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   158篇
  免费   14篇
  国内免费   3篇
电工技术   1篇
化学工业   37篇
金属工艺   8篇
机械仪表   6篇
建筑科学   3篇
能源动力   8篇
轻工业   7篇
水利工程   1篇
石油天然气   1篇
无线电   11篇
一般工业技术   65篇
冶金工业   18篇
自动化技术   9篇
  2023年   3篇
  2022年   8篇
  2021年   5篇
  2020年   3篇
  2019年   4篇
  2018年   8篇
  2017年   5篇
  2016年   12篇
  2015年   8篇
  2014年   1篇
  2013年   8篇
  2012年   7篇
  2011年   5篇
  2010年   7篇
  2009年   5篇
  2008年   6篇
  2007年   1篇
  2006年   5篇
  2005年   4篇
  2004年   3篇
  2003年   3篇
  2002年   7篇
  2001年   4篇
  2000年   2篇
  1999年   5篇
  1998年   7篇
  1997年   2篇
  1996年   6篇
  1995年   8篇
  1994年   4篇
  1993年   2篇
  1992年   3篇
  1991年   1篇
  1990年   2篇
  1989年   5篇
  1987年   1篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
排序方式: 共有175条查询结果,搜索用时 15 毫秒
41.
BACKGROUND: The optimal material for carotid patch angioplasty after endarterectomy remains uncertain. This study compares the early outcome and recurrent stenosis rates between saphenous vein (SV) and expanded polytetrafluoroethylene (ePTFE) carotid patch angioplasty. METHODS: The results of 421 consecutive carotid endarterectomies performed over a 72-month period were reviewed. Postoperative complications and restenosis rates, defined as > OR = 60% narrowing measured by color flow duplex, were compared. RESULTS: Patch angioplasty was performed with SV in 287 and with ePTFE in 110 cases. Patients who had undergone primary closure (n = 20) or whose form of closure was unknown (n = 4) were excluded. The mean age of patients and length of follow-up was similar between groups. Women were more likely to be patched with ePTFE than were men (36% versus 23%, P = 0.02). One death occurred in each group (0.3% SV, 0.9% ePTFE, P = 0.47), and four strokes occurred in each group (1.4% SV, 3.6% ePTFE, P = 0.22). Cervical hematomas requiring operative evacuation occurred in five SV closures and in three ePTFE closures (1.7% versus 2.7%, P = 0.69). Vein harvest site complications occurred in 6 patients (2%) who had undergone SV patch angioplasty. Recurrent stenosis occurred in 3 patients with SV closure and in 3 patients with ePTFE closure (1.0% versus 2.7%, P = 0.35). The 60-month restenosis rates by life table analysis were 2.6% +/- 2.1% for SV and 10.7% +/- 7.9% for ePTFE (P = 0.17). CONCLUSIONS: The incidence of postoperative complications is similar with SV or ePTFE patch angioplasty; however, vein harvest site complications are avoided with the use of ePTFE. Recurrent stenosis at 5 years occurs infrequently with either SV or ePTFE.  相似文献   
42.
43.
Non-linear consolidation analysis using a finite element formulation based on Biot's consolidation theory has been used to study the behaviour of strip and circular footings resting on an elastic-perfectly plastic soil satisfying the Mohr-Coulomb yield criterion. The initial stress method with a modified Newton-Raphson iterative scheme has been used for this study. Displacement of the footing and pore pressure dissipation in the soil are compared with those of linear analysis. Incorporation of the plastic behaviour of soil increases the consolidation rate and settlement. Effects of flow rule and p0/c ratio on consolidation behaviour have also been reported.  相似文献   
44.
A process to depositγ-MnO2 catalytic oxide onto coconut-shell charcoal substrate is described. Current-potential curves for electroreduction of dioxygen with electrodes fabricated from this catalyzed substrate are obtained in 6M KOH under ambient conditions. The performance of these electrodes is competitive with platinized carbon electrodes. Contribution No. 252 from the Solid State and Structural Chemistry Unit.  相似文献   
45.
46.
The effects of systematic changes in reinforcement size and matrix microstructure on the crack initiation and growth toughness of a 7091 aluminum alloy reinforced with SiC particulates were studied. It is shown that changes in matrix microstructure have a significant effect on both initiation and growth toughness. The effect of reinforcement size on these properties is far less marked. These observations have been related to local microstructural parameters and the nature of the distribution of the reinforcement.  相似文献   
47.
We have designed, fabricated, and tested a compact, transportable, excitation-emission spectrofluorimeter with optical-fiber light delivery and collection for use in rapid analysis of tissues in a clinical setting. This system provides up to eleven different excitation wavelengths, permitting collection of all the corresponding emission spectra in approximately 600 ms. It uses a N(2) laser that pumps a sequence of dyes placed in cuvettes on a rotating wheel. A white-light excitation source permits acquisition of the tissue's diffuse reflectance spectrum on each cycle. Return fluorescence and reflected light are dispersed by a small spectrograph and detected by a photodiode-array detector. The system can collect a single-shot spectrum from biological tissue with a signal-to-noise ratio in excess of 50:1.  相似文献   
48.
This paper is based on the experimental study of twelve slender steel tubular columns of circular sections filled with both plain and fibre reinforced concrete. The specimens were tested under eccentric compression to investigate the effects of fibre reinforced concrete on the strength and behaviour of slender composite columns. The slenderness ratio was considered to be the main test parameter. Hollow steel sections of similar specimens were also tested as reference columns. The test results were illustrated by load-deflection and load-strain curves. Various characteristics such as strength, stiffness, ductility, energy absorption capacity and failure mode are discussed. Interpretation of the experimental results indicates that the use of fibre reinforced concrete as infill material has a considerable effect on the strength and behaviour of slender composite columns.  相似文献   
49.
50.
Fish and water samples were collected from various randomly situated sampling sites in two tropical man‐made lakes, Peechi and Pothundi reservoirs, in South India. The fish samples collected during 2014 to 2015 were taxonomically identified and the fish diversity indices of these reservoirs evaluated. The water samples collected were analysed for such environmental variables as pH, electrical conductivity, dissolved oxygen concentration, alkalinity, hardness, chlorophyll and nutrient concentrations. T‐tests indicated significant difference in both the fish diversity and environmental variables between these two reservoirs. The Pearson correlation test identified electrical conductivity as a highly correlated environmental variable to the ichthyodiversity index in Peechi and Pothundi reservoirs, with coefficients of 0.939 and 0.7012, respectively. Principal co‐ordinate analysis also was conducted on the variables to identify the best combination of variables subjective to the particular sampling site influencing the fish diversity. The analyses explained 72.8% of the total variations for Peechi reservoir, which was represented with eigenvalues of 7.53 and 3.393, respectively, for the first two dimensions. A similar analysis of Pothundi reservoir produced eigenvalues 7.05 and 3.01, respectively, for the first two dimensions, explaining 67.1% of the total inertia. The individual factor maps (IFM‐I and IFM‐II) for Peechi and Pothundi reservoirs identified a high diversity at sampling site 3 in Peechi reservoir, and a similar finding for sites 3 and 7 in Pothundi reservoir, being related to the interactions with other environmental variables, which were greatly influenced by the predominance of macrophytes. The latter is a characteristic of rainfed tropical reservoirs, with special reference to the native fish diversity and environmental variables. The findings of this study suggest management decisions for any aquatic system may be considered after prior assessment of environmental variables and the ichthyodiversity index of the indicated waterbody.  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