全文获取类型
收费全文 | 3830篇 |
免费 | 203篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 33篇 |
综合类 | 4篇 |
化学工业 | 1282篇 |
金属工艺 | 88篇 |
机械仪表 | 81篇 |
建筑科学 | 158篇 |
矿业工程 | 13篇 |
能源动力 | 105篇 |
轻工业 | 516篇 |
水利工程 | 24篇 |
石油天然气 | 13篇 |
无线电 | 238篇 |
一般工业技术 | 618篇 |
冶金工业 | 331篇 |
原子能技术 | 14篇 |
自动化技术 | 521篇 |
出版年
2024年 | 10篇 |
2023年 | 51篇 |
2022年 | 276篇 |
2021年 | 265篇 |
2020年 | 127篇 |
2019年 | 116篇 |
2018年 | 121篇 |
2017年 | 134篇 |
2016年 | 146篇 |
2015年 | 119篇 |
2014年 | 161篇 |
2013年 | 248篇 |
2012年 | 236篇 |
2011年 | 253篇 |
2010年 | 194篇 |
2009年 | 155篇 |
2008年 | 170篇 |
2007年 | 153篇 |
2006年 | 130篇 |
2005年 | 107篇 |
2004年 | 85篇 |
2003年 | 80篇 |
2002年 | 79篇 |
2001年 | 39篇 |
2000年 | 60篇 |
1999年 | 32篇 |
1998年 | 78篇 |
1997年 | 42篇 |
1996年 | 46篇 |
1995年 | 33篇 |
1994年 | 26篇 |
1993年 | 25篇 |
1992年 | 15篇 |
1991年 | 8篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 9篇 |
排序方式: 共有4039条查询结果,搜索用时 15 毫秒
91.
Bernette M. Oosterlaken Yifei Xu Mark M. J. van Rijt Marina Pilz da Cunha Gilles H. Timmermans Michael G. Debije Heiner Friedrich Albertus P. H. J. Schenning Nico A. J. M. Sommerdijk 《Advanced functional materials》2020,30(6)
In this work, a nanohybrid material based on a freestanding polymeric liquid crystal network capable of postmodification via cation exchange to tune birefringence is proposed. The smectic liquid crystal films can be infiltrated with a variety of cations, thereby changing the refractive indices (ne and no) and the effective birefringence (Δn) of the nanohybrid material, with reversible cation infiltration occurring within minutes. Birefringence could be tuned between values of 0.06 and 0.19, depending on the cation infiltrated into the network. Upon infiltration, a decrease in the smectic layer spacing is found with layer contraction independent of the induced change in birefringence. Potential applications are in the field of specialty optical devices, such as flexible, retunable reflective filters. 相似文献
92.
全封闭式压缩机腔内强烈的声场反映了主要的壳体激发源以及因之产生的噪声辐射。吸气消音器的振动以及机体和电动机表面的辐射激发了这个声场。在对机体、电机表面、数值解法和与机壳的耦合等做不同几何简化的情况下,本文对腔内声场进行了数值分析。模拟结果得到了实验证实,具有良好的一致性。本模型适用于声能向机壳的传播以及向外部环境辐射时分析各参数的影响。 相似文献
93.
94.
Giulia Poli Consuelo Fabi Chiara Sugoni Marina Maria Bellet Claudio Costantini Giovanni Luca Stefano Brancorsini 《International journal of molecular sciences》2022,23(9)
Varicocele (VC) is the most common abnormality identified in men evaluated for hypofertility. Increased levels of reactive oxygen species (ROS) and reduced antioxidants concentrations are key contributors in varicocele-mediated hypofertility. Moreover, inflammation and alterations in testicular immunity negatively impact male fertility. In particular, NLRP3 inflammasome activation was hypothesized to lead to seminal inflammation, in which the levels of specific cytokines, such as IL-1β and IL-18, are overexpressed. In this review, we described the role played by oxidative stress (OS), inflammation, and NLRP3 inflammasome activation in VC disease. The consequences of ROS overproduction in testis, including inflammation, lipid peroxidation, mitochondrial dysfunction, chromatin damage, and sperm DNA fragmentation, leading to abnormal testicular function and failed spermatogenesis, were highlighted. Finally, we described some therapeutic antioxidant strategies, with recognized beneficial effects in counteracting OS and inflammation in testes, as possible therapeutic drugs against varicocele-mediated hypofertility. 相似文献
95.
Roman Galchenko Qing Liu Yan Gao Yu Liu David He Josh Zhang Huailiang Liu Xiaohua Ke 《钻探工程》2021,48(10):1-12
过去十年,非常规油气勘探开发在全球范围内大幅扩张。水平钻井和多级水力压裂技术也在不断地发展和创新,使得超长水平井成为可能。同时,因为压裂强度不断增加,作业者可以最大限度地提高储层接触面积和对储层的改造体积 (SRV)。然而,完井优化方面的挑战仍然存在,作业者持续不断地尝试和试验各种完井与增产参数组合,以确保非常规油气藏开发的经济可行性。优选最佳的完井与增产参数组合是一项非常关键的任务,应结合油气田的具体储层特征进行优化。本文总结了2014—2020年间北美9个主要非常规油气藏的压裂增产趋势,包括Marcellus, Haynesville, Barnett, Utica, Bone Spring, Bakken, Wolfcamp Midland, Eagle Ford, Scoop/Stack。分析了各油气田几个关键的完井和增产参数的整体趋势,同时还评估了单个参数(如水平段压裂长度、支撑剂强度、段间距等)对井产能的影响。然后对比分析相应的初始井产量(90 天平均初始产量),评估各个参数对产能的影响,从而确定每个完井参数的最佳范围,以实现产能最优化。 相似文献
96.
Richard Rowe Gabriela D. Roman Frank P. McKenna Edward Barker Damian Poulter 《Accident; analysis and prevention》2015
The Driver Behavior Questionnaire (DBQ) is a self-report measure of driving behavior that has been widely used over more than 20 years. Despite this wealth of evidence a number of questions remain, including understanding the correlation between its violations and errors sub-components, identifying how these components are related to crash involvement, and testing whether a DBQ based on a reduced number of items can be effective. We address these issues using a bifactor modeling approach to data drawn from the UK Cohort II longitudinal study of novice drivers. This dataset provides observations on 12,012 drivers with DBQ data collected at .5, 1, 2 and 3 years after passing their test. A bifactor model, including a general factor onto which all items loaded, and specific factors for ordinary violations, aggressive violations, slips and errors fitted the data better than correlated factors and second-order factor structures. A model based on only 12 items replicated this structure and produced factor scores that were highly correlated with the full model. The ordinary violations and general factor were significant independent predictors of crash involvement at 6 months after starting independent driving. The discussion considers the role of the general and specific factors in crash involvement. 相似文献
97.
Igor Jerković Marina Rajić Zvonimir Marijanović Mate Bilić Stela Jokić 《分离科学与技术》2016,51(18):2925-2931
Supercritical (SC) CO2 extraction of dried Immortelle flowers was performed at different process parameters. The optimal extraction conditions related to the yield were determined by response surface methodology (yield 4.09% at 20 MPa and 52°C). The extracts were analyzed by GC-MS and tremetone derivatives dominated: bitalin A, 12-acetoxytremetone, gnaphaliol, 1-[2-(2-methyl-2,3-dihydroxypropyl)-2,3-dihydro-1-benzofuran-5-yl]ethanone, isobutyl bitalin A, and 1-[2-(acetylprop-1-en-2-yl)-3-hydroxy-2,3-dihydro-1-benzofuran-5-yl]ethanone. Striking differences were found among the essential oil and SC-CO2 extracts composition. The major oil compounds were γ-curcumene, α-pinene, β-selinene, α-selinene, and limonene. Mono- and sesquiterpene were found among minor constituents of the extracts. Neryl acetate was present in the extracts and essential oil. 相似文献
98.
Kamilla Soares de Mendonça João Renato de Jesus Junqueira Michel Cardoso de Angelis Pereira Marina Barbosa Vilela 《Drying Technology》2016,34(4):386-394
Osmotic dehydration assisted by ultrasound (ODAU) at low temperatures reduces water activity (aw) and maintains nutrients. The influence of solution concentration (SC; 20 to 60° Brix, xylitol and sorbitol) and ultrasound application time (tus, 0 to 40 min) in ODAU of yacon was studied with the aid of a response surface method. The optimum condition with respect to mass transfer parameters, aw, and fructan retention was SC of 60° Brix for both solutions and tus of 2.67 min for xylitol samples and 0 min for sorbitol samples. The application of ultrasound improved dehydration but resulted in depolymerization of fructans. 相似文献
99.
Optimization of the application of the Fenton chemistry for the remediation of a contaminated soil with polycyclic aromatic hydrocarbons 总被引:1,自引:0,他引:1 下载免费PDF全文
100.