全文获取类型
收费全文 | 272760篇 |
免费 | 3420篇 |
国内免费 | 1277篇 |
专业分类
电工技术 | 4700篇 |
综合类 | 514篇 |
化学工业 | 37605篇 |
金属工艺 | 11045篇 |
机械仪表 | 8215篇 |
建筑科学 | 6166篇 |
矿业工程 | 1573篇 |
能源动力 | 6867篇 |
轻工业 | 21989篇 |
水利工程 | 3016篇 |
石油天然气 | 5771篇 |
武器工业 | 43篇 |
无线电 | 33217篇 |
一般工业技术 | 55744篇 |
冶金工业 | 50873篇 |
原子能技术 | 7481篇 |
自动化技术 | 22638篇 |
出版年
2021年 | 1922篇 |
2019年 | 2051篇 |
2018年 | 3559篇 |
2017年 | 3664篇 |
2016年 | 3823篇 |
2015年 | 2391篇 |
2014年 | 4258篇 |
2013年 | 11870篇 |
2012年 | 6984篇 |
2011年 | 9617篇 |
2010年 | 7428篇 |
2009年 | 8677篇 |
2008年 | 9022篇 |
2007年 | 9082篇 |
2006年 | 7761篇 |
2005年 | 7198篇 |
2004年 | 7139篇 |
2003年 | 6894篇 |
2002年 | 6412篇 |
2001年 | 6521篇 |
2000年 | 6042篇 |
1999年 | 6425篇 |
1998年 | 15982篇 |
1997年 | 11303篇 |
1996年 | 8581篇 |
1995年 | 6797篇 |
1994年 | 5956篇 |
1993年 | 6007篇 |
1992年 | 4361篇 |
1991年 | 4144篇 |
1990年 | 4044篇 |
1989年 | 3997篇 |
1988年 | 3706篇 |
1987年 | 3343篇 |
1986年 | 3352篇 |
1985年 | 3695篇 |
1984年 | 3430篇 |
1983年 | 3181篇 |
1982年 | 3002篇 |
1981年 | 3008篇 |
1980年 | 2997篇 |
1979年 | 2802篇 |
1978年 | 2845篇 |
1977年 | 3120篇 |
1976年 | 4075篇 |
1975年 | 2407篇 |
1974年 | 2366篇 |
1973年 | 2377篇 |
1972年 | 2010篇 |
1971年 | 1768篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Peter K. Windsor Stephen P. Plassmeyer Dominic S. Mattock Jonathan C. Bradfield Erika Y. Choi Bill R. Miller III Byung Hee Han 《International journal of molecular sciences》2021,22(6)
Deposition of amyloid β (Aβ) fibrils in the brain is a key pathologic hallmark of Alzheimer’s disease. A class of polyphenolic biflavonoids is known to have anti-amyloidogenic effects by inhibiting aggregation of Aβ and promoting disaggregation of Aβ fibrils. In the present study, we further sought to investigate the structural basis of the Aβ disaggregating activity of biflavonoids and their interactions at the atomic level. A thioflavin T (ThT) fluorescence assay revealed that amentoflavone-type biflavonoids promote disaggregation of Aβ fibrils with varying potency due to specific structural differences. The computational analysis herein provides the first atomistic details for the mechanism of Aβ disaggregation by biflavonoids. Molecular docking analysis showed that biflavonoids preferentially bind to the aromatic-rich, partially ordered N-termini of Aβ fibril via the π–π interactions. Moreover, docking scores correlate well with the ThT EC50 values. Molecular dynamic simulations revealed that biflavonoids decrease the content of β-sheet in Aβ fibril in a structure-dependent manner. Hydrogen bond analysis further supported that the substitution of hydroxyl groups capable of hydrogen bond formation at two positions on the biflavonoid scaffold leads to significantly disaggregation of Aβ fibrils. Taken together, our data indicate that biflavonoids promote disaggregation of Aβ fibrils due to their ability to disrupt the fibril structure, suggesting biflavonoids as a lead class of compounds to develop a therapeutic agent for Alzheimer’s disease. 相似文献
2.
Raquel Cano Jos L. Prez Liss Angarita Dvila ngel Ortega Yosselin Gmez Nereida Josefina Valero-Cedeo Heliana Parra Alexander Manzano Teresa Isabel Vliz Castro María P. Díaz Albornoz Gabriel Cano Joselyn Rojas-Quintero Maricarmen Chacín Valmore Bermúdez 《International journal of molecular sciences》2021,22(9)
Non-alcoholic fatty liver disease (NAFLD) is considered the most common liver disorder, affecting around 25% of the population worldwide. It is a complex disease spectrum, closely linked with other conditions such as obesity, insulin resistance, type 2 diabetes mellitus, and metabolic syndrome, which may increase liver-related mortality. In light of this, numerous efforts have been carried out in recent years in order to clarify its pathogenesis and create new prevention strategies. Currently, the essential role of environmental pollutants in NAFLD development is recognized. Particularly, endocrine-disrupting chemicals (EDCs) have a notable influence. EDCs can be classified as natural (phytoestrogens, genistein, and coumestrol) or synthetic, and the latter ones can be further subdivided into industrial (dioxins, polychlorinated biphenyls, and alkylphenols), agricultural (pesticides, insecticides, herbicides, and fungicides), residential (phthalates, polybrominated biphenyls, and bisphenol A), and pharmaceutical (parabens). Several experimental models have proposed a mechanism involving this group of substances with the disruption of hepatic metabolism, which promotes NAFLD. These include an imbalance between lipid influx/efflux in the liver, mitochondrial dysfunction, liver inflammation, and epigenetic reprogramming. It can be concluded that exposure to EDCs might play a crucial role in NAFLD initiation and evolution. However, further investigations supporting these effects in humans are required. 相似文献
3.
4.
Patil Rupesh C. Jagdale Ashutosh A. Patil Uttam P. Ghodake Jeevan S. Mali Sawanta S. Hong Chang K. Patil Suresh S. 《Catalysis Letters》2021,151(12):3617-3631
Catalysis Letters - We converted agro-waste Custard Apple Peels (CAP) to ash via thermal treatment, on which Pd(OAc)2 was immobilized easily that produced a low-cost, highly efficient Pd/CAP-ash... 相似文献
5.
6.
Minh Nguyen Vo Jonathan P. Ruffley J. Karl Johnson 《American Institute of Chemical Engineers》2021,67(3):e17156
Metal organic frameworks (MOFs) containing zirconium secondary building units (SBUs) in UiO-67 and related MOFs, are highly active for neutralizing both the chemical warfare agents and simulants, such as dimethyl methylphosphonate (DMMP). However, two recent publications gave conflicting reports of DMMP reaction with UiO-67 under ultra high vacuum (UHV) conditions, with one reporting chemisorption and reaction (Wang et al., J Phys Chem C, 2017, 121, 11261–11272) and the other reporting only physisorption and reversible desorption (Ruffley et al., J Phys Chem C, 2019, 123, 19748–19758) from very similar temperature programmed desorption experiments. We show that the discrepancy between these experiments may be explained by different levels of missing linker defects in the UiO-67 samples. We present density functional theory calculations showing that SBU sites having two-adjacent missing linkers exhibit reaction barriers that are about 30 kJ/mol lower than SBU sites having a single missing linker. We also show that topology of the undercoordinated sites plays an important role in the reaction barrier under UHV conditions. 相似文献
7.
Grachev S. P. Zhilyaev A. A. Laryukhin V. B. Novichkov D. E. Galuzin V. A. Simonova E. V. Maiyorov I. V. Skobelev P. O. 《Automation and Remote Control》2021,82(11):1857-1885
Automation and Remote Control - We give the statement of the real-time adaptive enterprise resource management problem and provide examples of contemporary adaptive resource management problems in... 相似文献
8.
Poletskov P. P. Nikitenko O. A. Kuznetsova A. S. Alekseev D. Yu. 《Metal Science and Heat Treatment》2021,63(3-4):171-177
Metal Science and Heat Treatment - The structure and mechanical properties of novel structural high-strength cold-resistant steel 20G2SMRA are studied after quenching and tempering at different... 相似文献
9.
Kaio C. S. Rodrigues Ivan I. K. Veloso Marcelo P. A. Ribeiro Antonio J. G. Cruz Alberto C. Badino 《加拿大化工杂志》2021,99(1):401-409
Fast, simple, accurate, and inexpensive methods for obtaining analyte concentration data are desirable in the industrial sector. In the present study, the use of Fourier transform mid‐infrared (FT‐MIR) spectroscopy, combined with partial least squares (PLS) regression, was investigated as a tool for real‐time monitoring of processes of ethanol absorption in glycols. Calibration was performed using simple synthetic samples containing ethanol, water, and monoethylene glycol (MEG) or diethylene glycol (DEG). The PLS models presented excellent performance, with correlation coefficients (R2) close to unity and root‐mean‐square errors of cross‐validation (RMSECV) and prediction (RMSEP) lower than 2% of the calibration data ranges for both analytes (ethanol and water) in both absorbents (MEG and DEG). The monitoring technique developed has potential to be applied in absorption processes and could also be used in other large‐scale unit operations, providing information in real time and enhancing process control. 相似文献
10.
E.N. Lysenko V.A. Vlasov A.V. Malyshev E.A. Sheveleva A.P. Surzhikov 《Ceramics International》2021,47(17):23935-23941
The effect of dry and wet ball milling of LiFe5O8 ferrite powder on the microstructure and electromagnetic properties of ferrite ceramics was studied using XRD analysis, scanning electron microscopy, dilatometry, thermogravimetry, calorimetry, and measurement of specific magnetization and electrical resistance. The sintering temperature was 1050 °C; the sintering time was 2 h. It was found that ferrite fabricated from dry-milled powder exhibits an ordered α-LiFe5O8 phase with bulk density of 91%. Its saturation magnetization and Curie temperature are 55 emu/g and 628°С, respectively. Specific electrical resistance is 4?106 Ω cm. Wet milling in isopropyl alcohol causes formation of a disordered β-LiFe5O8 phase. Ceramics produced by this method shows higher bulk density (97%) and low porosity, and an order of magnitude lower resistivity. Its saturation magnetization and Curie temperature are 51 emu/g and 607°С, respectively. 相似文献