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   780篇
  免费   16篇
  国内免费   2篇
电工技术   6篇
化学工业   117篇
金属工艺   21篇
机械仪表   15篇
建筑科学   31篇
矿业工程   3篇
能源动力   12篇
轻工业   72篇
水利工程   7篇
石油天然气   5篇
无线电   47篇
一般工业技术   131篇
冶金工业   254篇
原子能技术   6篇
自动化技术   71篇
  2022年   11篇
  2021年   17篇
  2020年   5篇
  2019年   6篇
  2018年   8篇
  2017年   8篇
  2016年   6篇
  2015年   14篇
  2014年   14篇
  2013年   38篇
  2012年   23篇
  2011年   31篇
  2010年   32篇
  2009年   34篇
  2008年   38篇
  2007年   42篇
  2006年   36篇
  2005年   23篇
  2004年   22篇
  2003年   27篇
  2002年   19篇
  2001年   20篇
  2000年   10篇
  1999年   19篇
  1998年   56篇
  1997年   22篇
  1996年   15篇
  1995年   10篇
  1994年   14篇
  1993年   22篇
  1992年   10篇
  1991年   11篇
  1990年   15篇
  1989年   8篇
  1988年   6篇
  1987年   7篇
  1985年   8篇
  1984年   9篇
  1983年   7篇
  1982年   8篇
  1981年   6篇
  1980年   7篇
  1979年   7篇
  1978年   4篇
  1977年   4篇
  1976年   6篇
  1974年   4篇
  1973年   4篇
  1972年   5篇
  1971年   3篇
排序方式: 共有798条查询结果,搜索用时 31 毫秒
71.
The need for in situ heat flux measurements in hot structures, used in hypersonic vehicle thermal protection system development, combustion and propulsion research, and fire testing requires that heat flux sensors are characterized over their entire operating temperature range. The in-cavity heat flux sensor calibration technique has been adapted to accommodate elevated sensor temperatures, in an effort to develop a primary calibration scheme for high temperature heat flux sensors using an existing blackbody calibration system. The new scheme has been demonstrated through the calibration of a high temperature, thermopile-type heat flux sensor. The output temperature dependence of the high temperature heat flux sensor (HTHFS) has been successfully characterized over the range of 175–960 °C with acceptable uncertainty limits. The calibrated HTHFS sensitivity agrees well with a theoretical sensitivity model, suggesting that the extended in-cavity calibration technique is a viable choice for primary calibration of heat flux sensors at elevated sensor temperatures.  相似文献   
72.
Through development of a team of Departmental Safety Advisors trained as generalists and supported by subject area experts, the campus community receives efficient, accurate, and personalized help in implementing the safety programs required of the university. The on-call program helps to solve problems and answer questions in a timely manner. The e-mail distribution of on-call information keeps the staff at EH&S informed about what is happening on campus and gives us the opportunity to be proactive problem solvers.Ongoing training of the DSAs, twice-monthly operations meetings, and e-mail keep the lines of communication open between the director and staff and among the staff. The staff feels as though it knows what is going on in the larger scheme of things and that its concerns are respected.The program is continuously improved by evaluating workload, benchmarking with other, similar universities, and feedback from clients.  相似文献   
73.
An experimental study was performed to investigate the effects of added clay particles on the structure and properties of porous, freeze-dried composites produced from silica nanoparticles. The sol–gel transition of the silica suspension arrests the sedimentation of the dense clay platelets to produce a gel, containing large clay particles dispersed throughout. No chemical additives other than sodium chloride were needed to cause the gelation. Dry composites were obtained by subjecting the gelled suspensions to rapid freezing in one of the following ways: submersion in liquid nitrogen or liquid propane, or exposure to low-temperature refrigeration. Frozen samples were then sublimated under vacuum to remove the water. Scanning electron microscope images of the dried composites showed a porous material whose pore sizes decrease with an increasing rate of freezing. The dependence on freeze rate suggests that the porous structure is the result of ice formation. Addition of the clay particles significantly increases the rate of gel formation. Furthermore, the strength of the clay/nanoparticle composites, as measured by normal compression tests, was substantially greater than that of a similar material made with only silica nanoparticles. Finally, BET surface area analysis shows a decreasing surface area with increasing volume fraction of clay at a constant volume fraction of silica.  相似文献   
74.
The dawn of the Atomic Age finds our nation increasingly vulnerable to devastating attack. The risk to both population and nation has long been intolerable. Since such attack would not necessarily be either preventable or totally destructive, all reasonable efforts must be made to reduce this vulnerability while search for a basis for just and enduring peace continues. Reduction of urban vulnerability should especially concern planners. Working together with others, they can and should contribute to the development of policy and the carrying out of measures for reduction of vulnerability coordinated with improvement of livability on broad regional, state, and national bases.  相似文献   
75.
76.
Diets high in omega-6 polyunsaturated fatty acids (n-6) are associated with increased prostaglandin F (PGF) synthesis in cattle, however, the specific effects on the potential prostaglandin response to an oxytocin challenge in sheep have not been reported. The aim of the current study was to determine whether oxytocin-stimulated PGF was significantly increased when ewes were fed a diet high in n-6 compared with a control diet low in n-6. Merino x Border Leicester ewes (n = 30) received one of two dietary treatments, either high in n-6 (70 % oat grain) or low in n-6 (control diet, 100 % cereal/legume silage). Ewes consumed the diets for 44 days prior to two consecutive oxytocin challenges. Plasma n-6 and PGF metabolite (PGFM) concentrations following oxytocin challenge were greater (P < 0.05) when ewes were fed a diet high in n-6 compared with the control diet. A higher availability of n-6 may have lead to an increased in vivo synthesis of PGF, however, further research is required to determine the exact mechanisms involved.  相似文献   
77.
The Rey-Osterrieth Complex Figure (ROCF) is commonly used to assess visuospatial skills, visuoconstruction, visual memory, and executive functioning. Two different methods are traditionally used to record the order in which the figure is drawn: the flowchart method and the pen-switching method. Although it has been suggested that pen switching may interfere with performance, to date no research has been conducted to assess whether ROCF performance significantly differs due to administration method. As part of routine neuropsychological evaluation, 100 inpatients and outpatients were randomly assigned to either method. Using the Boston Qualitative Scoring System and the traditional 36-point scoring method, the authors unexpectedly found that the pen-switching group generally performed better than the flowchart group, and productions drawn with pen switching were also significantly faster to score. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
BACKGROUND/AIMS: Liver failure in infancy can result from several disorders of the mitochondrial respiratory chain. In some patients, levels of mitochondrial DNA are markedly reduced, a phenomenon referred to as mitochondrial DNA depletion. To facilitate diagnosis of this condition, we have reviewed the clinical and pathological features in five patients with mitochondrial DNA depletion. METHODS: Cases were identified by preparing Southern blots of DNA from muscle and liver, hybridising with appropriate probes and quantifying mitochondrial DNA relative to nuclear DNA. RESULTS: All our patients with mitochondrial DNA depletion died of liver failure. Other problems included hypotonia, hypoglycaemia, neurological abnormalities (including Leigh syndrome) and cataracts. Liver histology showed geographic areas of fatty change, bile duct proliferation, collapse of liver architecture and fibrosis; some cells showed decreased cytochrome oxidase activity. Muscle from three patients showed mitochondrial proliferation, with loss of cytochrome oxidase activity in some fibres but not in others; in these cases, muscle mitochondrial DNA levels were less than 5% of the median control value. The remaining two patients (from a single pedigree) had normal muscle histology and histochemistry associated with less severe depletion of mitochondrial DNA in muscle. CONCLUSIONS: Liver failure is common in patients with mitochondrial DNA depletion. Associated clinical features often include neuromuscular disease. Liver and muscle histology can be helpful in making the diagnosis. Mitochondrial DNA levels should be measured whenever liver failure is thought to have resulted from respiratory chain disease.  相似文献   
79.
Determination of turbidity is a common component of water-quality assessments. In regions where there are a lot of inland waters such as dams, sampling even a small proportion of those dams for monitoring and assessing water quality is cost prohibitive. Satellite remote sensing has the potential to be a powerful tool for assessing water quality over large spatial scales. The overall objective of this study was to examine whether Landsat-5 TM (Thematic Mapper) and Landsat-7 ETM+ (Enhanced Thematic Mapper) could be used to measure turbidity across theKourris Dam, which is the biggest dam in Cyprus. This paper presents the results obtained by applying the linear regression analysis in order to examine the relationship between the turbidity measurements measured in-situ during the satellite overpass against at-satellite atmospheric corrected reflectance values. It has been found that the reflectance, after atmospheric correction, at LandsatTMBands 1 and 3 is strongly related with turbidity levels after linear regression analysis. The most significant correlation was occurred when reflectance in TM band 3 and logarithmic reflectance in TM band 3 were correlated with turbidity measurements. Indeed, the correlation coefficient (R) when atmospheric corrected reflectance (ρ) in the LandsatTMband 3 were correlated against turbidity, before atmospheric correction was R = 0.38 and after atmospheric correction was R = 1; and when atmospheric corrected logarithmic reflectance (Log ρ) in the Landsat TM band 3 were correlated against turbidity, before atmospheric correction was R = 0.46 and after atmospheric correction was R = 1.  相似文献   
80.
Two studies examined the association between newscasters' facial expressions and the voting behavior of viewers. In Exp I, with 45 undergraduates, the facial expressions exhibited by network newscasters while referring to the 1984 presidential candidates prior to the election were investigated. Results indicate that 1 of the 3 newscasters exhibited significantly more positive facial expressions when referring to Reagan than when referring to Mondale. In Exp II, a telephone survey of approximately 200 individuals was conducted to determine whether voting behavior was associated with the nightly news program watched. It was found that voters who regularly watched the newscaster who exhibited the biased facial expressions were significantly more likely to vote for the candidate that the newscaster had smiled upon. Three explanations for the results are discussed: (1) Viewing the newscasters' biased facial expressions caused the viewers' voting preferences; (2) the viewers' voting preferences determined their viewing of biased newscasters' facial expressions; or (3) some other variable accounted for the findings. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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