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   2984篇
  免费   109篇
  国内免费   19篇
电工技术   142篇
综合类   10篇
化学工业   732篇
金属工艺   80篇
机械仪表   100篇
建筑科学   102篇
矿业工程   8篇
能源动力   108篇
轻工业   231篇
水利工程   17篇
石油天然气   15篇
无线电   261篇
一般工业技术   571篇
冶金工业   446篇
原子能技术   104篇
自动化技术   185篇
  2024年   7篇
  2023年   33篇
  2022年   54篇
  2021年   88篇
  2020年   41篇
  2019年   38篇
  2018年   46篇
  2017年   42篇
  2016年   66篇
  2015年   45篇
  2014年   60篇
  2013年   170篇
  2012年   110篇
  2011年   174篇
  2010年   118篇
  2009年   128篇
  2008年   118篇
  2007年   116篇
  2006年   106篇
  2005年   96篇
  2004年   68篇
  2003年   90篇
  2002年   91篇
  2001年   70篇
  2000年   72篇
  1999年   65篇
  1998年   200篇
  1997年   115篇
  1996年   84篇
  1995年   61篇
  1994年   54篇
  1993年   54篇
  1992年   33篇
  1991年   28篇
  1990年   23篇
  1989年   28篇
  1988年   27篇
  1987年   21篇
  1986年   29篇
  1985年   31篇
  1984年   22篇
  1983年   22篇
  1982年   19篇
  1981年   22篇
  1980年   19篇
  1979年   14篇
  1978年   11篇
  1977年   12篇
  1976年   36篇
  1975年   8篇
排序方式: 共有3112条查询结果,搜索用时 484 毫秒
221.
Hybrid bubble memory devices have been proposed and operated with the memory density of 4 Mbit/cm2. In the hybrid bubble memory devices, minor loops are composed of ion-implanted tracks with 4-µm period, and major lines and functional parts including block-replicate and swap gates are composed of Permalloy tracks with a longer period of 12 µm. Passive junctions between ion-implanted and Permalloy tracks have been developed, introducing the tapered ion-implantation technique. Improving the characteristics of the functional parts composed of Permalloy tracks, the hybrid bubble memory devices with block-replicate and swap gates have been operated, and the feasibility of the devices has been confirmed. In addition, the possibility of higher memory density has been shown.  相似文献   
222.
Recently, there has been an increase in concern about the global environment. Interest is growing in developing an energy network by which new energy systems such as photovoltaic and fuel cells generate power locally and electrical power and heat are controlled with a communication network. We developed the power generation forecast method for photovoltaic power systems in an energy network. The method makes use of weather information and regression analysis. We carried out forecasting power output of the photovoltaic power system installed in Expo 2005, Aichi Japan. As a result of comparing measurements with prediction values, the average prediction error per day was about 26% of the measured power. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(4): 16–23, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20755  相似文献   
223.
The longstanding question as to whether carbon nanotubes are intrinsically toxic hinders their widespread industrial application. Here, we clarify the effect of impurities within such tubes through systemic studies of immunological responses in mice by monitoring and examining changes in peripheral T-cell subset and peripheral cytokine levels and histology. Contaminated and clean tubes were subcutaneously implanted in mice. The implanted tubes with impurities clearly induced immunological toxicity and localized alopecia, whereas extremely pure implanted tubes showed good biocompatibility. Our studies suggest that such high-temperature thermal treatment is an effective way to improve the biocompatibility of carbon nanotube.  相似文献   
224.
Synchrotron X-ray radiography at 125 frames per second was used to study deformation mechanisms in semi-solid Fe-C alloys at high solid fraction and shear strain rates of 10?1/s. An image correlation approach was also used to quantify the shear strain fields and study shear-induced dilation and the origin of shear cracking. It was shown that, at high solid fraction (90 to 93 pct solid), rearrangement including rotation and translation of solid particles became restricted and shear strain localized into narrow liquid-filled channels/fissures. Shear cracking was shown to originate from inadequate liquid flow into the expanding spaces between solid particles caused by shear-induced dilation. At lower solid fraction (~85 pct solid), solid particles rearranged with a significantly higher component of rotation leading to more shear-induced dilation and a wider shear band.  相似文献   
225.
226.
When two targets (T1 and T2) are embedded in rapid serial visual presentation (RSVP), T2 is often missed (attentional blink, AB) if T2 follows T1 by less than 500 ms. Some have proposed that inhibition of a distractor following T1 contributes to the AB, but no direct evidence supports this proposal. This study examined distractor inhibition by assessing a distractor devaluation effect where inhibited items were evaluated less positively than controls. Experiments 1 and 2 showed that a distractor presented just after T1 was evaluated less favorably when T2 was misidentified, independently of stimulus characteristics. Experiment 3 produced distractor devaluation in T2 incorrect trials when the evaluated distractor was the second item after T1. In contrast, a distractor presented before T1 was not devaluated (Experiment 4). Experiment 5 demonstrated that participants could not recognize presented distractors after an RSVP task, rejecting the possibility that memorized distractors were devalued. Results show a relationship between the devaluation of distractors following T1 and the AB, providing the first direct evidence of the distractor inhibition during the AB. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
227.
This paper presents a hysteresis model of soil water retention curves based on bounding surface concept. In the bounding surface concept, the plastic modulus is defined as a function of the distance between a current stress point and the conjugated stress point on the bounding surface. We adopt the similar idea that the slopes c (=??Sr/?s) of soil water retention curves are defined as a function of the normalized distance between a current point and the conjugated points on main curves (main drying and wetting curves). The modeling of main curves was conducted by Tangential model proposed by the author. Tangential model insures the continuity of slopes of soil water retention curves. The model may well trace the soil water retention curves as if pore water pressures are both positive and negative. The model needs not to identify the parameters. Only three points are selected and the values of degree of saturation Sr, suction s and slope c at the points are input. Soil water retention curves for three samples with cycles of drying and wetting were simulated using the model. The simulation results showed good agreements with the experimental ones.  相似文献   
228.
Acidic hydrothermal degradation of glucose was examined in the presence of HCl, H2SO4, and H3PO4 with pH varying from 1.5 to 2.5 and reaction time varying from 1 to 10 min at 523 K, to investigate the effect of different acid catalysts and acid concentration on the production of 5-hydroxymethyl-2-furaldehyde (HMF) and levulinic acid from glucose. At lower acidities of pH 2.5, a considerably higher amount of HMF was produced. The increase in acid concentration accelerated the conversion of HMF to levulinic acid. The order for the production of HMF using the three acids is in the sequence of H3PO4 > H2SO4 > HCl. On the contrary, the order for production of levulinic acid follows HCl > H2SO4 > H3PO4. In the experimental conditions used in this study, the highest yield of levulinic acid is about 55%, which was obtained at pH 1.5 for 5 min in the case of HCl as an acid catalyst, and the total highest yields of HMF and levulinic acid are about 50%, which occurred at pH 2.0 for 5 min in the case of H3PO4 as an acid catalyst.  相似文献   
229.
230.
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