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   254792篇
  免费   3084篇
  国内免费   870篇
电工技术   4919篇
综合类   202篇
化学工业   36607篇
金属工艺   9573篇
机械仪表   7626篇
建筑科学   6132篇
矿业工程   880篇
能源动力   7284篇
轻工业   21310篇
水利工程   2208篇
石油天然气   3230篇
武器工业   15篇
无线电   34444篇
一般工业技术   50402篇
冶金工业   48909篇
原子能技术   5135篇
自动化技术   19870篇
  2022年   1472篇
  2021年   2209篇
  2020年   1570篇
  2019年   1940篇
  2018年   3305篇
  2017年   3330篇
  2016年   3425篇
  2015年   2247篇
  2014年   4006篇
  2013年   11578篇
  2012年   6306篇
  2011年   8685篇
  2010年   6971篇
  2009年   7997篇
  2008年   8492篇
  2007年   8382篇
  2006年   7438篇
  2005年   6577篇
  2004年   6346篇
  2003年   6624篇
  2002年   6097篇
  2001年   6568篇
  2000年   6016篇
  1999年   6444篇
  1998年   16635篇
  1997年   11509篇
  1996年   8888篇
  1995年   6661篇
  1994年   5942篇
  1993年   5878篇
  1992年   4151篇
  1991年   4043篇
  1990年   3882篇
  1989年   3677篇
  1988年   3591篇
  1987年   3036篇
  1986年   2966篇
  1985年   3229篇
  1984年   2942篇
  1983年   2837篇
  1982年   2647篇
  1981年   2553篇
  1980年   2469篇
  1979年   2312篇
  1978年   2121篇
  1977年   2612篇
  1976年   3583篇
  1975年   1768篇
  1974年   1737篇
  1973年   1669篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Eight lactating Holstein dairy cows were fed corn silage-based diets with or without whole cottonseed at 18.5% of the dietary dry matter. At 42 days postpartum, a pulse injection of 100 mg glucose/kg body weight was given intravenously and plasma glucose concentration was monitored for 45 min. At 50 d postpartum, biopsies of adipose tissue and mammary tissue were taken and tissue slices were incubated in vitro with either uniform carbon-14 glucose or 1-carbon-14 palmitate. Basal concentration of plasma glucose was not affected by diet, although apparent distribution volume of glucose did seem to decrease due to feeding whole cottonseed. Feeding whole cottonseed decreased uptake of glucose and palmitate in both adipose tissue and mammary tissue and also decreased oxidation of glucose to carbon dioxide in both tissues. Palmitate oxidation was not affected by diet. Incorporation of carbon-14 from glucose into adipose tissue lipids was decreased in cows fed whole cottonseed. Results indicate that fat supplementation in the form of whole cottonseed may decrease palmitate incorporation and glucose utilization for glycerol and reducing equivalent synthesis in both adipose tissue and mammary tissue of lactating dairy cows.  相似文献   
992.
Most of the UK nuclear power reactors are gas-cooled and graphite moderated. As well as acting as a moderator the graphite also acts as a structural component providing channels for the coolant gas and control rods. For this reason the structural integrity assessments of nuclear graphite components is an essential element of reactor design. In order to perform graphite component stress analysis, the definition of the constitutive equation relating stress and strain for irradiated graphite is required. Apart from the usual elastic and thermal strains, irradiated graphite components are subject to additional strains due to fast neutron irradiation and radiolytic oxidation. In this paper a material model for nuclear graphite is presented along with an example of a stress analysis of a nuclear graphite moderator brick subject to both fast neutron irradiation and radiolytic oxidation.  相似文献   
993.
Passive mode-locking with equidistant ultrashort pulses in the laser cavity due to additional weak modulation of the losses or the refractive index is analyzed. The velocity of the relative pulse motion and the time of establishing the harmonic passive mode-locking mode are analytically estimated. Original Russian Text ¢ A.K. Komarov, 2007, published in Avtometriya, 2007, Vol. 43, No. 3, pp. 100–104.  相似文献   
994.
An expression is derived for the probability of error of an N th-order selection diversity system for the case where the receiver is forced to swell on one channel for several symbols before being allowed to make a decision regarding the best channel. It is found that the time-varying nature of a fading channel causes significant degradation of the probability of error when the dwell time becomes longer than about 10% of the inverse of the fading bandwidth of the channel. The onset of degradation is a function of the signal-to-noise ratio and of the order of diversity. Specific probabilities of error are calculated for differential phase-shift keyed modulation (DPSK). However, the calculations can be done for any other modulation technique  相似文献   
995.
QRS feature extraction using linear prediction   总被引:10,自引:0,他引:10  
This communication proposes a method called linear prediction (a high performant technique in digital speech processing) for analyzing digital ECG signals. There are several significant properties indicating that ECG signals have an important feature in the residual error signal obtained after processing by Durbin's linear prediction algorithm. This communication also indicates that the prediction order need not be more than two for fast arrhythmia detection. The ECG signal classification puts an emphasis on the residual error signal. For each ECG's QRS complex, the feature for recognition is obtained from a nonlinear transformation which transforms every residual error signal to a set of three states pulse-code train relative to the original ECG signal. The pulse-code train has the advantage of easy implementation in digital hardware circuits to achieve automated ECG diagnosis. The algorithm performs very well in feature extraction in arrhythmia detection. Using this method, our studies indicate that the PVC (premature ventricular contraction) detection has at least a 92 percent sensitivity for MIT/BIH arrhythmia database.  相似文献   
996.
997.
The content of tetramethylsuccinonitrile (TMSN), the main decomposition product of 2,2'-azobis-isobutyronitrile, in polyvinyl chloride (PVC) products used for food packaging, were examined as well as food-simulating solvents. The TMSN concentration in 17 PVC products ranged from below the detection limit, 0.05 mg/kg, up to 523 mg/kg. The release of TMSN from two PVC products into five kinds of food-simulating solvents at 60 degrees C for 30 min was observed, except for 1 +/- 1 micrograms/kg of TMSN in n-heptane from a PVC bottle containing 523 +/- 30.4 mg/kg of TMSN. The detection limit of TMSN in the food-simulating solvents was 1 micrograms/kg. When pieces of the bottle were stored in olive oil at 40 degrees C for 120 days, 5 +/- 1 micrograms/kg of TMSN was detected in the oil. The release of TMSN from the pieces of the bottle into olive oil between 80 and 140 degrees C depended on the formula ln y = 0.08786x-5.696, r = 0.9927, where y is the concentration (microgram/kg) of TMSN in olive oil, x is the temperature (degrees C), and r is the correlation coefficient.  相似文献   
998.
999.
1000.
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