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   223篇
  免费   3篇
化学工业   96篇
金属工艺   2篇
机械仪表   4篇
建筑科学   4篇
能源动力   8篇
轻工业   19篇
无线电   37篇
一般工业技术   32篇
冶金工业   10篇
自动化技术   14篇
  2024年   2篇
  2023年   1篇
  2022年   16篇
  2021年   20篇
  2020年   4篇
  2019年   3篇
  2018年   1篇
  2017年   5篇
  2016年   2篇
  2015年   3篇
  2014年   6篇
  2013年   18篇
  2012年   5篇
  2011年   11篇
  2010年   5篇
  2009年   7篇
  2008年   8篇
  2007年   2篇
  2006年   8篇
  2005年   3篇
  2004年   2篇
  2003年   5篇
  2002年   5篇
  2001年   3篇
  2000年   1篇
  1999年   3篇
  1998年   3篇
  1997年   4篇
  1996年   4篇
  1995年   5篇
  1994年   5篇
  1993年   3篇
  1992年   7篇
  1991年   13篇
  1990年   2篇
  1989年   6篇
  1988年   4篇
  1987年   2篇
  1986年   2篇
  1985年   2篇
  1983年   1篇
  1981年   1篇
  1979年   1篇
  1978年   1篇
  1976年   4篇
  1975年   1篇
  1974年   2篇
  1973年   2篇
  1972年   1篇
  1969年   1篇
排序方式: 共有226条查询结果,搜索用时 15 毫秒
1.
A review is carried out on how queueing network models with blocking have been applied so far into the performance evaluation and prediction of Software Architectures (SA). Queueing network models with finite capacity queues and blocking have recently been introduced and applied as more realistic models of systems with finite capacity resources and population constraints. Queueing network models have been often adopted as models for the evaluation of software performance. Starting from our own experience, we observe the need of a more accurate definition of the performance models of SA to capture some features of the communication systems. We consider queueing networks with finite capacity and blocking after service (BAS) to represent some synchronization constraints that cannot be easily modeled with queueing network models with infinite capacity queues. We investigate the use of queueing networks with blocking as performance models of SA with concurrent components and synchronous communication. Queueing theoretic analysis is used to solve the queueing network model and study the synchronous communication and performance of concurrent software components. Our experience is supported by other approaches that also propose the use of queueing networks with blocking. Directions for future research work in the field are included.  相似文献   
2.
Ion-beam sputter-deposited alloy films of Co/sub 74/Fe/sub 6/B/sub 15/Si/sub 5/ and Fe/sub 75/Ni/sub 5/B/sub 15/Si/sub 5/ were examined for their magnetic and structural properties. Films were characterized by ferromagnetic resonance, vibrating sample magnetometry, and extended X-ray absorption fine structure (EXAFS) analysis. Using atomic parameters deduced from EXAFS modeling and fitting procedures, magnetic properties were calculated with no adjustable parameters. Correlation between perpendicular FMR measurements and EXAFS first-shell modeling suggests a low-temperature formation of cobalt-borides in the Co/sub 74/Fe/sub 6/B/sub 15/Si/sub 5/ alloy. Annealed Fe/sub 75/Ni/sub 5/B/sub 15/Si/sub 5/ samples did not display evidence of structural and/or magnetic instabilities until the onset of long-range crystallization near T/sub ann/=400 degrees C.<>  相似文献   
3.
Sorption and diffusion of dichloromethane vapor were measured in atactic polystyrene films, obtained with different cooling conditions and after controlled aging times at different temperatures. The diffusional behavior is characterized by three zones, depending on temperature and penetrant activity. In Zone I, at low activity, the diffusion coefficient is independent of vapor concentration; Zone II is characterized by concentration-dependent diffusion, whereas in Zone III structural transformations are possible. The study of diffusion at three temperatures allowed building of a temperature-penetrant concentration diagram, which is very useful to visualize the different zones of behavior. The aging at room temperature has no effect on the curve of sorption as a function of vapor activity, whereas it determines two effects on the diffusion: a decrease of the zero concentration diffusion coefficient and a more and more anomalous behavior with the aging time. The aging at 70°C produces the same effects on the diffusion behavior as the aging at room temperature; in addition, a decrease sorption is observed at low penetrant activity. The possible presence of ordered domains, impermeable to the vapor, in the samples stored at 70°C, was suggested on the basis of sorption results.  相似文献   
4.
The drawing behavior of two polypropylene films of different structures was analyzed. The two films differ as a consequence of different quenching conditions. At low temperature, a biphasic smectic-amorphous system was obtained, while quenching at 100°C produced a biphasic crystalline-amorphous system. The drawing of samples was carried out at 110°C at which temperature the smectic phase is not stable and is transformed into the crystalline α-form. The initial structure affects the drawing behavior and the properties of the drawn samples. The mechanical, optical, and X-ray analyses clearly show that high molecular orientation is achieved at lower deformations in the initially smectic sample. In particular, the amorphous phase is highly oriented, inducing higher axial elastic modulus.  相似文献   
5.
Variational multiscale large-eddy simulations (VMS–LES) of the flow around a circular cylinder are carried out at different Reynolds numbers in the subcritical regime, viz. Re = 3900, 10,000 and 20,000, based on the cylinder diameter. A mixed finite-element/finite-volume discretization on unstructured grids is used. The separation between the largest and the smallest resolved scales is obtained through a variational projection operator and finite-volume cell agglomeration. The WALE subgrid scale model is used to account for the effects of the unresolved scales; in the VMS approach, it is only added to the smallest resolved ones. The capability of this methodology to accurately predict the aerodynamic forces acting on the cylinder and in capturing the flow features are evaluated for the different Reynolds numbers considered. The sensitivity of the results to different simulation parameters, viz. agglomeration level and numerical viscosity, is also investigated at Re = 20,000.  相似文献   
6.
This paper presents a novel model for the removal of semi-transparent blotches on the digitized copy of sepia archive photographs. As these defects cannot be successfully eliminated by conventional interpolation methods, a proper combination of a novel visual distortion and multiresolution analysis is used for performing user-independent detection and restoration. Extensive experimental results and comparative studies show the potential of the proposed model in terms of visual quality and computational complexity.  相似文献   
7.
We report on the use of a fluorinated imidazolium ionic liquid as a source of iodide ions in solvent-based electrolytes for DSSCs. Efficient dye regeneration and fast charge transport in the fluorinated electrolyte result in an overall improvement of the device performances compared to conventional hydrogenated ionic liquids.  相似文献   
8.
Celiac disease (CD) is a type of inflammatory chronic disease caused by nutrients such as gliadin that induce a TC (T cell)-mediated response in a partially known genetical background in an environment predisposed to inflammation, including viruses and food. Various experimental and clinical observations suggest that multiple agents such as viruses and bacteria have some common, inflammatory pathways predisposing individuals to chronic inflammatory diseases including celiac disease (CD). More recently, a Western diet and lifestyle have been linked to tissue inflammation and increase in chronic inflammatory diseases. In CD, the gliadin protein itself has been shown to be able to induce inflammation. A cooperation between viruses and gliadin is present in vitro and in vivo with common mechanisms to induce inflammation. Nutrients could have also a protective effect on CD, and in fact the anti-inflammatory Mediterranean diet has a protective effect on the development of CD in children. The possible impact of these observations on clinical practice is discussed.  相似文献   
9.
Resveratrol (RSV) is a natural compound that displays several pharmacological properties, including anti-cancer actions. However, its clinical application is limited because of its low solubility and bioavailability. Here, the antiproliferative and anti-inflammatory activity of a series of phenylacetamide RSV derivatives has been evaluated in several cancer cell lines. These derivatives contain a monosubstituted aromatic ring that could mimic the RSV phenolic nucleus and a longer flexible chain that could confer a better stability and bioavailability than RSV. Using MTT assay, we demonstrated that most derivatives exerted antiproliferative effects in almost all of the cancer cell lines tested. Among them, derivative 2, that showed greater bioavailability than RSV, was the most active, particularly against estrogen receptor positive (ER+) MCF7 and estrogen receptor negative (ER-) MDA-MB231 breast cancer cell lines. Moreover, we demonstrated that these derivatives, particularly derivative 2, were able to inhibit NO and ROS synthesis and PGE2 secretion in lipopolysaccharide (LPS)-activated U937 human monocytic cells (derived from a histiocytoma). In order to define the molecular mechanisms underlying the antiproliferative effects of derivative 2, we found that it determined cell cycle arrest at the G1 phase, modified the expression of cell cycle regulatory proteins, and ultimately triggered apoptotic cell death in both breast cancer cell lines. Taken together, these results highlight the studied RSV derivatives, particularly derivative 2, as promising tools for the development of new and more bioavailable derivatives useful in the treatment of breast cancer.  相似文献   
10.
The catalytic activity of a lysozyme-based oenological preparation toward the specific substrates i) glycol chitosan, as a non-cellular synthetic substrate, and ii) Oenococcus oeni, as a microbial substrate for muramidase activity, was investigated in wine-like acidic medium (tartaric buffer, pH 3.2). The good reproducibility and reliability of results revealed that both substrates are useful for lysozyme kinetics studies. Both the chitinolytic and muramidase activity of lysozyme were affected by uncompetitive substrate inhibition. However, the O. oeni effect occurred at very high concentration with respect to the typical wine bacterial content, even when microbial population reaches its maximum growth level during malolactic fermentation. The optimum pH and temperature for lysozyme activity were very far from the usual wine handling conditions, but residual enzyme activity was observed at pH 3.2 and 20°C, confirming that the oenological application of lysozyme is a useful practice.  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