全文获取类型
收费全文 | 3269篇 |
免费 | 347篇 |
国内免费 | 135篇 |
专业分类
电工技术 | 142篇 |
综合类 | 264篇 |
化学工业 | 680篇 |
金属工艺 | 158篇 |
机械仪表 | 183篇 |
建筑科学 | 249篇 |
矿业工程 | 70篇 |
能源动力 | 112篇 |
轻工业 | 227篇 |
水利工程 | 42篇 |
石油天然气 | 78篇 |
武器工业 | 12篇 |
无线电 | 345篇 |
一般工业技术 | 462篇 |
冶金工业 | 172篇 |
原子能技术 | 30篇 |
自动化技术 | 525篇 |
出版年
2024年 | 7篇 |
2023年 | 50篇 |
2022年 | 92篇 |
2021年 | 196篇 |
2020年 | 112篇 |
2019年 | 117篇 |
2018年 | 114篇 |
2017年 | 108篇 |
2016年 | 102篇 |
2015年 | 121篇 |
2014年 | 152篇 |
2013年 | 183篇 |
2012年 | 154篇 |
2011年 | 153篇 |
2010年 | 124篇 |
2009年 | 154篇 |
2008年 | 159篇 |
2007年 | 127篇 |
2006年 | 128篇 |
2005年 | 101篇 |
2004年 | 119篇 |
2003年 | 215篇 |
2002年 | 290篇 |
2001年 | 265篇 |
2000年 | 134篇 |
1999年 | 78篇 |
1998年 | 28篇 |
1997年 | 24篇 |
1996年 | 22篇 |
1995年 | 13篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1972年 | 1篇 |
1967年 | 3篇 |
1964年 | 1篇 |
排序方式: 共有3751条查询结果,搜索用时 15 毫秒
1.
Anna Stasiowicz Natalia Rosiak Ewa Tykarska Maciej Kozak Jacek Jenczyk Piotr Szulc Joanna Kobus-Cisowska Kornelia Lewandowska Anita Paziska Wojciech Paziski Judyta Cielecka-Piontek 《International journal of molecular sciences》2021,22(8)
Piperine is an alkaloid that has extensive pharmacological activity and impacts other active substances bioavailability due to inhibition of CYP450 enzymes, stimulation of amino acid transporters and P-glycoprotein inhibition. Low solubility and the associated low bioavailability of piperine limit its potential. The combination of piperine with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) causes a significant increase in its solubility and, consequently, an increase in permeability through gastrointestinal tract membranes and the blood–brain barrier. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) were used to characterize interactions between piperine and HP-β-CD. The observed physicochemical changes should be combined with the process of piperine and CD system formation. Importantly, with an increase in solubility and permeability of piperine as a result of interaction with CD, it was proven to maintain its biological activity concerning the antioxidant potential (2,2-diphenyl-1-picryl-hydrazyl-hydrate assay), inhibition of enzymes essential for the inflammatory process and for neurodegenerative changes (hyaluronidase, acetylcholinesterase, butyrylcholinesterase). 相似文献
2.
Fernanda Monedeiro Viorica Railean-Plugaru Maciej Monedeiro-Milanowski Pawe Pomastowski Bogusaw Buszewski 《International journal of molecular sciences》2021,22(9)
Considering the advent of antibiotic resistance, the study of bacterial metabolic behavior stimulated by novel antimicrobial agents becomes a relevant tool to elucidate involved adaptive pathways. Profiling of volatile metabolites was performed to monitor alterations of bacterial metabolism induced by biosynthesized silver nanoparticles (bio-AgNPs). Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae and Proteus mirabilis were isolated from pressure ulcers, and their cultures were prepared in the presence/absence of bio-AgNPs at 12.5, 25 and 50 µg mL−1. Headspace solid phase microextraction associated to gas chromatography–mass spectrometry was the employed analytical platform. At the lower concentration level, the agent promoted positive modulation of products of fermentation routes and bioactive volatiles, indicating an attempt of bacteria to adapt to an ongoing suppression of cellular respiration. Augmented response of aldehydes and other possible products of lipid oxidative cleavage was noticed for increasing levels of bio-AgNPs. The greatest concentration of agent caused a reduction of 44 to 80% in the variety of compounds found in the control samples. Pathway analysis indicated overall inhibition of amino acids and fatty acids routes. The present assessment may provide a deeper understanding of molecular mechanisms of bio-AgNPs and how the metabolic response of bacteria is untangled. 相似文献
3.
Effect of complexation of oxidised corn starch with mineral elements on physicochemical properties 下载免费PDF全文
Sławomir Pietrzyk Teresa Fortuna Lesław Juszczak Dorota Gałkowska Karolina Królikowska Karolina Zięba 《International Journal of Food Science & Technology》2015,50(4):934-941
The objective of this study was to determine the effect of complexation of oxidised starch with mineral elements on its physicochemical properties. Corn starch was oxidised with sodium hypochlorite and, afterwards, modified with ions of potassium, magnesium and iron. Thus, native and modified starches were analysed for: contents of mineral elements, colour parameters (L*a*b*), water binding capacity and solubility in water at temperature of 60 and 80 °C. Thermodynamic characteristics of gelatinisation by DSC, molecular weight distribution by GPC, intrinsic viscosity and pasting properties by RVA were studied. The efficiency of incorporation of metal ions into oxidised corn starch was about 30%, 20% and 20% for potassium, magnesium and iron ions, respectively. The complexation with potassium ions caused the greatest changes in the molecular weight distribution and the intrinsic viscosity of starches and viscosity of starch pastes. Only modification of starch with iron ions affected the colour parameters of the starch. Incorporation of metal ions into starch resulted also in changes in its water binding capacity and solubility in water. 相似文献
4.
针对辽河油田应用泡沫夹克管道的情况,从泡沫夹克管的制作和敷设施工直到设计等环节,结合泡沫夹克管防腐保温的机理,并从理论与实践相结合角度出发,提出导致泡沫夹克管腐蚀损坏的最主要原因是管道保温层漏水,进而提出了在设计和施工过程中提高泡沫夹克管质量的措施。 相似文献
5.
We consider relational structures such that is a set and are two binary relations on . For a number of different classes of structures we show that any structure can be represented as the intersection of its
maximal extensions. Such a property – called extension completeness – can be seen as a generalisation of Szpilrajn's theorem
which states that each partial order is the intersection of its total order extensions. When can be interpreted as causality and as ‘weak’ causality we obtain a model of concurrent histories generalising that based on causal partial orders.
Received 1 February 1994 / 6 May 1996 相似文献
6.
深亚微米MOSFET衬底电流的模拟与分析 总被引:1,自引:0,他引:1
利用器件模拟手段对深亚微米MOSFET的衬底电流进行了研究和分析,给出了有效的道长度,栅氧厚度,源漏结深,衬底掺杂浓度以及电源电压对深亚微米MOSFET衬底电流的影响,发现电源电压对深亚微米MOSFET的衬底电流有着强烈的影响,热载流子效应随电源电压的降低而迅速减小,当电源电压降低到一定程度时,热载流子效应不再成为影响深亚微米MOS电路可靠性的主要问题。 相似文献
7.
8.
9.
10.
单层球面网壳地震反应特征分析 总被引:29,自引:0,他引:29
考虑不同矢跨比、荷载、跨度和支座刚度等多种因素的影响,对单层球面网壳在地震作用下的反应进行了较全面的研究,给出了其随各参数变化的规律,得出了在单层球面网壳抗震设计中起控制作用的是水平地震作用而不是竖向地震作用等有益的结论.此外本文还给出了由于阻尼比不同而需对引用现行抗震规范反应谱分析的网壳地震作用进行修正的建议. 相似文献