全文获取类型
收费全文 | 94642篇 |
免费 | 10963篇 |
国内免费 | 6879篇 |
专业分类
电工技术 | 8625篇 |
技术理论 | 3篇 |
综合类 | 9153篇 |
化学工业 | 12768篇 |
金属工艺 | 6100篇 |
机械仪表 | 6731篇 |
建筑科学 | 8046篇 |
矿业工程 | 2870篇 |
能源动力 | 2656篇 |
轻工业 | 8505篇 |
水利工程 | 2678篇 |
石油天然气 | 3558篇 |
武器工业 | 1113篇 |
无线电 | 11091篇 |
一般工业技术 | 9631篇 |
冶金工业 | 3110篇 |
原子能技术 | 1486篇 |
自动化技术 | 14360篇 |
出版年
2024年 | 269篇 |
2023年 | 1565篇 |
2022年 | 3244篇 |
2021年 | 4524篇 |
2020年 | 3429篇 |
2019年 | 2532篇 |
2018年 | 2702篇 |
2017年 | 3118篇 |
2016年 | 2803篇 |
2015年 | 4068篇 |
2014年 | 5115篇 |
2013年 | 6125篇 |
2012年 | 7503篇 |
2011年 | 7836篇 |
2010年 | 7251篇 |
2009年 | 7012篇 |
2008年 | 7113篇 |
2007年 | 6645篇 |
2006年 | 6159篇 |
2005年 | 4816篇 |
2004年 | 3468篇 |
2003年 | 2808篇 |
2002年 | 3030篇 |
2001年 | 2749篇 |
2000年 | 1990篇 |
1999年 | 1186篇 |
1998年 | 682篇 |
1997年 | 576篇 |
1996年 | 456篇 |
1995年 | 368篇 |
1994年 | 290篇 |
1993年 | 219篇 |
1992年 | 191篇 |
1991年 | 134篇 |
1990年 | 100篇 |
1989年 | 95篇 |
1988年 | 61篇 |
1987年 | 55篇 |
1986年 | 35篇 |
1985年 | 33篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 23篇 |
1981年 | 14篇 |
1980年 | 25篇 |
1979年 | 13篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1959年 | 12篇 |
1951年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
21.
Yi Qin Tao Xiong Ting Zhao Jianfeng Zhu Jun Yang Yi Liu Xingang Kong Xiaohan Li 《Ceramics International》2021,47(9):12641-12650
The strengthening method of multi-element M-site solid solution is a common approach to improve mechanical properties of MAX phase ceramic. However, the research on capability of multi-element A-site solid solution to improve mechanical properties has rarely been reported. Thereupon, quasi-high-entropy MAX phase ceramic bulks of Ti2(Al1?xAx)C and Ti3(Al1?xAx)C2 (A = Ga, In, Sn, x = 0.2, 0.3, 0.4) were successfully synthesized by in situ vacuum hot pressing via multi-elements solid solution. The multi-elements solid solution in single-atom thick A layer was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy as well as by energy dispersive X-ray spectroscopy mappings. Effects of doped multi-elements contents on the phase, microstructure, mechanical properties, and high temperature tribological behaviors were studied. Results demonstrated that the Vickers hardness, anisotropic flexural strength, fracture toughness, and tribological properties of Ti–Al–C based MAX ceramics could be remarkably improved by constitution of quasi-high-entropy MAX phase in A layers. Moreover, the strengthening and wear mechanisms were also discussed in detail. This method of multi-element solid solution at A-site provides new way to enhance mechanical properties of other MAX phase ceramics. 相似文献
22.
共同购买网络的推荐系统应用越加广泛,仅基于网络内生结构变量研究其共同购买链接的经济意义已有局限,故加入网络口碑这一外生变量,进行更全面的分析。采用了社会网络方法中指数随机图模型进行建模,主要围绕产品销售量、产品入度、差评率和评论数4个方面因素,探究其对共同购买网络中共同购买链接形成的影响。结果显示,销售量、产品入度和评论数对共同购买链接形成的影响呈正比关系,而差评率则会显著地降低产品共同购买的几率。该指数随机图构建出的共同购买网络为在线电商平台管理网络口碑和推荐系统优化设计提供有益参考。 相似文献
23.
24.
25.
Wenfei Tian Yi Zheng Weiqun Wang Donghai Wang Michael Tilley Guorong Zhang Zhonghu He Yonghui Li 《Comprehensive Reviews in Food Science and Food Safety》2022,21(3):2274-2308
The health benefits of whole wheat consumption can be partially attributed to wheat's phytochemicals, including phenolic acids, flavonoids, alkylresorcinols, carotenoids, phytosterols, tocopherols, and tocotrienols. It is of increasing interest to produce whole wheat products that are rich in bioactive phytochemicals. This review provides the fundamentals of the chemistry, extraction, and occurrence of wheat phytochemicals and includes critical discussion of several long-lasting issues: (1) the commonly used nomenclature on distribution of wheat phenolic acids, namely, soluble-free, soluble-conjugated, and insoluble-bound phenolic acids; (2) different extraction protocols for wheat phytochemicals; and (3) the chemistry and application of in vitro antioxidant assays. This review further discusses recent advances on the effects of genotypes, environments, field management, and processing techniques including ultrafine grinding, germination, fermentation, enzymatic treatments, thermal treatments, and food processing. These results need to be interpreted with care due to varied sample preparation protocols and limitations of in vitro assays. The bioaccessibility, bioavailability, metabolism, and potential health benefits of wheat phytochemicals are also reviewed. This comprehensive and critical review will benefit scientific researchers in the field of bioactive compounds of cereal grains and also those in the cereal food industry to produce high-quality functional foods. 相似文献
27.
Here, highly‐oriented poly(m‐phenylene isophthalamide)/polyacrylonitrile multi‐walled carbon nanotube (PMIA/PAN‐MWCNT) composite nanofiber membranes with excellent mechanical strength and thermal stability are successfully produced using electrospinning. It is demonstrated that the cooperation of multi‐walled carbon nanotubes (MWCNT) and high‐speed rotating collection is beneficial to the acquisition of highly oriented fibers and effectively improves the mechanical strength of the membrane along the orientation direction. Specifically, the tensile stress of poly(m‐phenylene isophthalamide)/polyacrylonitrile (PMIA/PAN) membrane is enhanced significantly from 10.6 to 20.7 MPa, benefiting from the highly oriented alignment of the fibers as well as the reinforcing effect of MWCNTs on the fibers. Furthermore, the stressing process of single fiber and fiber aggregates is carefully simulated, and the influence of MWCNTs on the mechanical properties of PMIA/PAN‐MWCNT membranes is analyzed comprehensively, providing a meaningful auxiliary means for the study of mechanical properties. In addition, the composite nanofiber membrane has the advantages of both PMIA and PAN, possessing high temperature resistance, flame‐retardancy, and chemical stability, for an ideal high‐temperature material. In short, the as‐prepared PMIA/PAN‐MWCNT composite membrane with excellent comprehensive property emerges a promising application in many fields, especially in high‐tech. 相似文献
28.
29.
在模拟车用有机朗肯循环(organic Rankine cycle,ORC)系统的工作环境下,设计并搭建以R123作为工质的液压隔膜计量泵性能测试平台。在额定转速(2900 r/min)下,通过调节液压隔膜计量泵的冲程(25%、50%、75%、100%)和出口压力,得到变工况下液压隔膜计量泵的特性曲线,并分析液压隔膜计量泵的关键参数对车用ORC系统性能的影响情况。结果表明:液压隔膜计量泵的流量受冲程影响,与出口压力基本无关。其输入功率和实际运行效率均随着冲程的增加而升高,最高分别可达523.91 W、88.27%。应用该液压隔膜计量泵的模拟车用ORC系统吸热量变化范围较广,系统热效率最高可达12.81%。液压隔膜计量泵可应用于车用ORC系统,通过调节液压隔膜计量泵的冲程和出口压力,可实现提高车用ORC系统热效率、增加系统净输出功率的目的。 相似文献
30.
为分析单层石墨烯纳米片对核态池沸腾换热的影响机理,对基液为R141b、分散相为单层石墨烯纳米片的纳米制冷剂的核态池沸腾换热特征进行了测定,采用Hot Disk热物性分析仪和铂金板法分别测定了石墨烯纳米制冷剂的热导率和表面张力,采用接触角测量仪和扫描电子显微镜(SEM)观测了沸腾后加热表面的润湿性和形貌特征。实验中,单层石墨烯纳米片的质量百分含量(ω)为0.02%~0.50%,实验压力为一个标准大气压,热流密度为20~200 kW/m2。实验结果表明:单层石墨烯纳米片的加入,使制冷剂R141b的核态池沸腾换热得到强化;当ω=0.2%时,换热系数提高比例出现峰值,为57.7%。伴随ω的增加,石墨烯纳米制冷剂的热导率增大、表面张力减小,沸腾表面润湿性增强且微腔数先增后减,综合作用的结果导致存在一个最佳的单层石墨烯纳米片浓度(即ω=0.2%)使换热系数最高。 相似文献