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   377篇
  免费   7篇
电工技术   11篇
化学工业   67篇
金属工艺   12篇
机械仪表   8篇
建筑科学   7篇
能源动力   17篇
轻工业   16篇
水利工程   6篇
无线电   43篇
一般工业技术   89篇
冶金工业   85篇
原子能技术   4篇
自动化技术   19篇
  2021年   2篇
  2020年   1篇
  2019年   6篇
  2018年   3篇
  2017年   4篇
  2016年   7篇
  2015年   5篇
  2014年   9篇
  2013年   22篇
  2012年   17篇
  2011年   17篇
  2010年   11篇
  2009年   10篇
  2008年   15篇
  2007年   5篇
  2006年   17篇
  2005年   10篇
  2004年   5篇
  2003年   9篇
  2002年   16篇
  2001年   10篇
  2000年   13篇
  1999年   14篇
  1998年   34篇
  1997年   25篇
  1996年   13篇
  1995年   11篇
  1994年   12篇
  1993年   7篇
  1992年   2篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1987年   3篇
  1986年   2篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1978年   2篇
  1977年   1篇
  1976年   5篇
  1974年   4篇
  1973年   2篇
  1971年   1篇
  1970年   1篇
  1969年   2篇
  1968年   1篇
排序方式: 共有384条查询结果,搜索用时 15 毫秒
1.
Characteristic power-law dependence of junction conductance on temperature was confirmed at low temperatures fora,b-axis oriented Au/PrBa2Cu3O7−x /YBa2Cu3O7−y junctions with a PrBa2Cu3O7−x layer thinner than 30 nm, indicating that current transport via a small number of localized states was predominant. The radius and the density of the localized states were estimated to be 1.1 nm and 5.0x1019 eV−1 cm−3, respectively. Transport measurement at 1.7 K in a magnetic field of up to 6 T revealed no indication of on-site Coulomb repulsion of electrons in the localized states. These results support the possibility of resonant tunneling of Cooper pairs in superconductor-insulator-superconductor junctions with a thin PrBa2Cu3O7−x tunnel barrier.  相似文献   
2.
To evaluate right atrial (RA) contractile performance in patients with myocardial infarction, we validated a cineangiographic method of RA volume measurement, and investigated RA volume change in 'normal' individuals and patients with a previous myocardial infarction. Sixteen silicone rubber RA casts made from human cadavers were filmed in the postero-anterior and left lateral projections. The cast volumes calculated following Simpson's rule were in good agreement with those measured by water replacement (r = 0.992, P < 0.01). At cardiac catheterization, biplane RA cineangiography was performed in 19 'normal' individuals (N group), in 14 patients with a previous antero-septal infarction (AMI group) and in seven patients with a previous inferior infarction (IMI group). The RA volume-time curve was constructed at 20-40 ms intervals for one cardiac cycle. RA volume at the beginning of the atrial contraction (RAVd), which was defined as the 'preload' of the RA, tended to be larger in both the AMI and IMI groups compared with 'normal' individuals. The RA ejection volume was significantly larger in both the AMI (18.4 +/- 2.1 ml.m-2, P < 0.01) and IMI groups (19.4 +/- 2.8, P < 0.01) than in the N group (14.5 +/- 1.9), even for a comparable level of RAVd (range from 26 to 36 ml.m-2) (18.6 +/- 2.1, P < 0.01, 18.2 +/- 2.0, P < 0.01, 14.7 +/- 1.9, respectively). These results suggest that RA contraction increases in patients with myocardial infarction by increasing both the 'preload' and 'contractility' of the RA.  相似文献   
3.
Using the TOXI-LAB drug detection system, emergency toxicological screening was performed in autopsy cases and emergency cares. In 280 autopsy cases (male 182 cases 65%, female 98 cases 35%), drug positive cases were 28 cases of male (15%) and 24 cases of female (24%). The age groups which showed higher rate of drug positive cases were 10s-40s in male (approximately 20%) and 20s in female (67%). In the 238 cases of emergency care (male 129 cases 54%, female 104 cases 44%, unknown 5 cases 2%), drugs were positive in 29 cases of male (22%) and 32 cases of female (30%). The age groups which showed relatively higher rate of drug positive cases were 40s in male (64%), 20s (71%) and 30s (89%) in female. Forty-four different kinds of drugs were detected in TOXI-LAB positive cases, in which the psychotropic drugs and the sedative-hypnotic drugs amounted to approximately 70%. Methamphetamine and amphetamine, which were the main abused drugs showing a socially important problem, were detected in total 15 cases. TOXI-LAB was based on thin-layer chromatography (TLC); however, from the extraction to development, coloration and detection have been accelerated (about 50 min) and simplified. In order to perform the forensic toxicological practice in Japan, it becomes more useful that TOXI-LAB is used in autopsy cases and emergency cares, if the drugs, which have caused poisoning cares in Japan, are added to TOXI-LAB. The present study describes the advantage and problem of TOXI-LAB drug detection system through demonstrating the practical cases of autopsy cases and emergency cares.  相似文献   
4.
5.
To estimate the risk factors for intellectual dysfunction and examine its prognosis in a community-residing (non-institutionalized) elderly population, a randomly selected sample of 1,473 elderly people aged 65 years and over living in S city, Osaka Prefecture, was studied in October 1992, and data were obtained from 1,383, a response rate of 93.9%. A cohort of 1,383 was followed for 42 months and follow-up was completed for 1,300 (94.0%). The main results were as follows: 1) The prevalence of intellectual dysfunction did not differ significantly between sexes, and there was an increasing prevalence of intellectual dysfunction with age in both sexes. The prevalence of severe intellectual dysfunction was found to increase highly at age 85 and over. 2) By univariate analysis, odds ratios for age older than 75 years, low Activities of Daily Living (ADL), urinary and fecal incontinence, and no participation in social activities were significantly higher than 1 in any level of mild, moderate, and severe intellectual dysfunction. In the multivariate analysis using logistic regression, age older than 75 years and urinary and fecal incontinence showed significant higher odds ratios than 1 for severe intellectual dysfunction, and low ADL and treatment for hypertension also showed significant higher odds ratios than 1 for moderate intellectual dysfunction. 3) From analysis using the Kaplan-Meier method, the cumulative survival rates decreased with a decline in intellectual functioning in both age groups of 65-74 and 75 years and older. 4) Application of the Cox proportional hazards model resulted in adjusted hazard ratio for severe intellectual dysfunction of 1.79 (95% confidence interval, 1.02-3.12), controlling for other factors such as sex, age, general health status, incontinence and social activities.  相似文献   
6.
STATEMENT OF PROBLEM: Improved dental stone has been widely used for producing dies for the fabrication of restorations with the lost-wax technique. Improved dental stone is used for several reasons, but it is selected most often because of its reasonable cost, ease of use, and ability to produce consistent results. PURPOSE: This study evaluated the ability of an epoxy resin die material and a type IV dental stone to dimensionally reproduce a custom-fabricated metal die. MATERIAL AND METHODS: Dies were fabricated and measurements were made from three reference lines. Measurements were repeated three times for the master die and for the specimen dies. A mean measurement and percent relative change for each dimension was calculated. RESULTS: A significant difference in the relative change for die height was found between the groups studied (p < 0.003). CONCLUSIONS: This epoxy die system will provide a degree of dimensional accuracy comparable to gypsum when used with addition silicone impression material.  相似文献   
7.
It was determined that the discharge in the vicinity of ribs should be intensified to obtain low‐voltage, high‐luminous efficacy, and high module efficiency. One possible way is to increase the space between ribs and the discharge surface. Even if the amount of space increases by only 2 or 3 µm, it still results in low discharge voltage, large discharge current, and high luminous efficacy. For that reason it might be important to control the micron‐sized particles included in the MgO crystal dispersed layers. Another preferable way is to use ribs with a low electric permittivity (ε) that are represented by porous ribs. Moreover, low‐ε ribs diffuses the high‐energy spots in plasma, resulting in a high luminous efficacy. They feature a significantly lower sustain voltage and a smaller parasitic capacitance as well to facilitate a help high module efficiency. Also, highly porous ribs are expected to increase their practical use in aspects of mechanical strength and impurity gas exhaustion.  相似文献   
8.
9.
Using shorter wavelength for exposure light is one way to achieve high resolution while keeping sufficient depth of focus. We show exposure results for high resolution to confirm the effect of deep UV exposure light. With deep UV light, 1.2‐µm line and space pattern and 1.8‐µm contact hole pattern are resolved while keeping sufficient depth of focus.  相似文献   
10.
A distributed system is said to be self-stabilizing if it converges to safe states regardless of its initial state. In this paper we present our results of using symbolic model checking to verify distributed algorithms against the self-stabilizing property. In general, the most difficult problem with model checking is state explosion; it is especially serious in verifying the self-stabilizing property, since it requires the examination of all possible initial states. So far applying model checking to self-stabilizing algorithms has not been successful due to the problem of state explosion. In order to overcome this difficulty, we propose to use symbolic model checking for this purpose. Symbolic model checking is a verification method which uses Ordered Binary Decision Diagrams (OBDDs) to compactly represent state spaces. Unlike other model checking techniques, this method has the advantage that most of its computations do not depend on the initial states. We show how to verify the correctness of algorithms by means of SMV, a well-known symbolic model checker. By applying the proposed approach to several algorithms in the literature, we demonstrate empirically that the state spaces of self-stabilizing algorithms can be represented by OBDDs very efficiently. Through these case studies, we also demonstrate the usefulness of the proposed approach in detecting errors  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