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   252383篇
  免费   4704篇
  国内免费   685篇
电工技术   3852篇
综合类   195篇
化学工业   40294篇
金属工艺   9051篇
机械仪表   7088篇
建筑科学   6423篇
矿业工程   1422篇
能源动力   6469篇
轻工业   26021篇
水利工程   2793篇
石油天然气   4254篇
武器工业   15篇
无线电   25119篇
一般工业技术   48188篇
冶金工业   48218篇
原子能技术   5346篇
自动化技术   23024篇
  2022年   1813篇
  2021年   2969篇
  2020年   2200篇
  2019年   2820篇
  2018年   4408篇
  2017年   4435篇
  2016年   4717篇
  2015年   3306篇
  2014年   4995篇
  2013年   12791篇
  2012年   8013篇
  2011年   10096篇
  2010年   8041篇
  2009年   8695篇
  2008年   8633篇
  2007年   8439篇
  2006年   7031篇
  2005年   6499篇
  2004年   6179篇
  2003年   5941篇
  2002年   5508篇
  2001年   5346篇
  2000年   5258篇
  1999年   5468篇
  1998年   14740篇
  1997年   10380篇
  1996年   7942篇
  1995年   5544篇
  1994年   4992篇
  1993年   4896篇
  1992年   3514篇
  1991年   3374篇
  1990年   3109篇
  1989年   3209篇
  1988年   3068篇
  1987年   2615篇
  1986年   2496篇
  1985年   2944篇
  1984年   2683篇
  1983年   2486篇
  1982年   2264篇
  1981年   2403篇
  1980年   2231篇
  1979年   2232篇
  1978年   2222篇
  1977年   2728篇
  1976年   3965篇
  1975年   1910篇
  1974年   1817篇
  1973年   1860篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Photocatalytic ozonation (1O3 + VUV + TiO2), ozonation (O3), catalytic ozonation (O3 + TiO2), ozone photolysis (O3 + VUV), photocatalysis (TiO2 + VUV) and photolysis (VUV) have been compared in terms of formation of intermediates, extent of, mineralization (TOC, COD, chloride, nitrate) and kinetics in the aqueous treatment of three phenols (phenol, p‐chlorophenol and p‐nitrophenol). In all cases, photocatalytic ozonation led to lower degradation times for chemical oxygen demand and total organic carbon removal. Intermediates formed were similar in the different oxidation systems with some exceptions. They can be classified into three different types: polyphenols (resorcinol, catechol, hydroquinone), unsaturated carboxylic acids (maleic and fumaric acids) and saturated carboxylic acids (glyoxylic, formic and oxalic acids). First order kinetic equations have been checked for the oxidation processes studied in the case of the parent compound. Rate constants of these systems have also been calculated. Copyright © 2005 Society of Chemical Industry  相似文献   
102.
103.
104.
105.
Neural networks and blood cell identification   总被引:1,自引:0,他引:1  
The objective of this project is to propose a method of identifying cells found in human blood and to classify them based upon their morphological features using neural networks. The project focuses on three major blood cell types, namely, erythrocytes, leukocytes and platelets. The data are collected using peripheral blood smears from clinical patients. The image acquisition requires 100x magnification on all the blood smears, the preprocessing involves the use of median and edge enhance filters; the feature extraction is done by performing the wavelet transform on the images. Finally classification of the blood cell types is done using ALOPEX and Back Propagation trained neural networks. The efficacy of both networks is then compared by comparing their outputs and number of iterations required to reach the final result.  相似文献   
106.
Penetrating injuries of the eye are an important cause of unilateral visual loss. We studied a series of 82 cases of penetrating injuries treated here from 1987 through 1993. The injuries were caused by sharp objects in 66% and blunt trauma in 6%. The prognosis after a penetrating injury is greatly influenced by the nature of the injury and the extent of the initial drainage. Among factors associated with an unfavorable visual outcome were diminished preoperative visual acuity and scleral wounds with dense vitreous hemorrhage.  相似文献   
107.
A wideband wattmeter for measuring active power over a frequency range of dc to 500 kHz is described. The wattmeter is based on the three-voltmeter method in which three rms voltage measurements are used to calculate power. The wattmeter active power uncertainty is estimated to be within 0.03% from dc to 20 kHz and within 1.5% to 500 kHz  相似文献   
108.
109.
Recent studies have identified molecules that interact with integrins and appear to participate in the signaling pathways that regulate integrin adhesiveness. Clues provided by studies of these molecules point to the integration by integrins of signal transduction pathways implicated in cell division and activation.  相似文献   
110.
The cytosolic chaperonin containing TCP-1 (CCT) is known to keep fold cytoskeletal proteins and is involved in the proper organization of the cytoskeleton. These studies are based on the assumption that growth responses linked to structural rearrangement of the plant cytoskeleton include the action of CCT and the need for newly synthesized tubulin. The presence of the alpha- and epsilon-subunits of CCT was investigated in soluble fractions of protein extracts from maize mesocotyls and coleoptiles at distinct growth stages. The CCT-subunits, tubulins and actin decreased in the coleoptile in response to far-red light. In addition, independent from light treatment, the amount of CCT epsilon abundance declined with age in coleoptiles and mesocotyls between 2 and 4.5 days after sowing. In contrast to CCT epsilon, no significant light regulation of CCT alpha was found in the mesocotyl. In two day old, light-grown rapidly elongating coleoptiles part of the CCT alpha subunit and the bulk of actin and tubulin was found shifted into fractions of high molecular weight complexes when compared to slowly elongating, dark grown coleoptiles. In 4.5 day old, etiolated and elongating coleoptiles, part of both CCT-subunits and cytoskeleton proteins were found in fractions of high molecular weight. A complete disappearance of these polypeptides was observed in old far-red irradiated growth-arrested coleoptiles. CCT epsilon was found to be colocalized to microtubular structures and to the nucleus. We conclude from our data that abundance of CCT-subunits in soluble extracts is dependent on age and light treatment, but independent from the growth stage of mesocotyl and coleoptile.  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