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   387篇
  免费   9篇
电工技术   4篇
化学工业   53篇
金属工艺   6篇
机械仪表   15篇
建筑科学   29篇
能源动力   10篇
轻工业   47篇
水利工程   1篇
无线电   23篇
一般工业技术   92篇
冶金工业   73篇
原子能技术   1篇
自动化技术   42篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2020年   5篇
  2019年   4篇
  2018年   6篇
  2017年   4篇
  2016年   6篇
  2015年   8篇
  2014年   12篇
  2013年   27篇
  2012年   24篇
  2011年   27篇
  2010年   26篇
  2009年   16篇
  2008年   20篇
  2007年   13篇
  2006年   17篇
  2005年   14篇
  2004年   14篇
  2003年   12篇
  2002年   7篇
  2001年   5篇
  2000年   6篇
  1999年   8篇
  1998年   22篇
  1997年   9篇
  1996年   11篇
  1995年   9篇
  1994年   5篇
  1993年   4篇
  1992年   2篇
  1991年   5篇
  1990年   4篇
  1989年   1篇
  1988年   2篇
  1986年   1篇
  1983年   2篇
  1981年   3篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1977年   12篇
  1976年   2篇
  1975年   3篇
  1972年   1篇
  1971年   2篇
  1964年   1篇
  1955年   1篇
排序方式: 共有396条查询结果,搜索用时 15 毫秒
1.
B Rune  M Aberg 《Canadian Metallurgical Quarterly》1998,101(2):297-304; discussion 305-6
Bone grafts are used to lengthen the dorsum and elevate the tip of the nose in patients with Binder's syndrome. Disappointing long-term results in some patients generally have been assumed to be a result of resorption and/or displacement of the grafts. Treatment outcome was studied in 11 patients with the use of serial profile roentgenograms. At 40 months, the mean values after surgery were reduction of the initial transplant length by 28 percent and reduction of the transplant angle by 4 degrees. The initial nose length was increased by 1 mm, and nose tip projection was increased by 2 mm. Although the mean changes of nose length and nose tip projection seemed small, treatment outcome varied considerably between patients. In contrast with earlier assumptions, no correlation could be found between the degree of transplant resorption and/or displacement and the effect of surgery on nose length and nose tip projection.  相似文献   
2.
A desired attribute in safety-critical embedded real-time systems is a system time and event synchronization capability on which predictable communication can be established. Focusing on bus-based communication protocols, we present a novel, efficient, and low-cost start-up and restart synchronization approach for TDMA environments. This approach utilizes information about a node's message length that forms a unique sequence to achieve synchronization such that communication overhead can be avoided. We present a fault-tolerant initial synchronization protocol with a bounded start-up time. The protocol avoids start-up collisions by deterministically postponing retries after a collision. We also present a resynchronization strategy that incorporates recovering nodes into synchronization.  相似文献   
3.
Medical students entering the labor market were studied to find out whether the improvement of psychosocial well-being depends on characteristics of their careers. Psychosocial well-being was described on the basis of psychosomatic stress symptoms, psychological distress (General Health Questionnaire), and strain resistance resources (Sense of Coherence). The 3-year follow-up showed that among women the improvement of strain resistance resources was delayed in the group with several entries into work. Among men the findings suggested associations between stress symptoms and career characteristics. Most of the results, however, did not support the hypothesis about the division of the participants into those with a stable career and improving well-being and those with a fragmented career and low well-being. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
4.
5.
The present study investigated if short-term treatment with an L-type Ca2+-channel inhibitor, nimodipine, can stimulate cognitive functioning and cortical electroencephalograph (EEG) arousal, and potentiate the effect of a cholinesterase inhibitor, metrifonate. Pretraining administration of nimodipine (3, 10 and 30 mg/kg, p.o.) had no effect on water maze and passive avoidance behavior of young neurologically intact controls, or water maze and passive avoidance performance failure induced by scopolamine pretreatment (i.p.; 0.4 mg/kg during the water maze and 2.0 mg/kg during the passive avoidance study), medial septal lesioning, or aging. Furthermore, nimodipine (3, 10 and 30 mg/kg, p.o.) had no effect on the improvement by metrifonate (10 mg/kg, p.o.) of the water maze and passive avoidance failure induced by scopolamine pretreatment or medial septal lesioning, nor did it affect the potential of metrifonate (30 mg/kg. p.o.) to improve the water maze or passive avoidance behavior of aged rats. Finally, nimodipine (3, 10 and 30 mg/kg, p.o.) had no effect on spontaneously occurring thalamically generated neocortical high-voltage spindles or spectral EEG activity of young controls, nor did it alleviate the spectral EEG abnormality induced by scopolamine (0.2 mg/kg, i.p.) administration. Also, the combination of nimodipine 3 or 10 mg/kg and a subthreshold dose of metrifonate 10 mg/kg could not suppress high-voltage spindles or scopolamine treatment-induced spectral EEG activity abnormalities. According to the present results, short-term treatment with nimodipine does not stimulate cognitive functions or increase cortical EEG arousal, and does not block or potentiate the propensity of metrifonate to improve cognitive performance of rats.  相似文献   
6.
The resolution in ultrasonic images decreases with depth when using traditional time-gain compensation (TGC) of the received signal. To reduce this effect, both frequency-dependent and depth-dependent compensation is introduced. A time-varying digital filtering method is presented for this purpose, which is based on Wiener filtering. Images obtained from a simulated tissue equivalent are presented and the frequency-compensated images are compared to conventional TGC-compensated images. It is shown that the improvement in resolution using frequency-dependent compensation is considerable when the signal-to-noise ratio in the received signal is high.  相似文献   
7.
A wet air oxidation reaction was carried out in a gas/liquid catalytic membrane reactor of the contactor type. The oxidation of formic acid was used as a model reaction. The mesoporous top-layer of a ceramic tubular membrane was used as catalyst (Pt) support, and was placed at the interface of the gas (air) and liquid (HCOOH solution) phases.

A similar reaction was carried out in a conventional batch reactor, using a steering rate high enough to avoid gas-diffusion limitations, and exactly identical conditions than for the CMR (amount of catalyst, pressure, etc.). At room temperature, the CMR showed an initial activity three to six times higher than the conventional reactor. This activity increase was attributed to an easier oxygen access to the catalytic sites. Nevertheless, the catalytic membrane gradually deactivated after a few hours of operation. Different deactivation mechanisms are presented.  相似文献   

8.
洗油组分的提取、应用及前景   总被引:1,自引:1,他引:1  
杨瑞平  段润娥 《煤化工》2006,34(5):61-64
介绍了目前提取洗油组分的主要工艺过程及洗油中各组分的应用情况,指出我国应加强洗油加工利用的研究和其产品的开发应用:首先必需建设大型洗油加工装置,采用多种加工工艺,提取煤焦油特有的组分;其次提高洗油加工产品的纯度,获得高附加值的产品。  相似文献   
9.
Several novel and some previously known, mostly sugar-based, surfactants have been synthesized and some of their surface properties have been characterized and compared with those of commercial nonylphenol ethoxylates. The surfactant solubility in water, ethanol, and dodecane was studied. The properties of these compounds as emulsification agents in systems composed of the surfactant with water/isopropyl myristate, water/rapeseed oil, and water/dodecane are presented. The aqueous solubility of the surfactants follows the general trend expected from their hydrophilic-lipophilic balance according to Griffin (HLBG), but it is also clear that the nature of the headgroup and the structure of the nonpolar part affect the solubility in a manner not aptured in the standard HLBG concept. An ester or amine group as the connecting unit between the hydrophile and the hydrophobe produces a more water-soluble surfactant than the corresponding amide derivative. Some effective emulsifiers were found. For instance, the surfactants with a dehydroabietic nonpolar group appear to be promosing emulsifiers. Most sugar-based surfactants were able to form macroemulsions of up to around 2 wt/vol% of oil. The stability of many of these amulsions was very high, extending for months.  相似文献   
10.
We have implemented and validated automated protocols for DNA extraction and PCR setup using a Tecan Freedom EVO liquid handler mounted with the Te-MagS magnetic separation device (Tecan, M?nnedorf, Switzerland). The protocols were validated for accredited forensic genetic work according to ISO 17025 using the Qiagen MagAttract DNA Mini M48 kit (Qiagen GmbH, Hilden, Germany) from fresh whole blood and blood from deceased individuals. The workflow was simplified by returning the DNA extracts to the original tubes minimizing the risk of misplacing samples. The tubes that originally contained the samples were washed with MilliQ water before the return of the DNA extracts. The PCR was setup in 96-well microtiter plates. The methods were validated for the kits: AmpF?STR Identifiler, SGM Plus and Yfiler (Applied Biosystems, Foster City, CA), GenePrint FFFL and PowerPlex Y (Promega, Madison, WI). The automated protocols allowed for extraction and addition of PCR master mix of 96 samples within 3.5h. In conclusion, we demonstrated that (1) DNA extraction with magnetic beads and (2) PCR setup for accredited, forensic genetic short tandem repeat typing can be implemented on a simple automated liquid handler leading to the reduction of manual work, and increased quality and throughput.  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