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   150498篇
  免费   6709篇
  国内免费   3357篇
电工技术   4647篇
技术理论   10篇
综合类   6750篇
化学工业   22674篇
金属工艺   8266篇
机械仪表   6834篇
建筑科学   7496篇
矿业工程   2372篇
能源动力   2988篇
轻工业   8814篇
水利工程   2541篇
石油天然气   3985篇
武器工业   526篇
无线电   17273篇
一般工业技术   24435篇
冶金工业   5995篇
原子能技术   965篇
自动化技术   33993篇
  2024年   310篇
  2023年   1175篇
  2022年   2086篇
  2021年   2863篇
  2020年   2244篇
  2019年   1784篇
  2018年   16171篇
  2017年   15256篇
  2016年   11840篇
  2015年   3259篇
  2014年   3554篇
  2013年   4068篇
  2012年   7372篇
  2011年   13926篇
  2010年   12012篇
  2009年   9132篇
  2008年   10329篇
  2007年   11096篇
  2006年   3381篇
  2005年   4046篇
  2004年   3242篇
  2003年   3036篇
  2002年   2252篇
  2001年   1638篇
  2000年   1861篇
  1999年   2058篇
  1998年   1756篇
  1997年   1421篇
  1996年   1421篇
  1995年   1151篇
  1994年   1015篇
  1993年   703篇
  1992年   554篇
  1991年   415篇
  1990年   338篇
  1989年   308篇
  1988年   228篇
  1987年   154篇
  1986年   110篇
  1985年   82篇
  1984年   61篇
  1983年   41篇
  1982年   52篇
  1968年   45篇
  1966年   44篇
  1965年   48篇
  1958年   38篇
  1957年   36篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The business value of information technology (IT) has been one of the top concerns of both practitioners and scholars for decades. Numerous studies have documented the positive effects of IT capability on organizational performance but our knowledge of the processes through which such gains are achieved remains limited due to a lack of focus on the business environment. Such a linkage therefore remains the subject of debate in the information systems literature. In this study, we fill this gap by investigating the mediating role of business process agility and the moderating roles of environmental factors. On the basis of matched survey data obtained from 214 IT and business executives from manufacturing firms in China, our analyses show that even though firm-wide IT capability presents the characteristics of rarity, appropriability, non-reproducibility, and non-substitutability, its impact on organizational performance is fully mediated by business process agility. Our results also show that the impact of the environment is multifaceted and nuanced. In particular, environmental hostility weakens the effect of IT capability on business process agility, while environmental complexity strengthens it. The theoretical and practical implications of this study, and its limitations, are also discussed.  相似文献   
992.
Clinical pathway is an approach to standardise care processes to support the implementations of clinical guidelines and protocols. It is designed to support the management of treatment processes including clinical and non-clinical activities, resources and also financial aspects. It provides detailed guidance for each stage in the management of a patient with the aim of improving the continuity and coordination of care across different disciplines and sectors. However, in the practical treatment process, the lack of knowledge sharing and information accuracy of paper-based clinical pathways burden health-care staff with a large amount of paper work. This will often result in medical errors, inefficient treatment process and thus poor quality medical services. This paper first presents a theoretical underpinning and a co-design research methodology for integrated pathway management by drawing input from organisational semiotics. An approach to integrated clinical pathway management is then proposed, which aims to embed pathway knowledge into treatment processes and existing hospital information systems. The capability of this approach has been demonstrated through the case study in one of the largest hospitals in China. The outcome reveals that medical quality can be improved significantly by the classified clinical pathway knowledge and seamless integration with hospital information systems.  相似文献   
993.
孙路  兰巨龙 《计算机工程》2014,(6):45-48,52
现有队列调度算法只能满足某一种特定类型业务流量的服务质量(QoS)需求,无法广泛支持多种类型业务流量。为此,提出一种基于区分服务的嵌套队列调度算法。将现有队列调度算法通过嵌套模型进行组合,并根据该嵌套模型进行队列调度,从而为多种类型业务流量提供均衡的QoS保障。仿真结果表明,该算法能够满足不同类型业务流量的QoS需求,其各项性能指标所达效果与最优效果的差距较小,并且在多种类型业务流量的支持方面比现有队列调度算法表现更好。  相似文献   
994.
端点检测是语音信号处理的一个关键环节。为提高语音在低性噪比以及非平稳噪声环境下的端点检测性能,在长时信号变化特征(LTSV)的基础上提出一种新的D-LTSV语音端点检测方法。采用Bartlett-Welch方法估计语音谱,分析语音谱在长时域上的熵,利用倒谱的动态特性分析方法提取连续帧熵值的动态变化特征。实验结果表明,D-LTSV综合考虑了语音的非平稳性和帧间非平稳性的动态变化情况,具有比LTSV更好的分辨能力,特别是在低性噪比和非平稳噪声的环境下,D-LTSV的分辨能力提升了50.77%,能够准确地进行端点检测,具有更强的鲁棒性。  相似文献   
995.
目前,自然语言处理已从句法、词法层面走向轻量级语义层面。针对中文陈述句的自然语言处理,传统Lambek演算无法解决中文陈述句灵活语序的问题,而现有的方法加入模态词、新连接词等后,又进一步增加了已经是NP-hard的Lambek演算的复杂性,因此并不适合计算机的相关处理。基于此,采用加标动词匹配的Lambek演算对中文陈述句灵活语序进行处理。加标动词匹配算法的时间复杂度低,使得计算机及其程序能有效地对中文陈述句灵活语序进行处理,并能通过Curry-Howard对应理论与λ-演算引入轻量级语义处理。  相似文献   
996.
碳,氮对氧化锆相结构稳定性的作用   总被引:3,自引:0,他引:3  
顾守仁  马楷 《硅酸盐学报》1995,23(5):507-513
利用热处理研究了碳、氮对氧化锆相结构和相变的影响。实验结果表明:碳、氢原子在高温下可以渗入到氧化锆中去,阻止了氧化锆高温相(四方相和立方相)在冷却过程中向低温相(单斜相)的转变。  相似文献   
997.
The removal of hydrogen sulfide (H2S) from simulated gas was carried out in a batch type fluidized-bed reactor using natural manganese ore (NMO), which consists of several metal oxides (MnOx: 51.85%, FeOy: 3.86%, CaO: 0.11%). The H2S breakthrough curves were obtained by changing temperature, gas velocity, initial H2S concentration, and aspect ratio. Moreover, the effects of the particle size and the particle-mixing fraction on H2S removal were investigated in a binary system of different particle size. From this study, H2S removal efficiency increased with increasing temperature but decreased with increasing excess gas velocity. The breakthrough time for H2S decreased as the gas velocity increased, which leads to reducing gas-solid contacting due to gas bypassing in a fluidized bed reactor. Improvement of H2S removal efficiency in continuous process can be expected from the results of the binary particle system with different size in a batch experiment. The NMO could be considered as a potential sorbent in H2S removal.  相似文献   
998.
微铬含量CO中温变换催化剂本征动力学的研究崔波,赵素芳,刘鹏照,宋世英,张洪全(青岛化工学院化学工程系,青岛266042)关键词:催化剂,一氧化碳变换反应,铁催化剂,动力学1前言一氧化碳变换反应是化学工业中制氢的重要反应,长期以来所用的一氧比碳中变催...  相似文献   
999.
Novel silica nanoboxes were prepared by controlled dealumination of Na-X and Ca-A type zeolites using ammonium hexafluorosilicate (AHFS). The silica-richer the parent zeolite, the smaller the average pore size produced and the narrower the pore size distribution obtained. This was due to the specific reactivity of the extracting agent with the zeolite framework aluminum atoms. High temperature calcination of the dealuminated X-zeolite (ammonium form) resulted in mesoporous materials exhibiting an ink-bottle shape, a quite high surface area (330 m2/g, no micropores), an average pore diameter of 4.5 nm with a quite narrow pore size distribution (± 1.0 nm) and finally, a pore opening diameter of 3.9 nm. The latter was determined by using the nitrogen sorption isotherms (BET technique) and related pore volume data. The sorption behavior also suggested the interconnecting character of the newly created nanoboxes. The periodicity of these nanoboxes throughout the mesoporous material was clearly shown by X-ray powder diffraction at very small angles. These materials, herein called monomodal nanoboxes because of the absence of micropores in the structure, were also thermally stable. Incorporation of orthosilicate into the obtained silica nanoboxes, in accordance with the recently developed technique for pore size engineering in zeolites, led to materials with smaller pore openings but having almost the same textural properties. Solid superacidic materials were prepared by incorporating a liquid superacid (triflic acid or trifluoromethanesulfonic acid) into the silica nanoboxes using the wet impregnation technique. The maximum triflic acid loading which did not significantly affect the mesoporous framework of the materials was 24 wt%. As a reference, the maximum loading of less acidic sulfuric acid was slightly lower. All this showed the high chemical stability of the silica nanoboxes for supporting very acidic species. Temperature-programmed desorption using a combined DTA/TGA system allowed the identification of the bound phases and some liquid phase of the loaded triflic acid.  相似文献   
1000.
曹春蕾  鹿育萨 《化工之友》2007,26(19):58-60
目的探讨高胆固醇兔脑组织RAAS与氧化应激的关系及培哚普利、缬沙坦的干预效果;方法:32只健康新西兰白兔随机分为4组:正常组,高脂组,培哚普利组,缬沙坦组。喂饲8周后,测定血清总胆固醇(Total cholesterol,TC)及低密度脂蛋白(Low den-sity lipoprotein,LDL)浓度。取脑组织测血管紧张素Ⅱ(AngiotensinⅡ,AngⅡ),血红素氧合酶(hemo oxygenase-1,HO-1)的表达及超氧化物岐化酶(SOD)活力,丙二醛(MDA)含量;结果:与正常组相比,高脂组AngⅡ,HO-1表达明显增强,SOD活力下降,MDA升高,培哚普利可降低AngⅡ,而缬沙坦不能,二者均可使HO-1表达上调,SOD活力升高,MDA降低;结论:1)高胆固醇血症时脑组织处于氧化应激状态,肾素血管紧张素醛固酮系统(Rennin-angiotensin-aldosterone system RAAS)激活;2)培哚普利和缬沙坦对组织具有抗氧化应激的保护作用。  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