全文获取类型
收费全文 | 167329篇 |
免费 | 15509篇 |
国内免费 | 9427篇 |
专业分类
电工技术 | 11172篇 |
技术理论 | 13篇 |
综合类 | 12249篇 |
化学工业 | 25795篇 |
金属工艺 | 10157篇 |
机械仪表 | 11135篇 |
建筑科学 | 14020篇 |
矿业工程 | 5231篇 |
能源动力 | 5060篇 |
轻工业 | 11202篇 |
水利工程 | 3653篇 |
石油天然气 | 8968篇 |
武器工业 | 1804篇 |
无线电 | 20077篇 |
一般工业技术 | 18947篇 |
冶金工业 | 7362篇 |
原子能技术 | 2282篇 |
自动化技术 | 23138篇 |
出版年
2024年 | 677篇 |
2023年 | 2377篇 |
2022年 | 4460篇 |
2021年 | 6310篇 |
2020年 | 4807篇 |
2019年 | 4095篇 |
2018年 | 4422篇 |
2017年 | 5205篇 |
2016年 | 4807篇 |
2015年 | 6767篇 |
2014年 | 8566篇 |
2013年 | 10054篇 |
2012年 | 11606篇 |
2011年 | 12606篇 |
2010年 | 11526篇 |
2009年 | 11029篇 |
2008年 | 11005篇 |
2007年 | 10764篇 |
2006年 | 10474篇 |
2005年 | 8603篇 |
2004年 | 6193篇 |
2003年 | 5178篇 |
2002年 | 5027篇 |
2001年 | 4385篇 |
2000年 | 3814篇 |
1999年 | 3457篇 |
1998年 | 2662篇 |
1997年 | 2199篇 |
1996年 | 2005篇 |
1995年 | 1558篇 |
1994年 | 1406篇 |
1993年 | 1003篇 |
1992年 | 744篇 |
1991年 | 594篇 |
1990年 | 439篇 |
1989年 | 372篇 |
1988年 | 301篇 |
1987年 | 205篇 |
1986年 | 158篇 |
1985年 | 100篇 |
1984年 | 58篇 |
1983年 | 60篇 |
1982年 | 58篇 |
1981年 | 41篇 |
1980年 | 27篇 |
1979年 | 13篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1959年 | 19篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
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
83.
84.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
85.
Yong Pan Chen Zhu Wen Bin Zeng Pei Fu Chi Chen Bao Ming Xu Zhong Feng Gao 《Chembiochem : a European journal of chemical biology》2021,22(24):3431-3436
Rapid and sensitive point-of-care testing (POCT) is an extremely critical mission in practical applications, especially for rigorous military medicine, home health care, and in the third world. Here, we report a visual POCT method for adenosine triphosphate (ATP) detection based on Taylor rising in the corner of quadratic geometries between two rod surfaces. We discuss the principle of Taylor rising, demonstrating that it is significantly influenced by contact angle, surface tension, and density of the sample, which are controlled by ATP-dependent rolling circle amplification (RCA). In the presence of ATP, RCA reaction effectively suppresses Taylor-rising behavior, due to the increased contact angle, density, and decreased surface tension. Without addition of ATP, untriggered RCA reaction is favorable for Taylor rising, resulting in a significant height. With this proposed method, visual sensitive detection of ATP without the aid of other instruments is realized with only a 5 μL droplet, which has good selectivity and a low detection limit (17 nM). Importantly, this visual method provides a promising POCT tool for user-friendly molecular diagnostics. 相似文献
86.
Zhen Wu Jing Yao Pengfei Zhu Fusheng Yang Xiangyu Meng Sandra Kurko Zaoxiao Zhang 《International Journal of Hydrogen Energy》2021,46(19):11183-11198
Advanced biogas power generation technology has been attracting attentions, which contributes to the waste disposal and the mitigation of greenhouse gas emissions. This work proposes and models a novel biogas-fed hybrid power generation system consisting of solid oxide fuel cell, water gas shift reaction, thermal swing adsorption and proton exchange membrane fuel cell (SOFC-WGS-TSA-PEMFC). The thermodynamic, exergetic, and thermo-economic analyses of this hybrid system for power generation were conducted to comprehensively evaluate its performance. It was found that the novel biogas-fed hybrid system has a gross energy conversion efficiency of 68.63% and exergy efficiency of 65.36%, indicating high efficiency for this kind of hybrid power technology. The market sensitivity analysis showed that the hybrid system also has a low sensitivity to market price fluctuation. Under the current subsidy level for the distributed biogas power plant, the levelized cost of energy can be lowered to 0.02942 $/kWh for a 1 MW scale system. Accordingly, the payback period and annual return on investment can reach 1.4 year and about 20%, respectively. These results reveal that the proposed hybrid system is promising and economically feasible as a distributed power plant, especially for the small power scale (no more than 2 MW). 相似文献
87.
The support flux was first investigated as a separate influencing factor for its effect on performances of ceramic filtration membranes. Three pre-membranes were prepared by tape-casting and then transfer-coated to supports to form dual-layer ceramic membranes after sintering. Experiments demonstrated that membrane layers with almost the same properties were obtained despite the huge difference in support flux. When the support flux increases from 3.120 to 97.53 m3m?2h?1, the flux of these three membrane series have increased by 75%, 186% and 228%, respectively. Experimental rules can provide structural design and evaluation from the perspective of permeability. The limit membrane flux of a certain system was derived according to the resistance distribution law of internal membrane structure and the Darcy's theorem. On this basis, a method for designing support flux was proposed. Furthermore, we present a criterion to quickly and easily evaluate the match between the support and the top layer, which is the ratio of membrane resistance to total resistance. Finally, the filtration resistance of penetration caused by suction of membrane particles into the support was measured for the first time, taking the advantage of the transfer-coating method that inherently free of penetration. Our works are expected to deepen the understanding of the ceramic membrane structure and provided guidance for its rational design and optimization. 相似文献
88.
对PCB废水总氮的处理,从源头削减、分质收集、分质预处理到末端处理提出了多种方法,着重分析了MAP+管式微滤膜处理氨氮废水、多级组合式RO处理硝态氮废水和A2O+MBR处理综合废水,提出PCB废水总氮达标的组合工艺,项目建成后达到预期效果。 相似文献
89.
90.
Tingen Zhu Wenping Li Qiqing Wang Yanbo Hu Kaifang Fan Jiafa Du 《Mine Water and the Environment》2020,39(1):57-67
A method to calculate the height of a water-conducting fractured zone (HWCFZ) was developed based on the plate and shell theory, and the development of the HWCFZ in bedrock and Q2l loess strata is discussed in detail. First, the subsidence-deflection curve equation of the overlying stratum is theoretically derived, and then the ultimate deflection and free space height of rock strata are calculated. Moreover, the strata tensile strain is calculated by using integral calculus. In addition, the failure state of the rock is analyzed by comparing the theoretically calculated tensile strain with the experimentally measured yield tensile strain, allowing one to attain the maximum value of HWCFZ. This approach was tested at the Jinjitan coal mine; the theoretically predicted, experimentally measured, and numerically computed maximum HWCFZ values were 189.5, 187.3, and 188.5 m, respectively, demonstrating the accuracy of the proposed method. These results are highly significant for safe and environment-friendly coal mining in northwest Shaanxi, China. 相似文献