首页 | 官方网站   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   943篇
  免费   50篇
  国内免费   5篇
工业技术   998篇
  2024年   2篇
  2023年   22篇
  2022年   29篇
  2021年   41篇
  2020年   18篇
  2019年   29篇
  2018年   36篇
  2017年   45篇
  2016年   38篇
  2015年   28篇
  2014年   33篇
  2013年   77篇
  2012年   42篇
  2011年   72篇
  2010年   42篇
  2009年   32篇
  2008年   35篇
  2007年   39篇
  2006年   25篇
  2005年   17篇
  2004年   14篇
  2003年   29篇
  2002年   14篇
  2001年   8篇
  2000年   15篇
  1999年   16篇
  1998年   31篇
  1997年   15篇
  1996年   12篇
  1995年   9篇
  1994年   26篇
  1993年   7篇
  1992年   9篇
  1991年   7篇
  1990年   8篇
  1989年   5篇
  1988年   9篇
  1987年   12篇
  1986年   6篇
  1985年   2篇
  1984年   10篇
  1983年   5篇
  1982年   3篇
  1981年   2篇
  1980年   3篇
  1977年   2篇
  1976年   6篇
  1973年   3篇
  1972年   3篇
  1964年   1篇
排序方式: 共有998条查询结果,搜索用时 15 毫秒
1.
Many occupations require workers to stand for long periods of time without proper interventions, which causes discomfort in the back and lower limbs. Therefore, this study aims to assess the effectiveness in alleviating body muscle discomfort during prolonged standing through the use of a calf massager. This study was conducted among male workers at a manufacturer with production line workers and the list was obtained from the HR Department and simple random sampling was done by number categorization. A total of 100 respondents (50 respondents for both the control and the experimental groups) participated in this study. The experiment took place in a room with a similar setup for the production line. Each respondent was requested to perform the simulated task for 2 hr. For the experimental group, the calf massager was turned on every 15 min. At every 15‐min interval after turning on the calf massager, respondents from both groups were required to evaluate their discomfort level on a Borg's scale CR‐10 questionnaire. The results showed that the level of body discomfort among respondents in the experimental group reduced (20–30%) compared with that of the control group. Multivariate analysis results revealed that the discomfort rating for the lower back, knees, thighs, calves, and feet was significantly lower (p < .05) among the experimental group compared with the control group. For lower body parts, the lower back region was statistically significant (p < .05) at the 90th, 105th, and 120th min; the thigh region was statistically significant (p < .05) at the 120th min; the knee region was statistically significant (p < .05) at the 105th and 120th min; the calf region was statistically significant (p < .05) at all minute intervals except the 15th and 45th min, while the feet region, was statistically significant at the 105th and 120th min. Therefore, this study indicates that calf massage treatment is capable of reducing body muscle discomfort during prolonged standing and highlights the significance of calf massage.  相似文献   
2.
The electrochemical reduction of carbon dioxide (CO2) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO2 to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO2 to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO2 in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.  相似文献   
3.
4.
A 9-μm cutoff 640×486 snap-shot quantum well infrared photodetector (QWIP) camera has been demonstrated. The performance of this QWIP camera is reported including indoor and outdoor imaging. The noise equivalent differential temperature (NEΔT) of 36 mK has been achieved at 300 K background with f/2 optics. This is in good agreement with expected focal plane array sensitivity due to the practical limitations on charge handling capacity of the multiplexer, read noise, bias voltage, and operating temperature  相似文献   
5.
6.
In the last three years or so we at Enterprise Platforms Group at Intel Corporation have been applying formal methods to various problems that arose during the process of defining platform architectures for Intel's processor families. In this paper we give an overview of some of the problems we have worked on, the results we have obtained, and the lessons we have learned. The last topic is addressed mainly from the perspective of platform architects.  相似文献   
7.
The degradation problem of petroleum products arises since hydrocarbon acts as an excellent food source for a wide variety of microorganisms. Microbial activity leads to unacceptable level of turbidity, corrosion of pipeline and souring of stored product. The present study emphasizes the role of Bacillus cereus ACE4 on degradation of diesel and its influence on corrosion of API 5LX steel. A demonstrating bacterial strain ACE4 was isolated from corrosion products and 16S rRNA gene sequence analysis showed that it has more than 99% similarity with B. cereus. The biodegradation and corrosion studies revealed that B. cereus degraded the aliphatic protons and aromatic protons in diesel and is capable of oxidizing ferrous/manganese into oxides. This is the first report that discloses the involvement of manganese oxidizer B. cereus ACE4 on biodegradation of diesel and its influence on corrosion in a tropical country pipeline.  相似文献   
8.
The authors present a multiserver, first-come first-served queuing system that alternates between two modes of system operation. In one mode, all s servers are available, and in the other mode, only s-1 servers are available for serving the customers. This is due to breakdown of one of the servers. The random variables representing the system with s servers and s-1 servers have exponential distributions. In such a system, the steady-state birth/death equations are coupled because of the two modes of operation. A recursive solution is presented for computing the steady-state probabilities of such a system. Once these probabilities are known, the performance measures of interest can be easily obtained. Two practical examples validate the results and show the utility of this method. A distinct advantage of the recursive technique is that it is much faster and requires much less memory than the existing nonrecursive techniques. In a bilevel situation, the system performance measures are always bounded by two independent queuing systems with s and s-1 servers. A procedure has been outlined for extension to multiple modes of system operation  相似文献   
9.
Nanocrystalline orthoferrite powders were synthesised at low temperatures by employing an aqueous sol–gel process. Colloidal sols and water re-dispersible gels of orthoferrite precursors were prepared by room-temperature processing of inexpensive metal salts. The average diameter (Zav) of the precursor particles was in the size range from 4 to 7 nm; the diameters had a narrow size distribution. Water re-dispersible translucent gel monoliths were obtained by concentrating the aqueous sols followed by drying them under reduced pressure (10−2 Torr) at room temperature. The sol–gel transition was found to be completely reversible. Nanocrystalline fine powders of orthoferrites of general formula, LnFeO3 (Ln = La, Sm, Gd, Dy, Er, Yb and Y) having a crystallite size of about 25 nm were prepared by heating the gel precursors at 650–700 °C in air. Powder X-ray diffraction and thermogravimetry, respectively, were employed to identify perovskite phase formation and delineate thermal events that lead to gel to crystallite conversion. Magnetic measurements were carried out on the resultant powders at room temperature and down to 40 K. Nanocrystalline orthoferrite powders exhibited weak ferromagnetic behaviour, and reduced magnetic moments.  相似文献   
10.
Propenylbenzenes and cinnamic acid derivatives yield correspondingly substituted benzaldehydes when oxidized by lead-ruthenium pyrochlore oxide in the presence of sodium hydrochlorite as a co-oxidant at pH 11 under heterogeneous conditions. The reaction of terminal and internal aliphatic alkenes under similar conditions affords no aldehydes.  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-23

京公网安备 11010802026262号