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   216篇
  免费   5篇
  国内免费   2篇
电工技术   6篇
化学工业   40篇
金属工艺   2篇
机械仪表   4篇
建筑科学   6篇
矿业工程   1篇
能源动力   5篇
轻工业   6篇
水利工程   3篇
无线电   39篇
一般工业技术   33篇
冶金工业   58篇
原子能技术   1篇
自动化技术   19篇
  2022年   1篇
  2021年   1篇
  2020年   2篇
  2019年   2篇
  2018年   2篇
  2016年   2篇
  2015年   4篇
  2014年   1篇
  2013年   11篇
  2012年   12篇
  2011年   11篇
  2010年   11篇
  2009年   4篇
  2008年   4篇
  2007年   6篇
  2006年   7篇
  2005年   7篇
  2004年   4篇
  2003年   8篇
  2002年   6篇
  2001年   5篇
  2000年   6篇
  1999年   11篇
  1998年   24篇
  1997年   9篇
  1996年   5篇
  1995年   3篇
  1994年   6篇
  1993年   13篇
  1992年   3篇
  1991年   3篇
  1990年   2篇
  1989年   3篇
  1987年   3篇
  1986年   2篇
  1985年   4篇
  1984年   2篇
  1983年   1篇
  1980年   2篇
  1976年   3篇
  1975年   2篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1964年   1篇
  1956年   1篇
排序方式: 共有223条查询结果,搜索用时 15 毫秒
31.
OBJECTIVE—To compare the tobacco use profile of recruits with that of military personnel on active duty to determine whether the military environment in some way induces service members to initiate tobacco use.
DESIGN AND SETTING—Cross-sectional survey of United States armed forces active duty and recruit personnel in 1994-95.
SUBJECTS—2711 military recruits and 4603 military personnel on active duty.
MAIN OUTCOME MEASURES—Comparative cigarette smoking and smokeless tobacco use prevalence between recruits and personnel on active duty controlling for age, sex, and race. Impact of demographic factors on the odds of smoking or using smokeless tobacco.
RESULTS—Increases in tobacco use in American military personnel occurred exclusively in men. The highest tobacco use resided with white men on active duty (43% cigarette smoking; 24% smokeless tobacco use) and represents a doubling of tobacco use seen among white male recruits. Among non-white men, tobacco use increased 2-4 times between recruits and personnel on active duty.
CONCLUSIONS—Efforts to reduce tobacco use by American military personnel on active duty should focus more on discouraging the initiation of tobacco use.


Keywords: tobacco use; military personnel; United States  相似文献   
32.
The ability of two coupled oscillators to synchronize depends critically on the coupling network. Previous analyses have accurately predicted the performance of quasi-optical microwave oscillator arrays for both weak and strong coupling, but have been limited to coupling networks with bandwidths considerably larger than the locking bandwidths of the oscillators. In this paper, the authors develop a method for deriving a suitable system of nonlinear differential equations describing the oscillator amplitude and phase dynamics using a generalization of Kurokawa's method. The method is applied to the case of two Van der Pol oscillators coupled through a resonant network for a wide range of coupling strengths and bandwidths. Simple approximate formulas are developed for the size of the frequency locking region as functions of the basic circuit parameters  相似文献   
33.
Global warming and the resource depletion induced discussions on sustainable developments within the construction sector. Also the rapid urbanization in subtropical regions is becoming one of the most important global issues. Appropriate measures must be taken in such developments to avoid further damage to the environment. In this study, the heat and moisture balance simulation of building with a sustainable building envelope system for subtropical climate was proposed. In the moisture balance simulation the moisture buffering by the interior materials was taken into account. The prediction of moisture buffer value (MBV) of the interior finishing materials was attempted and validated by measurements. Subsequently, the whole building calculation was carried out and the contribution of the moisture buffering to the indoor comfort and energy consumption was investigated. The MBVs of the mineral-based materials were predicted with high accuracy. However, that of wood-based composite was much higher than the experimental value. In order to create a more accurate model, nonlinear moisture conductance should be accounted when modeling wood-based materials. The heating and cooling demand of a test house was 9.4 kWh/m2 and 14.5 kWh/m2, respectively. It was concluded that the utilization of the building envelope system has a high potential to provide sustainable houses in subtropical regions. In order to enhance both energy efficiency and indoor comfort of buildings in subtropical regions, there still is a strong need to develop a holistic method to find the optimum building design considering not only moisture buffering but also all the relevant factors. The presented model will be validated by in-situ measurements in the near future.  相似文献   
34.
This paper investigates a methodology for the optimization of wet granulation processes in planetary mixers. A model formulation was granulated in a planetary mixer (two different bowl sizes). The wet masses were characterized by their bulk density and consistency (as measured by mixer torque rheometry), and the feasibility of scale-up from one mixer bowl to the other was studied using a dimensionless numbers approach for the estimation of the power consumption at the granulation end point. Both bowls gave the same dimensionless power relationships (a relationship between the power number, Reynolds number, Froude number, and bowl fill ratio), which could therefore be used for calculating the power consumption level when the wet mass achieves its target values of density and consistency, i.e., the point at which granulation should be stopped. It was also shown that batches granulated in different conditions (batch size, blade speed) in two planetary mixers, but presenting similar wet mass characteristics (bulk density and consistency) led to dry granules of similar properties: granule size distribution, density, friability, and flow. This work suggests that it is possible to characterize the wet mass by only two parameters which describe the quality of the downstream granules. The scale-up procedure based on the use of dimensionless numbers was found to be applicable to planetary mixers, provided they give one common dimensionless power relationship.  相似文献   
35.
The excursion resistance between the canine flexor digitorum profundus tendon and A2 pulley was compared after pulley reconstruction using tendon grafts of either intrasynovial or extrasynovial origin at 10 days, 3 weeks, and 6 weeks after surgery. The changes over time in the underlying flexor digitorum profundus tendon after pulley reconstruction were also evaluated. The excursion resistance for both types of pulley reconstruction was significantly greater than that of the control group at all time periods. The excursion resistance of the extrasynovial tendon graft reconstruction was greater than that of intrasynovial pulley reconstruction at all time periods. In conclusion, pulley reconstruction with intrasynovial tendon grafts may facilitate tendon gliding after surgery.  相似文献   
36.
From February to June in 1996, there were 47,800 students for health examination in Taichung City, Taiwan. The population consisted of the first and fourth graders of primary schools and the first grader of junior high schools. We selected 3,452 healthy students for further study by two stage sampling. In this report, 52.5% of the students were boys, and 47.5% of the students were girls. The mean age of students was 9.9 +/- 2.4 years. Girls at age 7 and age 10 had higher activity of alkaline phosphatase than boys at the same age. The peak of alkaline phosphatase activity in girls occurred at age 10. Alkaline phosphatase activity was significantly related to weight-length index by multiple regression analysis (p < 0.05). Although clinical application as an obesity factor still needs further investigation, in the future it may be well to routinely check this enzyme when assessing childhood obesity.  相似文献   
37.
38.
Although most alcoholic subjects show little autonomic dysfunction, severe alcoholic subjects may have pathological changes in autonomic nerves. We asked if respiratory sinus arrhythmia amplitude (RSA), an index of vagal cardiac control, is decreased in alcoholism and, if so, whether the decrease is reversed with abstinence. RSA was assessed in 17 normotensive alcoholic subjects (A) at 1, 4, 12, and 24 wk of abstinence after detoxification and at similar intervals in 17 controls (C) matched for age, race, and gender. Subjects were studied in both supine and seated positions while breathing in a prescribed deep (> 50% vital capacity) and slow (5-7/min) pattern. Mean heart rate (HR) was determined over 30 s from the electrocardiogram; RSA (the difference between maximum and minimum instantaneous HRs after inspiratory onset) was determined from 10 consecutive breaths. In C, both HR (supine: 61.5 +/- 2.2 beats/min; seated: 71.3 +/- 1.7 beats/min; P < 0.002) and RSA (supine: 22.5 +/- 1.0 beats/min; seated: 28.4 +/- 1.4 beats/min; P < 0.003) were higher when seated than when supine, but neither HR nor RSA varied over 24 wk. At week 1 of abstinence, HRs for A were higher than those for C (supine: 74.2 +/- 2.3 beats/min, P < 0.001; seated: 83.2 +/- 2.7 beats/min, P < 0.003), but by week 24, both seated and supine values returned to control levels. RSA in A at week 1, was only one-half that of C (supine: 11.1 +/- 1.4 beats/min, P < 0.001; seated: 14.7 +/- 1.9 beats/min, P < 0.001) and independent of body position.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
39.
Programming languages have traditionally had more data types than database systems. The flexibility of abstract types could make a database system more useful in supporting application development. Abstract types allow users to think about and manipulate data in terms and structures that they are familiar with. This paper proposes that databases have a type system interface and describes a representation of a type system in terms of relations. The type system model supports a variety of programming language constructs, such as user-defined parameterized data types and user-defined generic operations. The efficiency of the type system is compared to the access time of the database system.  相似文献   
40.
Escherichia coli KO11 was previously constructed to produce ethanol from acid hydrolysates of hemicellulose (pentoses and hexoses) by the chromosomal integration of Zymomonas mobilis genes encoding pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adhB). Klebsiella oxytoca P2 was constructed in an analogous fashion for the simultaneous saccharification and fermentation of cellulose and contains PTS enzymes for cellobiose. In this study, KO11 was further engineered for the fermentation of cellulose by adding the K. oxytoca casAB genes encoding Enzyme IIcellobiose and phospho-beta-glucosidase. Although the two K. oxytoca genes were well expressed in cloning hosts such as DH5 alpha, both were expressed poorly in E. coli KO11, a derivative of E. coli B. Spontaneous mutants which exhibited more than 15-fold-higher specific activities for cellobiose metabolism were isolated. The mutations of these mutants resided in the plasmid rather than the host. Three mutants were characterized by sequence analysis. All contained similar internal deletions which eliminated the casAB promoter and operator regions and placed the lacZ Shine-Dalgarno region immediately upstream from the casA Shine-Dalgarno region. KO11 harboring mutant plasmids (pLOI1908, pLOI1909, or pLOI1910) rapidly fermented cellobiose to ethanol, and the yield was more than 90% of the theoretical yield. Two of these strains were used with commercial cellulase to ferment mixed-waste office paper to ethanol.  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