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   559篇
  免费   49篇
  国内免费   1篇
电工技术   7篇
综合类   1篇
化学工业   121篇
金属工艺   7篇
机械仪表   9篇
建筑科学   18篇
能源动力   20篇
轻工业   90篇
水利工程   6篇
石油天然气   2篇
无线电   54篇
一般工业技术   79篇
冶金工业   48篇
原子能技术   3篇
自动化技术   144篇
  2023年   8篇
  2022年   24篇
  2021年   37篇
  2020年   27篇
  2019年   24篇
  2018年   31篇
  2017年   24篇
  2016年   22篇
  2015年   17篇
  2014年   39篇
  2013年   47篇
  2012年   39篇
  2011年   42篇
  2010年   35篇
  2009年   31篇
  2008年   21篇
  2007年   14篇
  2006年   15篇
  2005年   11篇
  2004年   13篇
  2003年   8篇
  2002年   6篇
  2001年   3篇
  2000年   5篇
  1999年   2篇
  1998年   19篇
  1997年   7篇
  1996年   9篇
  1995年   3篇
  1994年   7篇
  1993年   2篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1980年   1篇
  1977年   3篇
  1976年   1篇
  1975年   1篇
排序方式: 共有609条查询结果,搜索用时 15 毫秒
51.
In this paper, we approach the removal of back-to-front interferences from scans of double-sided documents as a blind source separation problem, and extend our previous linear mixing model to a more effective nonlinear mixing model. We consider the front and back ideal images as two individual patterns overlapped in the observed recto and verso scans, and apply an unsupervised constrained maximum likelihood technique to separate them. Through several real examples, we show that the results obtained by this approach are much better than the ones obtained through data decorrelation or independent component analysis. As compared to approaches based on segmentation/classification, which often aim at cleaning a foreground text by removing all the textured background, one of the advantages of our method is that cleaning does not alter genuine features of the document, such as color or other structures it may contain. This is particularly interesting when the document has a historical importance, since its readability can be improved while maintaining the original appearance.  相似文献   
52.
In this paper, we address the resource constrained project scheduling problem with uncertain activity durations. Project activities are assumed to have known deterministic renewable resource requirements and uncertain durations, described by independent random variables with a known probability distribution function. To tackle the problem solution we propose a heuristic method which relies on a stage wise decomposition of the problem and on the use of joint probabilistic constraints.  相似文献   
53.
This paper focuses on the scheduling and congestion control problems for a band limited communication network, taking into account the QoS requirements of the various connections. The problem is tackled and solved using optimal control methodologies. The optimal solution is given a closed form representation and is characterized by the classical closed loop structure. Applications against simulated realistic data show the improvements achievable by the proposed approach.  相似文献   
54.
With reference to a (discrete time) linear system filtering problem, we consider the problem of online deciding at which instant we actually measure and process the output values. We propose a convenient measurement policy, able to sensibly reduce the measurement cost, while keeping the estimate accuracy at satisfactory levels. By some probabilistic arguments we analyse the upper bounds for the measurement and non-measurement time intervals.  相似文献   
55.
A polyphasic approach, involving both genotypic and phenotypic analyses was used to characterize 33 isolates of lactic acid bacteria from the raw milk Protected Designation of Origin (PDO) Canestrato Pugliese cheese, in order to select candidate strains that can be used as autochthonous starter cultures in the dairy industry. Randomly amplified polymorphic DNA (RAPD) analysis and clustering by the unweighted pair-group method with arithmetic averages (UPGMA) were used to evaluate the genotypic diversity, while phenotypic characterization was performed through miniaturized assays and traditional biochemical tests. Technological properties of major interest for cheese-making (acidification, tendency to lysis, proteolytic and peptidase activity) were also evaluated, and selected subset of data was statistically examined by the one-way ANOVA and the Tukey-Kramer HSD test, to highlight strain-specific and species-specific differences among the isolates. A high degree of diversity appeared in the phenotypic and technological traits in opposition to a relatively low genotypic diversity. Although none of the isolates showed the best performances in all the activities, an appropriate mixture of strains could be selected for providing an efficacious autochthonous starter culture.  相似文献   
56.
The paper presents a consideration of public sector operations as an alternative to the privatization of water and sewerage services. Cross-country case studies of publicly owned enterprises which have succeeded in reconciling efficiency and social purposes and carrying out structural and managerial changes are compared with some experiences of privatized concessions. Overall, public enterprises appear no less efficient that private companies, while being capable of development-oriented consideration of public interests.  相似文献   
57.
A stepwise surface functionalization procedure, based on hybrid covalent and non-covalent approach is herein proposed to anchor tetra-anionic meso-tetrakis(4-sulfonatophenyl)porphyrin on ZnO nanorods. Carboxyalkylphosphonic acids have been proven effective to form stable self-assembled monolayers through the surface grafting of –PO3H2 headgroups. The exposed carboxylic functionalities are suitable for the successful grafting of cationic poly-l-lysine that drives, in water, the non-covalent anchoring of the anionic porphyrin. A stepwise surface characterization, provided by X-ray photoelectron spectroscopy, elucidates the multilayers deposition and surface composition after each process step, thus, giving interesting insights on the chemical speciation of the exposed functionalities. UV–vis spectroscopy confirms the role of ZnO morphology to increase the porphyrin loading onto the investigated surfaces. The proposed approach is effective to achieve deposition of anionic porphyrins on ZnO nanostructures and combines the robustness of covalent functionalization with the versatility and full reversibility of the non-covalent strategies.  相似文献   
58.
Chronic inflammation is widely diffuse in maintenance hemodialysis (MHD) patients and is associated with poor survival. Hemodiafiltration with endogenous reinfusion (HFR) is a dialysis technique, highly biocompatible, able to adsorb proinflammatory cytokines and to decrease amino acids and antioxidants loss. These features could be helpful in MHD patients affected by idiopathic chronic inflammation, but this issue remains to be elucidated. We performed a multicenter longitudinal study to assess the effect of the switching from bicarbonate HD to HFR in patients with serum C‐reactive Protein (CRP) > 5 mg/L coupled with albumin <4.0 g/dL in the last 6 months. We enrolled 24/176 (14%) patients, of which 20 patients were assessed at 4 months and 18 completed the study. We excluded 11 patients with evident causes of inflammation. At baseline, serum levels of CRP (18.7[7.0–39.4] mg/L) and albumin (3.5[3.3–3.7] g/dL) were significantly correlated (r = ?0.49; P = 0.028). The effect on CRP and albumin was almost evident in the first 4 months and remained stable until to eighth month. A strict correlation (R = ?0.49; 0.040) between percentage change of CRP (?35%) and albumin (+14%) after 8 months of HFR. These effects were associated with the reduction of IL‐6, IL‐1β, and TNF‐α and the increment of pre‐albumin and leptin, whereas the serum levels of Branched Chain Amino Acid (BCAA) remained unchanged. In MHD patients affected by idiopathic chronic inflammation the switching from BHD to HFR is associated with improvement of inflammation. Whether these favorable effects may modify the outcomes of these high‐risk patients needs to be confirmed by studies ad hoc.  相似文献   
59.
60.
A comparative study of the self‐assembly at a variety of surfaces of a dithiophene rotaxane 1 ?β‐CD and its corresponding dumbbell, 1, by means of atomic force microscopy (AFM) imaging and scanning tunneling microscopy (STM) imaging on the micrometer and nanometer scale, respectively. The dumbbell is found to have a greater propensity to form ordered supramolecular assemblies, as a result of π–π interactions between dithiophenes belonging to adjacent molecules, which are hindered in the rotaxane. The fine molecular structure determined by STM was compared to that obtained by molecular modelling. The optical properties of both rotaxane and dumbbell in the solid state were investigated by steady‐state and time‐resolved photoluminescence (PL) experiments on spin‐cast films and diluted solutions. The comparison between the optical features of the threaded and unthreaded systems reveals an effective role of encapsulation in reducing aggregation and exciton migration for the rotaxanes with respect to the dumbbells, thus leading to higher PL quantum efficiency and preserved single‐molecule photophysics for longer times after excitation in the threaded oligomers.  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