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   39897篇
  免费   368篇
  国内免费   1054篇
电工技术   565篇
综合类   225篇
化学工业   3842篇
金属工艺   1270篇
机械仪表   2137篇
建筑科学   2249篇
矿业工程   1749篇
能源动力   228篇
轻工业   7795篇
水利工程   788篇
石油天然气   1032篇
武器工业   232篇
无线电   2413篇
一般工业技术   13153篇
冶金工业   772篇
原子能技术   394篇
自动化技术   2475篇
  2022年   70篇
  2021年   84篇
  2020年   65篇
  2018年   82篇
  2016年   76篇
  2015年   99篇
  2014年   192篇
  2013年   199篇
  2012年   3970篇
  2011年   4989篇
  2010年   1058篇
  2009年   491篇
  2008年   3346篇
  2007年   3171篇
  2006年   2710篇
  2005年   2344篇
  2004年   1961篇
  2003年   1640篇
  2002年   1557篇
  2001年   1262篇
  2000年   1253篇
  1999年   822篇
  1998年   551篇
  1997年   506篇
  1996年   506篇
  1995年   540篇
  1994年   443篇
  1993年   373篇
  1992年   501篇
  1991年   508篇
  1990年   457篇
  1989年   434篇
  1988年   410篇
  1987年   479篇
  1986年   481篇
  1985年   489篇
  1984年   471篇
  1983年   384篇
  1982年   396篇
  1981年   341篇
  1980年   276篇
  1979年   212篇
  1978年   131篇
  1977年   53篇
  1976年   71篇
  1975年   65篇
  1974年   64篇
  1973年   53篇
  1965年   80篇
  1964年   62篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The role of peroxisomal processes in the maintenance of neurons has not been thoroughly investigated. We propose using Caenorhabditis elegans as a model organism for studying the molecular basis underlying neurodegeneration in certain human peroxisomal disorders, e.g. Zellweger syndrome, since the nematode neural network is well characterized and relatively simple in function. Here we have identified C. elegans PEX-5 (C34C6.6) representing the receptor for peroxisomal targeting signal type 1 (PTS1), defective in patients with such disorders. PEX-5 interacted strongly in a two-hybrid assay with Gal4p-SKL, and a screen using PEX-5 identified interaction partners that were predominantly terminated with PTS1 or its variants. A list of C. elegans proteins with similarities to well-characterized yeast beta-oxidation enzymes was compiled by homology probing. The possible subcellular localization of these orthologues was predicted using an algorithm based on trafficking signals. Examining the C termini of selected nematode proteins for PTS1 function substantiated predictions made regarding the proteins' peroxisomal location. It is concluded that the eukaryotic PEX5-dependent route for importing PTS1-containing proteins into peroxisomes is conserved in nematodes. C. elegans might emerge as an attractive model system for studying the importance of peroxisomes and affiliated processes in neurodegeneration, and also for studying a beta-oxidation process that is potentially compartmentalized in both mitochondria and peroxisomes.  相似文献   
52.
在生产层特别是在致密含气砂岩中合理放置支撑剂是产量优化成功的关键。几十年来,油气行业一直采用同位素作为支撑剂标记来帮助确定支撑剂放置的是否成功。一般是在压裂的不同阶段加入放射性示踪剂,以帮助评价支撑剂放置在各目的层的放置情况。  相似文献   
53.
德国纺织机械与高性能材料技术研究所(ITM)开发出一种通过在人体内植入复杂的移植物治疗血管疾病的新技术.基于计算机辅助设计(CAD)技术,可对患者所需的移植物的结构数据进行流程化处理与定制,并在提花织机上进行一体化生产.与现有的缝制和制备工艺相比,应用该一体化制备技术制备定制型管状移植物具有较高的时间和成本效益.  相似文献   
54.
Tang D  Tang J  Li Q  Su B  Chen G 《Analytical chemistry》2011,83(19):7255-7259
This work reports an aptamer-based, disposable, and multiplexed sensing platform for simultaneous electrochemical determination of small molecules, employing adenosine triphosphate (ATP) and cocaine as the model target analytes. The multiplexed sensing strategy is based on target-induced release of distinguishable redox tag-conjugated aptamers from a magnetic graphene platform. The electronic signal of the aptasensors could be further amplified by coupling DNase I with catalytic recycling of self-produced reactants. The assay was based on the change in the current at the various peak potentials in the presence of the corresponding signal tags. Experimental results revealed that the multiplexed electrochemical aptasensor enabled the simultaneous monitoring of ATP and cocaine in a single run with wide working ranges and low detection limits (LODs: 0.1 pM for ATP and 1.5 pM for cocaine). This concept offers promise for rapid, simple, and cost-effective analysis of biological samples.  相似文献   
55.
In this study we prepared nanocarrier of erythropoietin (EPO) and the curative effect of the EPO-containing nanoparticles for periventricular leukomalacia (PVL) model was validated. It was demonstrated that EPO-containing nanoparticles can ameliorate drug-induced liquefaction caused by hypoxia. EPO-containing nanomedicine may open new therapeutic strategies in hypoxia cure.  相似文献   
56.
New optical configurations for performing general coordinate transformation operations of shear, rotation, and their combination are presented. These configurations consist of refractive spherical and cylindrical lenses that are readily available. Typically, high-resolution imagery can be obtained, depending on the size of the input object, the illumination wavelength, and the f-number of the lenses. Basic and more general configurations are presented, along with experimental results clearly showing image shearing, rotation, and a combination of these with high-quality output imagery.  相似文献   
57.
A polyanhydride implant containing gentamicin sulfate was fabricated using a laboratory-scale injection-molding machine. After injection molding, the implants were subject to heat treatment at 60°C for various time periods with or without nitrogen protection. The impact of this heat treatment on the in vitro properties of the implants including copolymer molecular weights, mechanical properties, and in vitro drug-release profiles was investigated. This heat treatment caused a drastic drop in the molecular weight of the copolymer. Heating without nitrogen protection resulted in the hardening of the implant, but heating in the presence of nitrogen rendered the implant less rigid. It was also found that a faster in vitro drug release profile was shown by implants heated without nitrogen protection and a pronounced slowing down in drug release was exhibited by implants heated with nitrogen protection.  相似文献   
58.
Most studies of coronavirus disease 2019(COVID-19) progression have focused on the transfer of patients within secondary or tertiary care hospitals from regular wards to intensive care units. Little is known about the risk factors predicting the progression to severe COVID-19 among patients in community isolation, who are either asymptomatic or suffer from only mild to moderate symptoms. Using a multivariable competing risk survival analysis, we identify several important predictors of progressi...  相似文献   
59.
Mold fluxes are synthetic slags used to coverthe liquid steel meniscus during continuous castingof steel.The flux,whichis continuously fed on thesurface of liquid pool during casting,melts first andthenflowsintothe gap between mold wall and solid-ified steel shell.It is well known that the perform-ance of the flux can greatly affect both the castingoperation and product quality.Because of its i mpor-tance,intensiveinvestigations have been performed,and considerable progress has been made[1-6].…  相似文献   
60.
Due to the complexity of modern industrial systems, a conventional automation system is not capable of providing sufficient information management and high-level intelligent approaches, as achieving these functionalities requires the support of comprehensive data management and coordination between system devices and heterogenous information. This paper proposes the concept of e-Automation, in which computer networking and distributed intelligence agent technologies are applied to industrial automation systems, and presents a hardware and software architecture that implements this concept. An open infrastructure based on multi-agent systems is employed in the proposed architecture of e-Automation, which aims to allow the implementation of diverse tasks and to permit greater configurability than can be obtained from a traditional system. To evaluate our proposed e-Automation concept, this paper presents a case study of substation information management which adopts the proposed e-Automation architecture in power system domain.  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