全文获取类型
收费全文 | 19761篇 |
免费 | 2149篇 |
国内免费 | 1191篇 |
专业分类
电工技术 | 578篇 |
技术理论 | 1篇 |
综合类 | 1967篇 |
化学工业 | 2403篇 |
金属工艺 | 822篇 |
机械仪表 | 1325篇 |
建筑科学 | 4478篇 |
矿业工程 | 703篇 |
能源动力 | 470篇 |
轻工业 | 1251篇 |
水利工程 | 575篇 |
石油天然气 | 1615篇 |
武器工业 | 181篇 |
无线电 | 880篇 |
一般工业技术 | 3214篇 |
冶金工业 | 809篇 |
原子能技术 | 126篇 |
自动化技术 | 1703篇 |
出版年
2024年 | 164篇 |
2023年 | 415篇 |
2022年 | 642篇 |
2021年 | 714篇 |
2020年 | 767篇 |
2019年 | 668篇 |
2018年 | 598篇 |
2017年 | 669篇 |
2016年 | 677篇 |
2015年 | 734篇 |
2014年 | 1076篇 |
2013年 | 1309篇 |
2012年 | 1328篇 |
2011年 | 1348篇 |
2010年 | 1065篇 |
2009年 | 1109篇 |
2008年 | 1010篇 |
2007年 | 1270篇 |
2006年 | 1067篇 |
2005年 | 887篇 |
2004年 | 845篇 |
2003年 | 673篇 |
2002年 | 541篇 |
2001年 | 537篇 |
2000年 | 506篇 |
1999年 | 376篇 |
1998年 | 322篇 |
1997年 | 329篇 |
1996年 | 256篇 |
1995年 | 206篇 |
1994年 | 150篇 |
1993年 | 138篇 |
1992年 | 114篇 |
1991年 | 82篇 |
1990年 | 78篇 |
1989年 | 102篇 |
1988年 | 54篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 57篇 |
1984年 | 42篇 |
1983年 | 39篇 |
1982年 | 30篇 |
1981年 | 4篇 |
1980年 | 18篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1964年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Maysa T. Resende Charles Linder Zeev Wiesman 《Journal of the American Oil Chemists' Society》2020,97(12):1283-1297
Omega-3 polyunsaturated fatty acid (PUFA)-rich linseed oil (LSO) is an important component in biological systems, foods, and many other industrial products. In recent years, LSO has attracted increased attention in the field of functional foods, which has highlighted its facile susceptibility to aging by autoxidation. Common colorimetric and a long list of spectral methodologies have been used to follow after and predict LSO shelf life's quality, especially in regards to aging by autoxidation. These standard methodologies are nevertheless limited, because of the complexity of the LSO's chemical and physical changes. The goal of the present study is to develop a sensorial 1H LF-NMR energy relaxation time application based on monitoring primary chemical and structural changes occurring with time and temperature during oxidative thermal stress for better and rapid evaluation of LSO's aging process. Using 1H low-field NMR, the different T2 times of energy relaxations due to spin–spin coupling, and proton motion/mobility of LSO molecular segments were monitored. As previously reported, we characterized the chemical and structural changes in all phases of the autoxidation aging process. Starting from the initiation phase (abstraction of hydrogen radical, fatty acid chain rearrangement, and oxygen uptake yielding hydroperoxides products), through to the propagation phase (chain reactions resulting in tail cleavage to form alkoxy radicals, and alpha, beta-unsaturated aldehydes formation), and a termination phase (cross linking and production of polymerization end products). The 1H LF NMR transverse relaxation approach, monitors both the covalent bond's strong forces (100–400 kJ mol−1) in LSO oxidative aging decomposition, as well as secondary relatively weak interactive forces by hydrogen bonds (~70 kJ mol−1), and electrostatic bonds (0–50 kJ mol−1) contributing to secondary crosslinking interactions leading to a LSO viscous gel of polymerized products in the termination phase. In the present paper, we show that LSO tail segments mobility in terms of T2 multi-exponential energy relaxation time decays, generated by data reconstruction of 1H transverse relaxation components are providing a clear, sharp, and informative understanding of LSO sample's autoxidation aging processes. To support T2 time domain data analysis, we used data from high-field band-selective 1H NMR pulse excitation for quantification of hydroperoxides and aldehydes of the same LSO samples treated under the same thermal conditions (25, 40, 60, 80, 100, 120 °C) with pumped air for 168 hours. Peroxide value, viscosity, and self-diffusion analyses, as well as fatty acids profile and by-products determined by GC–MS on the same samples were carried out, and correlated with the LSO tail T2 energy relaxation time results. From these results, it is postulated that selective determination of LSO tail T2 time domain can be used as a rapid evaluation marker for following omega-3 PUFA-rich oils oxidative aging process within industrial and commercial products. 相似文献
912.
913.
Dibakar Sarkar Dr. Ipsita Chakraborty Marcello Condorelli Baijayanti Ghosh Thorben Mass Dr. Markus Weingarth Dr. Atin K Mandal Prof. Carmelo La Rosa Dr. Vivekanandan Subramanian Dr. Anirban Bhunia 《ChemMedChem》2020,15(3):293-301
The three GxxxG repeating motifs from the C-terminal region of β-amyloid (Aβ) peptide play a significant role in regulating the aggregation kinetics of the peptide. Mutation of these glycine residues to leucine greatly accelerates the fibrillation process but generates a varied toxicity profile. Using an array of biophysical techniques, we demonstrated the uniqueness of the composite glycine residues in these structural repeats. We used solvent relaxation NMR spectroscopy to investigate the role played by the surrounding water molecules in determining the corresponding aggregation pathway. Notably, the conformational changes induced by Gly33 and Gly37 mutations result in significantly decreased toxicity in a neuronal cell line. Our results indicate that G33xxxG37 is the primary motif responsible for Aβ neurotoxicity, hence providing a direct structure–function correlation. Targeting this motif, therefore, can be a promising strategy to prevent neuronal cell death associated with Alzheimer's and other related diseases, such as type II diabetes and Parkinson's. 相似文献
914.
915.
随着煤炭开采逐渐向深部转移,巷道围岩变形越来越严重。分析了深埋巷道围岩变形及支护技术,对研究巷道进行了三轴抗拉试验,得到煤和岩石力学参数,采用结构梁和弹性力学分析了巷道围岩变形,为模型分析提供了理论基础,然后采用FLAC^3D数值模拟软件,分析了巷道变形位移,与现场实测相比,数值模拟能够较好地模拟煤矿巷道实际变形情况。研究能够为巷道参数设计提供借鉴。 相似文献
916.
木里煤田是青海省重要的煤产地,其中聚乎更、哆嗦公马、雪霍立、外力哈达、热水等地含煤地层出露较好、煤系埋深较浅。受祁连山构造带以及阿尔金断裂走滑作用的控制,木里煤田构造类型多样。根据木里煤田的地质背景,从沉积聚煤规律、构造特征及其控煤作用等方面对木里煤田隐伏区及逆冲推覆构造下含煤地层进行分析,指出应在已知矿区外围逆冲推覆断层下盘找煤,同时被新生代覆盖的隐伏区为今后找煤的方向。 相似文献
917.
918.
研究立足新型领导风格探索影响煤矿企业员工安全行为的路径,构建教练型领导、员工幸福感与安全行为关系理论模型。首先,界定教练型领导和安全行为2个变量,明晰员工幸福感包含生活幸福感、工作幸福感和心理幸福感3个维度;然后用问卷调查法采集数据,利用结构方程模型和Bootstrap检验法分析数据,实证检验了煤矿企业教练型领导与安全行为的关系及员工幸福感的中介作用。结果表明:煤矿企业教练型领导对安全行为和员工幸福感的3个维度均存在显著的正向影响,员工幸福感在教练型领导对安全行为的影响中起中介作用,且工作幸福感的中介效用最显著。具体而言,煤矿企业教练型领导行为的作用水平越高,会诱发员工高幸福感,员工的安全行为表现越好。 相似文献
919.
920.
用固相反应法制备了BaTi1-xSnxO3(0.15≤x≤0.30)系铁电陶瓷.研究了它们的介电常数与温度和频率的关系,发现BaTi1-xSnxO3经历了一个由单纯相变弥散铁电体到弛豫型铁电体的变化过程.数据分析表明,BaTi1-xSnxO3系铁电材料是否出现介电弛豫与最大介电常数值对应的温度Tm以上一段温度区间内的介电弥散程度存在对应关系.研究还发现,将交变测量电压由1 Vrms提高到20 Vrms时,可以使BaTi1-xSnxO3陶瓷的Tm向低温方向移动. 相似文献