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   29163篇
  免费   2651篇
  国内免费   853篇
电工技术   909篇
技术理论   1篇
综合类   890篇
化学工业   7568篇
金属工艺   1146篇
机械仪表   1171篇
建筑科学   1520篇
矿业工程   312篇
能源动力   817篇
轻工业   4800篇
水利工程   448篇
石油天然气   626篇
武器工业   106篇
无线电   2181篇
一般工业技术   3911篇
冶金工业   2448篇
原子能技术   204篇
自动化技术   3609篇
  2024年   141篇
  2023年   495篇
  2022年   1616篇
  2021年   1914篇
  2020年   1046篇
  2019年   914篇
  2018年   1007篇
  2017年   1134篇
  2016年   1106篇
  2015年   1148篇
  2014年   1494篇
  2013年   1905篇
  2012年   1969篇
  2011年   2161篇
  2010年   1717篇
  2009年   1642篇
  2008年   1501篇
  2007年   1394篇
  2006年   1184篇
  2005年   931篇
  2004年   703篇
  2003年   603篇
  2002年   576篇
  2001年   449篇
  2000年   341篇
  1999年   376篇
  1998年   614篇
  1997年   496篇
  1996年   361篇
  1995年   244篇
  1994年   197篇
  1993年   185篇
  1992年   124篇
  1991年   85篇
  1990年   92篇
  1989年   73篇
  1988年   64篇
  1987年   64篇
  1986年   66篇
  1985年   64篇
  1984年   51篇
  1983年   41篇
  1982年   34篇
  1981年   57篇
  1980年   42篇
  1979年   35篇
  1978年   34篇
  1977年   42篇
  1976年   41篇
  1975年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
目前,对管线钢焊缝应力腐蚀行为研究较多,而针对其点蚀行为的研究很少。采用动电位极化和电化学阻抗谱研究了X80钢母材和焊缝在高pH值土壤模拟溶液(0.50 mol/LNaHCO_3+0.02 mol/LNaCl)中的点蚀行为,通过金相显微镜观察了母材和焊缝的显微组织和极化后的点蚀形貌,借助Mott-Schokkty曲线分析了钝化膜的半导体特性。结果表明:X80钢母材和焊缝在高pH值土壤模拟溶液中都能够发生钝化,但母材的钝化区间范围更宽,击穿电位更高。母材和焊缝表面所成的钝化膜都呈n型半导体特征,但母材表面的钝化膜致密性和均匀性更好,膜电阻和电荷转移电阻更大,钝化膜内的缺陷密度也更低,这是导致母材抗点蚀性能优于焊缝的一个原因。此外,焊缝组织中高含量的贝氏体组织是造成其点蚀性能下降的另一个因素。  相似文献   
992.
The objectives of this study were to evaluate the characteristics of commercial soft drinks related with the corrosion process of the aluminium packaging and based on that, propose model solutions for future studies of beverage/package interaction and corrosion process of metal packages. Therefore, the pH, acidity, concentration of chlorides and copper in six types of soft drinks were determined, as well as the corrosion potential of the aluminium and the current density corrosion obtained in polarization curves using the beverages as electrolyte. Based on the results obtained, a solution of citric acid (pH = 3) containing chloride (250 mg/kg) and copper ions (250 µg/kg) is proposed. The obtained results are potentially useful for the industry and future studies regarding the interaction process between soft drinks and aluminium cans. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
993.
谭浩  徐迪 《包装工程》2018,39(22):12-16
目的 探讨设计师在情境作用下的系统性思维过程,旨在构建基于情境的产品交互设计思维模型,为设计师如何设计出用户体验较好的产品提供思路。方法 以设计思维作为研究对象,将设计过程置于情境分析中,采用理论框架构建和实验验证的方法,基于“5W1H”方法构建情境组织模型,以分析设计过程中的情境作用。结论 通过实验及分析进一步提出基于情境作用的产品交互设计思维模型,在设计过程具有一定的参考作用,有利于促进设计师开展产品交互设计活动,完善其设计方案,以提升产品的体验感。  相似文献   
994.
本文对Al2O3基陶瓷复合材料Al2O3-ZrO2-SiCw进行了干摩擦磨损试验,并运用了SEM,TEM和XRD等手段对其显微结构、力学性能及它们与GCr15钢对摩时的摩擦磨损行为进行了系统分析,在此基础上深入探讨了SiC晶须(SiCw)增韧补强作用对复合材料的摩擦磨损性能的影响。  相似文献   
995.
董迪 《包装工程》2022,43(15):234-240
目的 设计质量、强度满足使用的可循环拉链邮袋,代替一次性邮袋,实现绿色发展理念。方法 设计可循环拉链邮袋结构,基于有限元分析模拟拉链邮袋实际应用中真实物理系统。分析拉链邮袋在材质、夹具固定方式、负载3种影响因素下的应力、应变、变形情况,比较仿真结果,确定可循环拉链邮袋材质并验证。结果 不同材质下,涤纶树脂(PET)变形量较小,高密度聚乙烯(HDPE)次之,聚丙烯(PP)变形量较大。不同固定方式下,袋口两短边夹具固定,袋口应力较集中,最大位移和应变较大,袋口四边夹具固定袋口变形较小、应力较小。不同负载下,负载与应力、位移、应变三者变化呈正相关,最大应力、位移、应变出现的位置较为稳定。结论 借助有限元分析模拟拉链邮袋实际应用中受力情况,分析不同材质、夹具固定方式、负载情况下,可循环拉链邮袋力学性能,节省人力、物力,为实际应用提供依据,同时,证明了涤纶树脂(PET)可应用于可循环拉链邮袋的制作,为绿色、环保、可降解、可循环拉链邮袋的制作奠定基础,对限塑、绿色发展有着重要的意义。  相似文献   
996.
The future of lithium metal batteries as a widespread, safe and reliable form of high-energy-density rechargeable battery depends on a significant advancement in the electrolyte material used in these devices. Molecular solvent-based electrolytes have been superceded by polymer electrolytes in some prototype devices, primarily in a drive to overcome leakage and flammability problems, but these often exhibit low ionic conductivity and prohibitively poor lithium-ion transport. To overcome this, it is necessary to encourage dissociation of the lithium ion from the anionic polymer backbone, ideally without the introduction of competing, mobile ionic species. Here we demonstrate the effect of zwitterionic compounds, where the cationic and anionic charges are immobilized on the same molecule, as extremely effective lithium ion 'dissociation enhancers'. The zwitterion produces electrolyte materials with conductivities up to seven times larger than the pure polyelectrolyte gels, a phenomenon that appears to be common to a number of different copolymer and solvent systems.  相似文献   
997.
A complete set up of optimal process conditions for an effective colloidal lithography/catalyst assisted MOCVD process integration is presented. It mainly focuses on the determination of the deposition temperature threshold for ZnO Metal-Organic Chemical Vapour Deposition (MOCVD) as well as the concentration of metal-organic silver (Ag) catalyst. Indeed, the optimization of such process parameters allows to tailor the ZnO film morphology in order to make the colloidal lithography/catalyst assisted MOCVD approach a valuable bottom up method to fabricate bi-dimensional ordered ZnO nanohole arrays.  相似文献   
998.
Resistive switching memories are nonvolatile memory cells based on nano‐ionic redox processes and offer prospects for high scalability, ultrafast write and read access, and low power consumption. In two‐terminal cation based devices a nanoscale filament is formed in a switching material by metal ion migration from the anode to the cathode. However, the filament growth and dissolution mechanisms and the dynamics involved are still open questions, restricting device optimization. Here, a spectroscopic technique to optically characterize in situ the resistive switching effect is presented. Resistive switches arranged in a nanoparticle‐on‐mirror geometry are developed, exploiting the high sensitivity to morphological changes occurring in the tightly confined plasmonic hotspot within the switching material. The focus is on electrochemical metallization and the optical signatures detected over many cycles indicate incomplete removal of metal particles from the filament upon RESET and suggest that the filament can nucleate from different positions from cycle to cycle. The technique here is nondestructive and the measurements can be easily performed in tunable ambient conditions and with realistic cell geometries.  相似文献   
999.
Future climate scenarios suggest that crop plants will experience environmental changes capable of affecting their productivity. Among the most harmful environmental stresses is drought, defined as a total or partial lack of water availability. It is essential to study and understand both the damage caused by drought on crop plants and the mechanisms implemented to tolerate the stress. In this study, we focused on four cultivars of tomato, an economically important crop in the Mediterranean basin. We investigated the biochemical mechanisms of plant defense against drought by focusing on proteins specifically involved in this stress, such as osmotin, dehydrin, and aquaporin, and on proteins involved in the general stress response, such as HSP70 and cyclophilins. Since sugars are also known to act as osmoprotectants in plant cells, proteins involved in sugar metabolism (such as RuBisCO and sucrose synthase) were also analyzed. The results show crucial differences in biochemical behavior among the selected cultivars and highlight that the most tolerant tomato cultivars adopt quite specific biochemical strategies such as different accumulations of aquaporins and osmotins. The data set also suggests that RuBisCO isoforms and aquaporins can be used as markers of tolerance/susceptibility to drought stress and be used to select tomato cultivars within breeding programs.  相似文献   
1000.
Ectopic endometrial epithelium associates a wide spectrum of symptomatology. Their evolution can be influenced by inflammatory and vascular changes, that affect not only the structure and cell proliferation rate, but also symptoms. This prospective study involved tissue samples from surgically treated patients, stained using classical histotechniques and immunohistochemistry. We assessed ectopic endometrial glands (CK7+, CK20−), adjacent blood vessels (CD34+), estrogen/progesterone hormone receptors (ER+, PR+), inflammatory cells (CD3+, CD20+, CD68+, Tryptase+), rate of inflammatory cells (Ki67+) and oncoproteins (BCL2+, PTEN+, p53+) involved in the development of endometriosis/adenomyosis. A CK7+/CK20− expression profile was present in the ectopic epithelium and differentiated it from digestive metastases. ER+/PR+ were present in all cases analyzed. We found an increased vascularity (CD34+) in the areas with abdominal endometriosis and CD3+−:T-lymphocytes, CD20+−:B-lymphocytes, CD68+:macrophages, and Tryptase+: mastocytes were abundant, especially in cases with adenomyosis as a marker of proinflammatory microenvironment. In addition, we found a significantly higher division index-(Ki67+) in the areas with adenomyosis, and inactivation of tumor suppressor genes-p53+ in areas with neoplastic changes. The inflammatory/vascular/hormonal mechanisms trigger endometriosis progression and neoplastic changes increasing local pain. Furthermore, they may represent future therapeutic targets. Simultaneous-multiple immunohistochemical labelling represents a valuable technique for rapidly detecting cellular features that facilitate comparative analysis of the studied predictors.  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