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   558篇
  免费   43篇
  国内免费   1篇
电工技术   7篇
化学工业   148篇
金属工艺   4篇
建筑科学   31篇
矿业工程   1篇
能源动力   15篇
轻工业   102篇
水利工程   7篇
石油天然气   3篇
无线电   45篇
一般工业技术   84篇
冶金工业   86篇
原子能技术   6篇
自动化技术   63篇
  2024年   1篇
  2023年   3篇
  2022年   18篇
  2021年   28篇
  2020年   10篇
  2019年   9篇
  2018年   17篇
  2017年   17篇
  2016年   19篇
  2015年   21篇
  2014年   27篇
  2013年   34篇
  2012年   36篇
  2011年   37篇
  2010年   35篇
  2009年   28篇
  2008年   42篇
  2007年   20篇
  2006年   24篇
  2005年   22篇
  2004年   17篇
  2003年   16篇
  2002年   14篇
  2001年   12篇
  2000年   5篇
  1999年   7篇
  1998年   12篇
  1997年   16篇
  1996年   6篇
  1995年   3篇
  1994年   4篇
  1993年   6篇
  1992年   5篇
  1991年   2篇
  1990年   4篇
  1989年   2篇
  1988年   1篇
  1986年   1篇
  1985年   3篇
  1984年   2篇
  1982年   1篇
  1981年   4篇
  1978年   2篇
  1977年   2篇
  1976年   4篇
  1969年   1篇
  1964年   1篇
  1947年   1篇
排序方式: 共有602条查询结果,搜索用时 140 毫秒
31.
The high comorbidity of depression and anxiety is well established empirically but not well understood conceptually, in terms of either psychological or biological mechanisms. A neuropsychological model of regional brain activity in emotion provides contrasting hypotheses for depression and anxiety, with depression associated with a relative decrease and anxiety with a relative increase in right-posterior activity. These hypotheses received support in a comparison of individuals diagnosed with depression and community controls, and also in a separate study of nonpatients administered a measure of perceptual asymmetry. Hierarchical regressions revealed that depression and anxiety were uniquely and jointly associated with perceptual asymmetry. In light of consistent empirical support for the model, implications for conceptualizations of the comorbidity of depression and anxiety are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
32.
Compared the processing and retrieval of attribution-relevant information when the attributional inference is easy or difficult to make. Ss attributed behavioral events to the person or to the situation, based on several items of context information. Each context sentence implied either the person or the entity as causal agent. When the attributional inference was difficult to make (an equal number of context sentences implied actor and entity as the causal agent), Ss recalled more of the behavioral events, recalled more context sentences, and were less confident in their attributions than when the attributional inference was easy to make (most context sentences implied the same causal agent). Ss also recalled context information that was implicationally incongruent with the majority of the other context sentences with a higher probability than when that same information was implicationally congruent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
33.
34.
A modification of Association of Official Analytical Chemists (AOAC) method 983.23 for the quantitative determination of total lipid in food composites was evaluated for the measurement of total fat. The procedure is based on the Bligh and Dyer chloroform/methanol total lipid extraction. Relative to AOAC 983.23, the proposed method is less labor-intensive and is applicable to batch analysis of a larger number of samples, thus reducing the cost of analysis and increasing sample throughput. Total lipid values from the proposed method are comparable to those from AOAC 983.23 and slightly higher than total fat determined by acid hydrolysis (AOAC 954.02, 945.44, or 922.06). Recoveries of standard additions of different food-grade oils from a mixed food composite were essentially quantitative, ranging from 96 to 101%. Total lipid measured in Total Diet Standard Reference Material 1548 (SRM 1548, National Institute of Standards and Technology) was 101% of the certified mean total fat content and within the certified range. The method is to be suitable for analysis of food composites with between 0.15 and 1.5 g total fat (3 to 30% by weight). More than 600 samples of a variety of total diet composites were collected and assayed as diet quality control samples for two National Heart, Lung and Blood Institute-sponsored multicenter clinical feeding trials: DELTA (Dietary Effects on Lipoproteins and Thrombogenic Activity) and DASH (Dietary Approaches to Stop Hypertension). The mean coefficient of variation was 1.2% for duplicate assays of these samples over the course of two years and multiple analysts. In addition, total lipid values for more than 200 samples of a diet composite quality control material, used in this laboratory over a two-year period, had a 3.99% coefficient of variation. Although the accuracy of all gravimetric total fat methods with respect to the U.S. Food and Drug Administration’s Nutritional Labeling and Education Act (NLEA) definition of total fat as the sum of triglycerides remains to be determined, the reported modification of AOAC 983.23 yields a total fat content of acceptable accuracy relative to other gravimetric methods, and with proper quality control the method has excellent precision.  相似文献   
35.
测试、校准、普通系统操作等模拟应用经常需要具有准确的振幅和频率、THDf总谐波失真)很低的正弦波形。一些应用要求此类波形发生器能用外部时序信号使其输出准确同步。简单的正弦波发生器能提供多个性能级别,但保持低THD和恒定振幅是个问题,特别是如果输出和同步信号必须在扩展的频率范围内保持锁定的话。  相似文献   
36.
Thin PDMS films with complex microstructures are used in the manufacturing of dielectric electro active polymer (DEAP) actuators, sensors and generators, to protect the metal electrode from large strains and to assure controlled actuation. The current manufacturing process at Danfoss Polypower A/S produces films with a one-sided microstructured surface only. It would be advantageous to produce a film with both surfaces microstructured, as this increases the film’s performance efficiency. The new technique introduced herein produces bilaterally microstructured film by combining an embossing method with the existing manufacturing process. In employing the new technique, films with microstructures on both surfaces are successfully made with two different liquid silicone rubber (LSR) formulations: 1) pure XLR630 and 2) XLR630 with titanium dioxide (TiO2). The LSR films (~70 µm) are cast on a carrier web substrate using a coating blade. The carrier web, which has a sinusoidal corrugation with wave height of 7 µm and a wave period of 7 µm on its surface, imparts corrugations to the bottom surface of the film. The elastomer film on the carrier web is preheated to the gel point, where the elastomer film can retain an imprint made on it. The preheated film at gel point is embossed between the rolls of a gravure lab coater, which corrugates the top surface of the film. The films are then heated, in order to cure completely. For the LSR systems used in this process, the optimum conditions for preheating are 110°C for 4–7 s, while for embossing the temperature is 110°C with 25 psi pressure between the rolls at a speed of 1.4 rpm. Scanning electron microscope (SEM) images confirm the formation of microstructures on both the surfaces of the film.  相似文献   
37.
现代建筑派大师之一的密斯·凡德罗有句名言:"Less is more","少即是多"衍生出的简约主义,倡导"简约而不简单"的生活哲学.它是被建筑师、画家、音乐家、作家不停探索的美学定义,一种文化倾向,一种时尚潮流.  相似文献   
38.
据iSuppli公司,在第二季度10大智能手机厂商中,增长最快的厂商大多采用了Android操作系统,这表明谷歌的Android系统势头增强. Droid手机专业厂商HTC,第二季度智能手机出货量比第一季度大增63.1%,增长率居业内之首.  相似文献   
39.

Purpose

To investigate the effects of short-term orthokeratology (OK) on accommodation and binocular visual function in young adults.

Methods

Twenty-four myopes (18 to 38 years) were fitted with OK lenses in both eyes. Best corrected distance visual acuity (VA), subjective and objective refractions, corneal topography and a series of binocular vision tests were measured at baseline (BL) before lens wear and then repeated after 28 nights of OK. Data from 15 subjects who demonstrated successful OK lens fit are reported.

Results

Corneal flattening and hyperopic shifts in spherical equivalent refractive error (all p?<?0.001) after 28 nights of OK indicated myopic correction. Improvement in best corrected distance VA was measured after OK (right eye p?=?0.021; left eye p?=?0.014). Although there was no significant change in mean distance and near phorias and stereoacuity scores after OK compared to BL, there was a significant reduction in standard deviation (SD) and range of data (distance p?=?0.01; near p?=?0.02; stereoacuity p?<?0.001). While there appeared to be an improvement in distance accommodative facility after OK, this failed to reach statistical significance (p?=?0.053). Furthermore, there was no change in AC/A gradients with ±1 D and ±2 D lenses after OK compared to BL.

Conclusions

Binocular vision remained unchanged after OK, although variability of phoria and stereoacuity measures reduced. This suggests that OK improves or maintains accommodative and binocular vision function in young adult myopes who achieve good vision with OK. Myopes with phorias outside normal ranges and/or poor distance accommodative facility may benefit most with OK, in binocular and accommodative function.  相似文献   
40.
A photovoltaic panel with a heat extraction system is studied. The solution we suggest consists in superimposing a water layer on the PV panel: the water layer absorbs the infrared radiation leaving the visible part almost unaffected. This allows a good PV efficiency and heat production. This particular setup is called Thermal Electric Solar Panel Integration (TESPI) and it is discussed in detail both for the electric and the thermal part. The engineering problems are briefly analyzed and results of an experimental campaign are given. A definition of the global thermal-electric efficiency is given.  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