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   756篇
  免费   56篇
电工技术   11篇
化学工业   146篇
金属工艺   2篇
机械仪表   7篇
建筑科学   28篇
矿业工程   1篇
能源动力   3篇
轻工业   108篇
水利工程   1篇
石油天然气   1篇
无线电   67篇
一般工业技术   138篇
冶金工业   51篇
原子能技术   1篇
自动化技术   247篇
  2024年   2篇
  2023年   6篇
  2022年   12篇
  2021年   25篇
  2020年   10篇
  2019年   24篇
  2018年   20篇
  2017年   26篇
  2016年   31篇
  2015年   27篇
  2014年   41篇
  2013年   63篇
  2012年   57篇
  2011年   66篇
  2010年   52篇
  2009年   62篇
  2008年   47篇
  2007年   42篇
  2006年   33篇
  2005年   23篇
  2004年   32篇
  2003年   26篇
  2002年   18篇
  2001年   11篇
  2000年   6篇
  1999年   3篇
  1998年   10篇
  1997年   6篇
  1996年   6篇
  1995年   5篇
  1994年   6篇
  1993年   5篇
  1992年   1篇
  1990年   2篇
  1989年   2篇
  1986年   1篇
  1984年   1篇
  1980年   1篇
  1974年   1篇
排序方式: 共有812条查询结果,搜索用时 31 毫秒
101.
A new design of a BIC sensor for current testing static CMOS circuits is proposed. It is based on a lateral BJT device which is easy to incorporate in any standard CMOS process. The design diverts a fraction of the I DDQ current from the cell under test and a resistive component generates a voltage proportional to I DDQ . Additional features are the possibility of continuous measure of i dd and increased speed of this sensor compared with sensors based on the current integration principle. The design does not have substrate currents due to the parasitic vertical BJTs. Experimental work on the sensor is reported.  相似文献   
102.
Our objective was to examine social class and educational differences in long-term smoking cessation success among a cohort of smokers attending a specialized smoking clinic. We studied sustained abstinence after cessation among 1,516 smokers (895 men and 621 women) treated for smoking cessation between 1995 and 2001 at a university teaching hospital in the metropolitan area of Barcelona, Spain. We calculated 1-year and long-term (up to 8-year) abstinence probabilities by means of Kaplan-Meier curves and the hazard ratio of relapse by means of Cox regression, after adjusting for other predictors of relapse. Overall abstinence probability was .277 (95% CI = .254-.301). Men and women in social classes IV-V had significant hazard ratios of relapse after long-term follow-up (men: 1.36, 95% CI = 1.07-1.72; women: 1.60, 95% CI = 1.24-2.06), as compared with patients in social classes I-II. The same independent effect was observed for education: Men and women with primary or less than primary studies had higher hazard ratios of relapse (men: 1.75, 95% CI = 1.35-2.25; women: 1.92, 95% CI = 1.51-2.46), as compared with patients with a university degree. Similar estimates were obtained after adjustment for stage of change, Fagerstr?m score for nicotine dependence, and type of treatment. Patients of lower socioeconomic status are at higher risk of relapse, and this association is independent of other well-known predictors of relapse. Social differences have to be taken into account in the clinical setting when tailoring specific actions to treat smoking dependence.  相似文献   
103.
A new scheme to alleviate contention in optical burst switching networks is proposed. It consists of preventively reserving resources in a node, to be used if resources are busy on the next hop node. The burst is sent back to the preceding node and then resent forward. Simulations are carried out to assess the feasibility of the proposed scheme. Its performance is compared with that of contention resolution based on deflection routing.  相似文献   
104.
This paper investigates selective sharing of load current components among the parallel operation of distributed generators (DGs) in three-phase four-wire stand-alone microgrids. The proposed control method is based on master-slave operation of DGs, and the goal of selective sharing of load current components is to have DGs located in close proximity of the load operating in slave mode, in order to inject their available energy and also compensate the non-active load current components, while the distant DGs might operate in master mode to share the remaining load autonomously. Droop control is employed due to impracticality of communication at remote nodes, and resistive line impedance compensation is adopted to decouple active and reactive power controllers and ensure proper active power sharing among master DGs, irrespective of the mitigation of non-active current components by the slave inverters. The sharing factors for each current component are determined by a higher level control. The Conservative Power Theory (CPT) decompositions provide decoupled power and current references for the inverters, resulting in a selective sharing strategy. The principles supporting the developed control strategy are discussed, and the effectiveness of the control is demonstrated through computational simulations using PSIM software.  相似文献   
105.
Lipid accumulation in the human liver seems to be a crucial mechanism in the pathogenesis and the progression of non-alcoholic fatty liver disease (NAFLD). We aimed to evaluate gene expression of different fatty acid (FA) metabolism-related genes in morbidly obese (MO) women with NAFLD. Liver expression of key genes related to de novo FA synthesis (LXRα, SREBP1c, ACC1, FAS), FA uptake and transport (PPARγ, CD36, FABP4), FA oxidation (PPARα), and inflammation (IL6, TNFα, CRP, PPARδ) were assessed by RT-qPCR in 127 MO women with normal liver histology (NL, n = 13), simple steatosis (SS, n = 47) and non-alcoholic steatohepatitis (NASH, n = 67). Liver FAS mRNA expression was significantly higher in MO NAFLD women with both SS and NASH compared to those with NL (p = 0.003, p = 0.010, respectively). Hepatic IL6 and TNFα mRNA expression was higher in NASH than in SS subjects (p = 0.033, p = 0.050, respectively). Interestingly, LXRα, ACC1 and FAS expression had an inverse relation with the grade of steatosis. These results were confirmed by western blot analysis. In conclusion, our results indicate that lipogenesis seems to be downregulated in advanced stages of SS, suggesting that, in this type of extreme obesity, the deregulation of the lipogenic pathway might be associated with the severity of steatosis.  相似文献   
106.
A method to optimize triangular and quadrilateral meshes on parameterized surfaces is proposed. The optimization procedure relocates the nodes on the surface to improve the quality (smooth) and ensures that the elements are not inverted (untangle). We detail how to express any measure for planar elements in terms of the parametric coordinates of the nodes. The extended measures can be used to check the quality and validity of a surface mesh. Then, we detail how to optimize any Jacobian-based distortion measure to obtain smoothed and untangled meshes with the nodes on the surface. We prove that this method is independent of the surface parameterization. Thus, it can optimize meshes on CAD surfaces defined by low-quality parameterizations. The examples show that the method can optimize meshes composed by a large number of inverted elements. Finally, the method can be extended to obtain high-order meshes with the nodes on the CAD surfaces.  相似文献   
107.
Hydroxyapatite foams are potential synthetic bone grafting materials or scaffolds for bone tissue engineering. A novel method to obtain injectable hydroxyapatite foams consists in foaming the liquid phase of a calcium phosphate cement. In this process, the cement powder is incorporated into a liquid foam, which acts as a template for macroporosity. After setting, the cement hardens maintaining the macroporous structure of the foam. In this study a low molecular weight surfactant, Polysorbate 80, and a protein, gelatine, were compared as foaming agents of a calcium phosphate cement. The foamability of Polysorbate 80 was greater than that of gelatine, resulting in higher macroporosity in the set hydroxyapatite foam and higher macropore interconnectivity. Gelatine produced less interconnected foams, especially at high concentrations, due to a higher liquid foam stability. However it increased the injectability and cohesion of the foamed paste, and enhanced osteoblastic-like cell adhesion, all of them important properties for bone grafting materials.  相似文献   
108.
In this study, we present a method designed to generate dynamic holograms in holographic optical tweezers. The approach combines our random mask encoding method with iterative high-efficiency algorithms. This hybrid method can be used to dynamically modify precalculated holograms, giving them new functionalities-temporarily or permanently-with a low computational cost. This allows the easy addition or removal of a single trap or the independent control of groups of traps for manipulating a variety of rigid structures in real time.  相似文献   
109.
110.
The index introduced here provides a normalized measure of the effectiveness of any semicoherent structure. We study the mathematical properties of the index and derive different axiomatic characterizations for it. Moreover, close relationships are shown to reliability functions and also to the Birnbaum structural importance measure—for which twice the performance index plays the role of potential function—that give rise to computational procedures. Some numerical examples illustrate the application of the index.  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