitution at the ortho-position of CTPs. Comparison with the study of formation of chlorophenoxy radicals (CPRs) from chlorophenols (CPs) clearly shows that the thiophenoxyl-hydrogen abstraction from CTPs by H is more efficient than the phenoxyl-hydrogen abstraction from CPs by H, whereas the thiophenoxyl-hydrogen abstraction from CTPs by OH is less impactful than the phenoxyl-hydrogen abstraction from CPs by OH. Reactions of CTPs with H can occur more readily than that of CTPs with OH, which is opposite to the reactivity comparison of CPs with H and OH. 相似文献
69.
70.
Yanlong Shi Xiaojuan Feng Haiyu Guan Jiahua Zhang Zhongai Hu 《International Journal of Hydrogen Energy》2021,46(12):8557-8566
Constructing high-efficient and nonprecious electrocatalysts is of primary importance for improving the efficiency of water splitting. Herein, a novel sunflower plate-like NiFe2O4/CoNi–S nanosheet heterostructure was fabricated via facile hydrothermal and electrodeposition methods. The as-fabricated NiFe2O4/CoNi–S heterostructure array exhibits remarkable bifunctional catalytic activity and stability toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. It presents a small overpotential of 219 mV and 149 mV for OER and HER, respectively, to produce a current density of 10 mA cm?2. More significantly, when the obtained electrodes are used as both the cathode and anode in an electrolyzer, a voltage of 1.57 V is gained at 10 mA cm?2, with superior stability for 72 h. Such outstanding properties are ascribed to: the 3D porous network structure, which exposes more active sites and accelerates mass transfer and gas bubble emission; the high conductivity of CoNi–S, which provides faster charge transport and thus promotes the electrocatalytic reaction of the composites; and the effective interface engineering between NiFe2O4 (excellent performance for OER) and CoNi–S (high activity for HER), which leads to a shorter transport pathway and thus expedites electron transfer. This work provides a new strategy for designing efficient and inexpensive electrocatalysts for water splitting. 相似文献