首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1186篇
  免费   65篇
电工技术   13篇
综合类   1篇
化学工业   402篇
金属工艺   8篇
机械仪表   24篇
建筑科学   70篇
能源动力   62篇
轻工业   209篇
水利工程   2篇
石油天然气   1篇
无线电   67篇
一般工业技术   165篇
冶金工业   23篇
原子能技术   6篇
自动化技术   198篇
  2024年   1篇
  2023年   19篇
  2022年   75篇
  2021年   77篇
  2020年   39篇
  2019年   34篇
  2018年   45篇
  2017年   32篇
  2016年   52篇
  2015年   50篇
  2014年   51篇
  2013年   87篇
  2012年   70篇
  2011年   85篇
  2010年   79篇
  2009年   75篇
  2008年   53篇
  2007年   55篇
  2006年   38篇
  2005年   37篇
  2004年   34篇
  2003年   28篇
  2002年   17篇
  2001年   6篇
  2000年   7篇
  1999年   11篇
  1998年   15篇
  1997年   5篇
  1996年   6篇
  1995年   3篇
  1994年   8篇
  1993年   4篇
  1992年   6篇
  1991年   4篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1987年   3篇
  1985年   6篇
  1984年   6篇
  1983年   3篇
  1982年   3篇
  1981年   1篇
  1980年   5篇
  1979年   2篇
  1977年   2篇
  1975年   1篇
  1973年   1篇
  1971年   1篇
  1964年   1篇
排序方式: 共有1251条查询结果,搜索用时 15 毫秒
991.
The performance of CeO2-supported Pt–Ni and Pt–Co catalysts in the low temperature-Ethanol Steam Reforming (ESR) reaction has been evaluated studying the effect of the preparation method (impregnation/coprecipitation) and parameters such as dilution ratio, temperature, water-to-ethanol feed ratio and Gas Hourly Space Velocity (GHSV). The results show that impregnated samples perform better. In particular, the Pt/Ni/CeO2 catalyst starting from 350 °C leads to a products distribution very close to the equilibrium calculations, with a low CO content that is ideal for fuel cells devices. In addition, the Co-based catalysts appear attractive in terms of hydrogen yield and coking tendency.  相似文献   
992.
Osteosarcopenia (OS) is defined by the concurrent presence of osteopenia/osteoporosis and sarcopenia. The pathogenesis and etiology of OS involve genetic, biochemical, mechanical, and lifestyle factors. Moreover, an inadequate nutritional status, such as low intake of protein, vitamin D, and calcium, and a reduction in physical activity are key risk factors for OS. This review aims to increase knowledge about diagnosis, incidence, etiology, and treatment of OS through clinical studies that treat OS as a single disease. Clinical studies show the relationship between OS and the risk of frailty, falls, and fractures and some association with Non-communicable diseases (NCDs) pathologies such as diabetes, obesity, and cardiovascular disease. In some cases, the importance of deepening the related mechanisms is emphasized. Physical exercise with adequate nutrition and nutritional supplementations such as proteins, Vitamin D, or calcium, represent a significant strategy for breaking OS. In addition, pharmacological interventions may confer benefits on muscle and bone health. Both non-pharmacological and pharmacological interventions require additional randomized controlled trials (RCT) in humans to deepen the synergistic effect of exercise, nutritional interventions, and drug compounds in osteosarcopenia.  相似文献   
993.
Anthocyanins are natural dietary pigments that could be involved in various health effects. However their mechanisms of absorption are still not fully understood. The aim of this study was to evaluate the influence of glucose on anthocyanin absorption in rats. We first studied anthocyanin bioavailability in rats that received by gastric intubation approximately 53 micromol cyanidin 3-glucoside (Cy 3-glc) equivalents from a red orange extract with or without 2.51 mmol glucose. Neither 24-h urinary anthocyanin excretion nor plasma anthocyanin concentration was significantly affected by simultaneous ingestion of glucose. The influence of glucose (12, 42 or 72 mM) on intestinal absorption of Cy 3-glc (pure or from a red orange extract; approximately 12.3 microM) was further studied using an in situ intestinal perfusion model. Absorption of pure Cy 3-glc from the intestinal lumen was not significantly affected by the amount of glucose. However, intestinal absorption of Cy 3-glc from the red orange extract (6.49 +/- 1.44%, n = 6) was significantly less than that of pure Cy 3-glc (17.5 +/- 1.3%, n = 7) (p < 0.01) suggesting that the red orange extract contained other components that were able to interfere with Cy 3-glc intestinal absorption. This study has thus shown that glucose did not interfere with anthocyanin glucoside absorption.  相似文献   
994.
995.
Atypical Spitz tumors (AST) deviate from stereotypical Spitz nevi for one or more atypical features and are now regarded as an intermediate category of melanocytic tumors with uncertain malignant potential. Activating NTRK1/NTRK3 fusions elicit oncogenic events in Spitz lesions and are targetable with kinase inhibitors. However, their prevalence among ASTs and the optimal approach for their detection is yet to be determined. A series of 180 ASTs were screened with pan-TRK immunohistochemistry and the presence of NTRK fusions was confirmed using FISH, two different RNA-based NGS panels for solid tumors, and a specific real time RT-PCR panel. Overall, 26 ASTs showed pan-TRK immunostaining. NTRK1 fusions were detected in 15 of these cases showing cytoplasmic immunoreaction, whereas NTRK3 was detected in one case showing nuclear immunoreaction. Molecular tests resulted all positive in only two ASTs (included the NTRK3 translocated), RNA-based NGS and real time RT-PCR were both positive in three cases, and FISH and real time RT-PCR in another two cases. In seven ASTs NTRK1 fusions were detected only by FISH and in two cases only by real time RT-PCR. The frequency of NTRK fusions in ASTs is 9%, with a clear prevalence of NTRK1 compared to NTRK3 alterations. Pan-TRK immunohistochemistry is an excellent screening test. Confirmation of NTRK fusions may require the use of different molecular techniques.  相似文献   
996.
This research focuses on the X-ray structure of 4,6-dichloro-5-nitrobenzofuroxan 1 and of some of its amino derivatives (4a, 4e, 4g, and 4l) and on DFT calculations concerning the nucleophilic reactivity of 1. We have found that by changing the solvent used for crystallization, it is possible to obtain 4,6-dichloro-5-nitrobenzofuroxan (1) in different polymorphic structures. Moreover, the different torsional angles observed for the nitro group in 1 and in its amino derivatives (4a, 4e, 4g, and 4l) are strictly dependent on the steric hindrance of the substituent at C-4. DFT calculations on the course of the nucleophilic substitution confirm the role of the condensed furoxan ring in altering the aromaticity of the carbocyclic frame, while chlorine atoms strongly influence the dihedral angle and the rotational barrier of the nitro group. These results corroborate previous observations based on experimental kinetic data and give a deep picture of the reaction with amines, which proceeds via a “non-aromatic” nucleophilic substitution.  相似文献   
997.
S100B is an astrocytic protein behaving at high concentration as a damage-associated molecular pattern molecule. A direct correlation between the increased amount of S100B and inflammatory processes has been demonstrated, and in particular, the inhibitor of S100B activity pentamidine has been shown to ameliorate clinical scores and neuropathologic-biomolecular parameters in the relapsing-remitting experimental autoimmune encephalomyelitis mouse model of multiple sclerosis. This study investigates the effect of arundic acid (AA), a known inhibitor of astrocytic S100B synthesis, in the chronic experimental autoimmune encephalomyelitis, which is another mouse model of multiple sclerosis usually studied. By the daily evaluation of clinical scores and neuropathologic-molecular analysis performed in the spinal cord, we observed that the AA-treated group showed lower severity compared to the vehicle-treated mice, particularly in the early phase of disease onset. We also observed a significant reduction of astrocytosis, demyelination, immune infiltrates, proinflammatory cytokines expression and enzymatic oxidative reactivity in the AA-treated group. Overall, our results reinforce the involvement of S100B in the development of animal models of multiple sclerosis and propose AA targeting the S100B protein as a focused potential drug to be considered for multiple sclerosis treatment.  相似文献   
998.
This paper deals with the internal finishing of tubular components made from a high strength aluminium alloy (AA 6082 T6) using a fluidized bed assisted abrasive jet machining (FB-AJM) system.Firstly, a Taguchi's experimental plan was used to investigate the influence of abrasive jet speed, machining cycle, and abrasive mesh size on surface roughness and material removal trends. Secondly, the leading finishing mechanisms were studied using combined 3d profilometer-SEM analysis to monitor the evolution of the surface morphology of machined workpieces. Finally, the circumferential uniformity and precision machining of the inner surface of workpieces were tested by evaluating the values of the more significant roughness parameters in different circumferential locations.Consistent trends of surface roughness vs. operational parameters were measured, and significant material removal was found to affect the workpieces during machining. As a result, FB-AJM was found to preferentially machine the asperities and irregularities of the surface, thereby altering the overall surface morphology producing more regular and smoother finishing. Moreover, the good circumferential uniformity and machining accuracy FB-AJM guarantees even on ductile aluminium alloy workpieces ensure that this technology can be applied to a diverse set of industrial components.  相似文献   
999.
Through differential scanning calorimetry, the crystallization kinetics of syndiotactic polypropylene (sPP) nanocomposites with organically modified layered silicates has been investigated in both nonisothermal and isothermal conditions. A strong influence on the thermal behavior is exerted by the compatibilizer agent (low molecular weight isotactic polypropylene‐g‐maleic anydrhyde, iPP‐g‐MA), which increases the crystallization rate of sPP. A further strong increase in the crystallization rate is observed upon increasing the OLS content in the sample. The kinetics data have been analyzed through the Ozawa, Avrami, and Tobin methods, the first of them resulted ineffective in describing our data. Morphological analyses have been performed by polarized optical microscopy and atomic force microscopy. Spherulitic morphology is observed for neat sPP; for the sample containing only the compatibilizer the spherulites grow around the iPP‐g‐MA particles, revealing their nucleating effect on sPP crystallization; for the nanocomposites the spherulitic morphology is lost: the texture appears globular, compact; inside the globules lamellae are present, parallel one to the other. POLYM. ENG. SCI., 46:1433–1442, 2006. © 2006 Society of Plastics Engineers  相似文献   
1000.
The lipid fraction of goat milk was subjected to transesterification using a commercially available immobilized lipase to decrease the amount of short- and medium-chain fatty acids (C4–C14) by enrichment of the reaction mixture with long-chain (C18:1 and C18:2) fatty acids. Aliquots were taken during, transesterification at different reaction times and analyzed for triglycerides and their fatty acid components. The gas chromatographic analyses of triglycerides (previously isolated by thinlayer chromatography) showed that at 6 h reaction under the experimental conditions led to the greatest reduction of the low molecular weight triglycerides (C22–C38) and concomitantly to the greatest increase in the higher molecular weight triglycerides (C48–C54). These changes correlated with the variations observed in the fatty acids of the triglyceride fraction.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号