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   749篇
  免费   23篇
  国内免费   1篇
电工技术   6篇
化学工业   136篇
金属工艺   16篇
机械仪表   11篇
建筑科学   35篇
矿业工程   1篇
能源动力   18篇
轻工业   59篇
水利工程   2篇
石油天然气   1篇
无线电   75篇
一般工业技术   145篇
冶金工业   154篇
原子能技术   4篇
自动化技术   110篇
  2024年   2篇
  2023年   4篇
  2022年   18篇
  2021年   17篇
  2020年   16篇
  2019年   11篇
  2018年   14篇
  2017年   13篇
  2016年   10篇
  2015年   9篇
  2014年   17篇
  2013年   48篇
  2012年   39篇
  2011年   46篇
  2010年   27篇
  2009年   34篇
  2008年   41篇
  2007年   42篇
  2006年   31篇
  2005年   22篇
  2004年   16篇
  2003年   21篇
  2002年   15篇
  2001年   11篇
  2000年   15篇
  1999年   9篇
  1998年   37篇
  1997年   34篇
  1996年   21篇
  1995年   20篇
  1994年   14篇
  1993年   11篇
  1992年   5篇
  1991年   6篇
  1990年   4篇
  1989年   6篇
  1988年   4篇
  1987年   4篇
  1986年   6篇
  1985年   7篇
  1984年   4篇
  1983年   4篇
  1982年   7篇
  1981年   4篇
  1979年   2篇
  1978年   7篇
  1977年   2篇
  1976年   5篇
  1975年   4篇
  1970年   2篇
排序方式: 共有773条查询结果,搜索用时 15 毫秒
51.
This paper describes the effect of geometry in charge-trap (CT) memory devices. We first theoretically analyze the impact of the curvature radius on the behavior of the gate current in Gate-All-Around devices, and then describe the change to make to planar model in order to fit the cylindrical devices characteristics. This model is used to simulate Nanocrystal and SONOS program, erase and retention behaviors. The dynamics enhancement during program/erase due to the bending of the active region in such cylindrical devices is explained. The scaling perspectives conclude this paper.  相似文献   
52.
An efficient simulation of thermal and mechanical models involved in thermosetting composites forming needs to overcome some numerical difficulties related to: (i) the multi-scale behaviour; (ii) the complex geometries involved needing too many degrees of freedom; (iii) the large time intervals where the solution has to be computed; (iv) the non-linearity of the involved evolution equations; (v) the numerous couplings… In this work, an efficient strategy based on a separated representation is proposed. This method enables to avoid the use of an incremental strategy and can lead to impressive computing time savings especially when the model involves fine meshes and very small time steps. The local non-linear chemical kinetics and its coupling with the global heat balance equation are naturally introduced in the separated representation algorithm. Moreover, the dependence of the thermal conductivity and the specific heat on the temperature and on the reaction advancement degree are also taken into account. Knowing the history of the temperature field, the separated representation is again used to solve the thermo-mechanical problem in order to determine the residual stresses.  相似文献   
53.
An attribute opening is an idempotent, anti-extensive and increasing operator, which removes from an image connected components which do not fulfil a given criterion. When the increasingness property is dropped, we obtain a—more general—attribute thinning. In this paper, we propose efficient grey scale thinnings based on geodesic attributes. Given that the geodesic diameter is time consuming, we propose a new geodesic attribute, the barycentric diameter to speed up the computation time. Then, we give the theoretical error bound between these two attributes, and we note that in practice, the barycentric diameter gives very similar results in comparison with the geodesic diameter. Finally, we present the algorithm with further optimisations, to obtain a 60× speed up. We illustrate the use of these thinnings in automated non-destructive material inspection: the detection of cracks. We discuss the advantages of these operators over other methods such as path openings or the supremum of openings with segments.  相似文献   
54.
55.
The freezing of concentrated colloidal suspensions is a complex physical process involving a large number of parameters. These parameters provide unique tools to manipulate the architecture of freeze-cast materials at multiple length scales in a single processing step. However, we are still far from developing predictive models to describe the growth of ice crystals in concentrated particle slurries. In order to exert reliable control over the microstructural formation of freeze-cast materials, it is necessary to reach a deeper understanding of the basic relationships between the experimental conditions and the microstructure of the growing solid. In this work, we explore the role of several processing variables (e.g., composition of the suspension, freezing rate, and patterning of the freezing surface) that could affect the formulation strategies for the architectural manipulation of freeze-cast materials. We also demonstrate, using freeze-cast lamellar structures, that reducing the lamellar thickness by less than half increases the compressive strength by more than one order of magnitude.  相似文献   
56.
PURPOSE: The effects of chronic chloroquine administration on serum proteins and free amino acids of rabbits and the accompanying ultrastructural changes in the retina were investigated. METHODS: Thirty pigmented rabbits were injected intramuscularly with chloroquine diphosphate (14 mg/Kg bw). Fifteen rabbits served as control. Blood samples drawn after 1, 2, 3, 4, 5, 6 and 12 months were assayed for serum proteins by Bio-analytic kits and horizontal electrophoretic technique. Free amino acids were determined by Beckman analyzer. Central retinal tissue was fixed in 4% glutaraldehyde, embedded in araldite CY212 and sectioned for ultrastructural examination. RESULTS: Histopathologic changes were apparent within three months, initially affecting the pigment epithelium and photoreceptors and later involving the remaining neuroretinal layers. Hypoproteinemia gradually developed mainly due to a sharp drop in albumin and alpha 1 and 2 globulin fractions, inspite of an increase in beta and gamma globulin fractions. The concentration of non-essential amino acids varied considerably from a depletion of taurine, aspartine, glutamine, tryptophan and arginine to an increase of serine, alanine, GABA and ornithine. The most outstanding effect was the disappearance of tyrosine and its return to normal value at the end of the experiment. CONCLUSION: The disturbances in protein pattern and free amino acid levels are an indication of chloroquine toxicity and may be implicated in the retinopathy.  相似文献   
57.
58.
Thirty-six infants born at term who developed hyperbilirubinemia were assessed for developmental status at 2, 4, 6, 9 and 12 months of age according to a mental and psychomotor scale for 0-4 year old. The development quotient (DQ) of infants with hyperbilirubinemia were lower than controls, and the reduction was significant at 2 months of age (P = 0.03). When single component of DQ was compared, it was shown that the DQ score for social behavior was significantly lower in patients at 2 months of age than in control (P = 0.007), and except for motor, other four single DQ scores were lower in patients than in control and the reduction was significant in the DQ scores for adaptability and social behavior (P = 0.05, 0.032, respectively). Furthermore, no significant correlation was found between DQ and serum peak bilirubin value or duration of hyperbilirubinemia. The results indicate that hyperbilirubinemia may have a long term impact on mental development of infants. It is necessary to monitor all infants with hyperbilirubinemia, including full term infants with no severe complication.  相似文献   
59.
Hooded rats with bilateral lesions of the anterior part of the hippocampal formation (HIP), anterior region of the posterior parietal cortex (APC), or posterior region of the posterior parietal cortex (PPC) were compared with controls for their exploration of 5 objects in an open field, habituation of locomotion and object investigation, and response to spatial and nonspatial change. First, all groups displayed habituation of both locomotor and exploratory activity. Second, controls selectively reexplored displaced objects, and APC-lesioned rats reexplored all objects, whereas PPC- and HIP-lesioned rats failed to react to the spatial change. Third, a novel object induced reexploration in all groups. Results are consistent with the roles of the HIP and PPC in spatial information processing. Moreover, the APC and PPC are involved in attentional effortful processing and visuospatial information processing necessary for spatial representation, respectively. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
60.
Between July 1998 and June 1999, 93 lots of broiler chickens distributed on 57 farms were sampled in two abattoirs of the province of Quebec (Canada). A total of 2,325 samples of cecal material were analyzed to determine the prevalence of campylobacters. Biotyping and pulsed-field gel electrophoresis (PFGE) were done on 20% of the Campylobacter isolates to study the distribution within poultry production. Macrorestriction profiles were compared with profiles of 24 Campylobacter strains isolated from sporadic cases of human diarrheic patients in order to evaluate genetic relationships. Approximately 40% of the broiler chickens in 60% of the lots and 67% of the farms were colonized. Biotypes I and II of Campylobacter jejuni were the most prevalent biotypes in poultry and human isolates. The PFGE dendograms revealed a high genetic diversity among poultry isolates, with 49 different genotypes from the 56 positive lots. More than 75% of these lots were colonized by a unique genotype. All positive lots raised simultaneously on the same farm had common genotype(s). Different genotypes were isolated from lots raised at different grow-out periods on a farm. In some cases, identical genotypes were found at different grow-out periods on a farm and also from different farms. Macrorestriction profiles showed that approximately 20% of human Campylobacter isolates were genetically related to genotypes found in poultry. This genetic relationship and the high prevalence of C. jejuni biotypes I and II in poultry indicated that Campylobacter in broiler production of the province of Quebec could be a potential source of hazard for public health.  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