全文获取类型
收费全文 | 4650篇 |
免费 | 582篇 |
国内免费 | 115篇 |
专业分类
电工技术 | 29篇 |
综合类 | 155篇 |
化学工业 | 1083篇 |
金属工艺 | 66篇 |
机械仪表 | 65篇 |
建筑科学 | 48篇 |
矿业工程 | 32篇 |
能源动力 | 65篇 |
轻工业 | 3215篇 |
水利工程 | 20篇 |
石油天然气 | 48篇 |
武器工业 | 4篇 |
无线电 | 96篇 |
一般工业技术 | 151篇 |
冶金工业 | 72篇 |
原子能技术 | 42篇 |
自动化技术 | 156篇 |
出版年
2024年 | 54篇 |
2023年 | 131篇 |
2022年 | 229篇 |
2021年 | 261篇 |
2020年 | 236篇 |
2019年 | 252篇 |
2018年 | 236篇 |
2017年 | 254篇 |
2016年 | 205篇 |
2015年 | 215篇 |
2014年 | 242篇 |
2013年 | 289篇 |
2012年 | 346篇 |
2011年 | 362篇 |
2010年 | 208篇 |
2009年 | 204篇 |
2008年 | 163篇 |
2007年 | 207篇 |
2006年 | 190篇 |
2005年 | 154篇 |
2004年 | 122篇 |
2003年 | 147篇 |
2002年 | 92篇 |
2001年 | 71篇 |
2000年 | 62篇 |
1999年 | 49篇 |
1998年 | 55篇 |
1997年 | 42篇 |
1996年 | 42篇 |
1995年 | 40篇 |
1994年 | 32篇 |
1993年 | 19篇 |
1992年 | 28篇 |
1991年 | 24篇 |
1990年 | 31篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有5347条查询结果,搜索用时 15 毫秒
21.
22.
以0.5 mm×3.0 mm碳棒为载体,氯化钯为前体,103Pd为放射性示踪剂,水合肼为还原剂,研究了化学沉积103Pd工艺。结果表明,化学沉积103Pd的优化条件为:2 g/L PdCl2、65 g/L Na2EDTA、700 mL/L 25%NH3•H2O、100 mL/L 5%H4N2•H2O,pH=10,时间90 min,温度50 ℃。化学沉积103Pd溶液稳定性好,反应易进行;有95%的103Pd沉积到载体棒上,碳棒对103Pd的吸收仅约为12%,103Pd利用率高;沉积层呈灰白色,表面平整;化学沉积103Pd批内均匀性好,重复性好。化学沉积103Pd技术可用于制备103Pd粒子和新型103Pd-125I复合粒子。 相似文献
23.
超声波提取葡萄籽油工艺的研究 总被引:13,自引:0,他引:13
介绍了超声波提取葡萄籽油的工艺,研究了萃取溶剂、超声波功率、超声时间、料液比、循环泵转速对提取率的影响.结果表明,最佳提取溶剂为石油醚,最佳工艺为:超声时间25 min,超声波功率500 W,循环泵转速1 200 r/min,料液比1∶15,在此条件下提取率达到94.12%. 相似文献
24.
精炼吊瓜籽油的脂肪酸分析 总被引:1,自引:0,他引:1
对压榨吊瓜籽毛油进行了精炼,计算出得率为54%。采用GC分析、比较了吊瓜籽精油、橄榄油和菜籽油的脂肪酸组分,表明吊瓜籽油中油酸、亚油酸含量为8.48%、33.6%,亚油酸含量高于橄榄油(8.48%)和菜籽油(13.03%).经过GC-MS确证,吊瓜籽含有丰富的角鲨烯(22.7%),是营养保健物质的新型来源. 相似文献
25.
Tumor detection in T1, T2, FLAIR and MPR brain images using a combination of optimization and fuzzy clustering improved by seed‐based region growing algorithm 下载免费PDF全文
G. Vishnuvarthanan M. Pallikonda Rajasekaran N. Anitha Vishnuvarthanan T. Arun Prasath M. Kannan 《International journal of imaging systems and technology》2017,27(1):33-45
Tumor and Edema region present in Magnetic Resonance (MR) brain image can be segmented using Optimization and Clustering merged with seed‐based region growing algorithm. The proposed algorithm shows effectiveness in tumor detection in T1 ‐ w, T2 – w, Fluid Attenuated Inversion Recovery and Multiplanar Reconstruction type MR brain images. After an initial level segmentation exhibited by Modified Particle Swarm Optimization (MPSO) and Fuzzy C – Means (FCM) algorithm, the seed points are initialized using the region growing algorithm and based on these seed points; tumor detection in MR brain images is done. The parameters taken for comparison with the conventional techniques are Mean Square Error, Peak Signal to Noise Ratio, Jaccard (Tanimoto) index, Dice Overlap indices and Computational Time. These parameters prove the efficacy of the proposed algorithm. Heterogeneous type tumor regions present in the input MR brain images are segmented using the proposed algorithm. Furthermore, the algorithm shows augmentation in the process of brain tumor identification. Availability of gold standard images has led to the comparison of the suggested algorithm with MPSO‐based FCM and conventional Region Growing algorithm. Also, the algorithm recommended through this research is capable of producing Similarity Index value of 0.96, Overlap Fraction value of 0.97 and Extra Fraction value of 0.05, which are far better than the values articulated by MPSO‐based FCM and Region Growing algorithm. The proposed algorithm favors the segmentation of contrast enhanced images. © 2017 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 27, 33–45, 2017 相似文献
26.
Nanta Janpitak Woraphon Lilakiatsakun Chanboon Sathitwiriyawong 《Information Security Journal: A Global Perspective》2020,29(4):169-182
ABSTRACTRecently, cryptocurrencies such as Bitcoin, Ethereum, etc, have rapidly been recognized as an asset, often called a digital asset. Comparing to the real assets, it would be handled carefully due to its own characteristics that are completely different. The disadvantage of such digital assets, on the one hand, is that whoever knows the private key of the wallet, they can easily take over that digital asset. On the other hand, if the wallet’s owners are dead without passing credential information to others, that asset will be lost forever. We thus propose the novel secure testament methodology for a digital asset such as Bitcoin to solve the mentioned problems. The mechanism is based on managing the mnemonic seed of the wallet so that an inheritor will obtain the mnemonic seed in a secure way. Two mechanisms of the proposed methodology are implemented. The first is to save the mnemonic seed in a secure repository. Therefore, no one can access to the cryptocurrency wallet while the owner still being alive and does not wish anybody to access. The second is to deliver the mnemonic seed securely to legitimate inheritor when the owner is suspected to be dead or disappeared. Finally, based on our experiment, the results show that the aforementioned problems can be solved. Furthermore, the proposed mechanism can help the owner of the asset to managing the confidentiality of their assets. 相似文献
27.
Pia Stari
Jure Mravlje Miran Mozeti
Rok Zaplotnik Barbara etina Bati
Ita Junkar Katarina Vogel Miku 《International journal of molecular sciences》2022,23(13)
Cold plasma (CP) technology is a technique used to change chemical and morphological characteristics of the surface of various materials. It is a newly emerging technology in agriculture used for seed treatment with the potential of improving seed germination and yield of crops. Wheat seeds were treated with glow (direct) or afterglow (indirect) low-pressure radio-frequency oxygen plasma. Chemical characteristics of the seed surface were evaluated by XPS and FTIR analysis, changes in the morphology of the seed pericarp were analysed by SEM and AFM, and physiological characteristics of the seedlings were determined by germination tests, growth studies, and the evaluation of α-amylase activity. Changes in seed wettability were also studied, mainly in correlation with functionalization of the seed surface and oxidation of lipid molecules. Only prolonged direct CP treatment resulted in altered morphology of the seed pericarp and increased its roughness. The degree of functionalization is more evident in direct compared to indirect CP treatment. CP treatment slowed the germination of seedlings, decreased the activity of α-amylase in seeds after imbibition, and affected the root system of seedlings. 相似文献
28.
Jean-Baptiste Domergue Julie Lalande Daniel Beucher Pascale Satour Cyril Abadie Anis M. Limami Guillaume Tcherkez 《International journal of molecular sciences》2022,23(15)
Seed size is often considered to be an important trait for seed quality, i.e., vigour and germination performance. It is believed that seed size reflects the quantity of reserve material and thus the C and N sources available for post-germinative processes. However, mechanisms linking seed size and quality are poorly documented. In particular, specific metabolic changes when seed size varies are not well-known. To gain insight into this aspect, we examined seed size and composition across different accessions of barrel medic (Medicago truncatula Gaertn.) from the genetic core collection. We conducted multi-elemental analyses and isotope measurements, as well as exact mass GC–MS metabolomics. There was a systematic increase in N content (+0.17% N mg−1) and a decrease in H content (–0.14% H mg−1) with seed size, reflecting lower lipid and higher S-poor protein quantity. There was also a decrease in 2H natural abundance (δ2H), due to the lower prevalence of 2H-enriched lipid hydrogen atoms that underwent isotopic exchange with water during seed development. Metabolomics showed that seed size correlates with free amino acid and hexoses content, and anticorrelates with amino acid degradation products, disaccharides, malic acid and free fatty acids. All accessions followed the same trend, with insignificant differences in metabolic properties between them. Our results show that there is no general, proportional increase in metabolite pools with seed size. Seed size appears to be determined by metabolic balance (between sugar and amino acid degradation vs. utilisation for storage), which is in turn likely determined by phloem source metabolite delivery during seed development. 相似文献
29.
Alexandre Garcia Jérôme Polesel‐Maris Pascal Viel Serge Palacin Thomas Berthelot 《Advanced functional materials》2011,21(11):2096-2102
The “ligand induced electroless plating (LIEP) process” is a simple process to obtain localized metal plating onto flexible polymers such as poly(ethylene terephtalate) and polyvinylidene fluoride sheets. This generic and cost‐effective process, efficient on any common polymer surface, is based on the covalent grafting by the GraftFast process of a thin chelating polymer film, such as poly(acrylic acid), which can complex copper ions. The entrapped copper ions are then chemically reduced in situ and the resulting Cu0 species act as a seed layer for the electroless copper growth which, thus, starts inside the host polymer. The present work focuses on the application of the LIEP process to the patterning of localized metallic tracks via two simple lithographic methods. The first is based on a standard photolithography process using a positive photoresist masking to prevent the covalent grafting of PAA in designated areas of the polymer substrate. In the second, the patterning is performed by direct printing of the mask with a commercial laser printer. In both cases, the mask was lifted off before the copper electroless plating step, which provides ecological benefits, since only the amount of copper necessary for the metallic patterning is used. 相似文献
30.
斯托克斯光种子法固体相干反斯托克斯拉曼频移器的理论研究 总被引:1,自引:0,他引:1
以波动方程和受激拉曼散射(SRS)物质方程为基础,采用光种子法,建立了固体相干反斯托克斯拉曼频移器的归一化耦合波方程,研究了晶体中反斯托克斯光转换效率。在脉冲抽运条件下分析了归一化增益系数G、归一化相位失配系数ΔK以及一阶斯托克斯光种子的归一化光场振幅ψs0三个变量对固体相干反斯托克斯拉曼频移器的影响,并作出了一系列相应曲线,由所得曲线估算了各归一化变量的合理取值范围。分析结果表明,在ΔK=0时,通过增大sψ0来打破拉曼增益抑制的影响,其转换效率峰值可达到44%。而当sψ0较弱时,可选取合适的相位失配系数,反斯托克斯光转换效率可达40%。 相似文献