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   92篇
  免费   0篇
电工技术   1篇
化学工业   12篇
金属工艺   1篇
机械仪表   3篇
建筑科学   2篇
轻工业   5篇
无线电   13篇
一般工业技术   33篇
冶金工业   15篇
自动化技术   7篇
  2023年   2篇
  2022年   1篇
  2021年   1篇
  2020年   1篇
  2019年   1篇
  2015年   2篇
  2013年   1篇
  2012年   6篇
  2011年   10篇
  2010年   2篇
  2008年   7篇
  2007年   7篇
  2006年   4篇
  2005年   7篇
  2004年   3篇
  2003年   2篇
  2002年   3篇
  2001年   3篇
  2000年   5篇
  1999年   1篇
  1998年   5篇
  1997年   2篇
  1996年   2篇
  1994年   1篇
  1993年   2篇
  1992年   4篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
  1982年   3篇
  1979年   1篇
排序方式: 共有92条查询结果,搜索用时 15 毫秒
1.
The changes in lipoprotein(a) concentration that occur with age as a result of its association with an increased risk of coronary artery disease were investigated. Lipoprotein(a) concentrations were measured in serum samples from healthy volunteers, individuals with premature coronary artery disease, individuals with hyperlipidaemia but without evidence of premature coronary artery disease, and also in elderly men and women who had hyperlipidaemia. Concentrations in individuals with premature coronary artery disease were the same as those of the healthy volunteers, while in both these groups they were lower than those found in hyperlipidaemic elderly men and women, and those found in hyperlipidaemic women aged 36-68 years. No association between raised lipoprotein(a) concentration and mortality as a result of premature coronary artery disease was demonstrated. Raised lipoprotein(a) levels found in the hyperlipidaemic individuals also suggested that it may not be an independent risk factor.  相似文献   
2.
3.
The redox chemistry of thallium clusters in aqueous solution has been investigated by pulse radiolysis and γ-radiolysis. Using Ru(bpy)32+ as a redox indicator, it is shown that the redox potential of the Tl42+/+ couple is more positive than −1.27 V NHE, and that the Tl+/Tl2+ couple's redox potential is more negative than −1.27 V NHE. Ru(bpy)3+ reduces Tl42+ with a second-order rate constant of 6±2 × 108 M−1s−1. Metallic particles of thallium are predicted to have a surface plasmon absorption band at 205 nm in water. The reduced Tl content in a sol can be measured by air-free titration with CCl4 or methylviologen.  相似文献   
4.
Two new electrophilic monomers, 7,8-di(alkoxycarbonyl)-7,8-dicyanoquinodimethanes, were prepared. These quinodimethanes exhibit moderate electron-acceptor abilities and are highly reactive toward spontaneous homopolymerization in solution as well as in the solid state. Quinodimethane homopolymers were also obtained from heterogeneous spontaneous solution polymerization in the presence of styrene, p-methoxystyrene and isobutyl vinyl ether.  相似文献   
5.
6.
A simple procedure for creating titania sol–gel‐based semiconductor thin films is described. Gold nanoparticles are doped homogeneously into the precursor mixture and the particles are homogeneously distributed in the resultant films when prepared using spin‐coating. The effects of particle loading and annealing temperature on the optical properties of the resultant films are characterized. Ellipsometry, X‐ray diffraction, atomic force microscopy, and surface plasmon spectroscopy are used to monitor the crystallization and porosity changes during film synthesis.  相似文献   
7.
This study examined the relation between depression diagnoses and outcomes in 132 cocaine-dependent patients who were randomized to relapse prevention (RP) or standard 12-step focused group continuing rare and followed for 2 years. Depressed patients attended more treatment sessions and had more cocaine-free urines during treatment than participants without depression, but they drank alcohol more frequently before treatment and during the 18-month posttreatment follow-up. Cocaine outcomes in depressed patients deteriorated to a greater degree after treatment than did cocaine outcomes in patients without depression, particularly in patients in RP who had a current depressive disorder at baseline. The best alcohol outcomes were obtained in nondepressed patients who received RIP. The results suggest that extended continuing care treatment may be warranted for cocaine-dependent patients with co-occurring depressive disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
8.
9.
Continuous wave Doppler methods have been widely used clinically for evaluating the severity of aortic regurgitation; however, there have been no studies comparing these continuous wave Doppler methods with a strictly quantifiable reference for regurgitant severity. The purpose of this study was to test the applicability of continuous wave Doppler methods (deceleration slope and pressure half-time) for evaluation of chronic aortic regurgitation in an animal model. Eight sheep were studied 8 to 20 weeks after surgery to create chronic aortic regurgitation. Twenty-nine hemodynamically different states were obtained pharmacologically. A Vingmed 775 system was used for recording continuous wave Doppler traces with a 5 MHz annular array transducer directly placed on the heart near the apex. The aortic regurgitation was quantified as peak and mean regurgitant flow rates, regurgitant stroke volumes and regurgitant fractions determined with pulmonary and aortic electromagnetic flow probes and meters balanced against each other. Peak regurgitant flow rates varied from 1.8 to 13.6 L/min (6.3 +/- 3.2 L/min) (mean +/- SD), mean regurgitant flow rates varied from 0.7 to 4.9 L/min (2.7 +/- 1.3 L/min), regurgitant stroke volume varied from 7.0 to 48.0 ml/beat (26.9 +/- 12.2 ml/beat), and regurgitant fraction varied from 23% to 78% (53% +/- 16%). Only marginal correlations were obtained between reference indexes and continuous wave Doppler deceleration slope and pressure half-time (r = 0.55 to 0.74). A deceleration slope greater than 3 m/sec2 and pressure half-time less than 400 msec did, however, provide 100% specificity for detecting severe AR (regurgitant fraction > 50%). Our study shows that the continuous wave Doppler deceleration slope and pressure half-time methods have limited use for quantifying aortic regurgitation.  相似文献   
10.
A fully integrated transceiver suitable for low-data-rate wireless telemetry and sensor networks operating in the license-free ISM frequency bands at 433, 868, or 915 MHz implemented in 0.25-/spl mu/m CMOS is presented. G/FSK, ASK, and OOK modulation formats are supported at data rates from 0.3 to 200 kb/s. The transceiver's analog building blocks include a low-noise amplifier, mixer, channel filter, received signal-strength indication, frequency synthesizer, voltage-controlled oscillator, and power amplifier. FSK demodulation is implemented using a novel digital complex-frequency correlator that operates over a wide modulation-index range and approximates matched filter detection performance. Automatic gain control, automatic frequency control, and symbol timing recovery loops are included on chip. Operating in the 915-MHz band in FSK mode at 9.6 kb/s, the receiver consumes 19.7 mA from a 3-V supply and achieves a sensitivity of -112.8dBm at 0.1% BER. The transmitter consumes 28.5 mA for an output power of 10 dBm and delivers up to 14 dBm.  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