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   4652篇
  免费   117篇
  国内免费   4篇
电工技术   38篇
综合类   1篇
化学工业   1006篇
金属工艺   56篇
机械仪表   80篇
建筑科学   242篇
矿业工程   21篇
能源动力   75篇
轻工业   438篇
水利工程   35篇
石油天然气   20篇
无线电   220篇
一般工业技术   854篇
冶金工业   1092篇
原子能技术   33篇
自动化技术   562篇
  2022年   26篇
  2021年   41篇
  2020年   46篇
  2019年   46篇
  2018年   58篇
  2017年   42篇
  2016年   72篇
  2015年   67篇
  2014年   127篇
  2013年   274篇
  2012年   188篇
  2011年   250篇
  2010年   169篇
  2009年   183篇
  2008年   236篇
  2007年   200篇
  2006年   212篇
  2005年   189篇
  2004年   147篇
  2003年   138篇
  2002年   127篇
  2001年   84篇
  2000年   100篇
  1999年   74篇
  1998年   78篇
  1997年   96篇
  1996年   88篇
  1995年   69篇
  1994年   77篇
  1993年   83篇
  1992年   81篇
  1991年   53篇
  1990年   78篇
  1989年   73篇
  1988年   55篇
  1987年   76篇
  1986年   70篇
  1985年   78篇
  1984年   76篇
  1983年   55篇
  1982年   58篇
  1981年   61篇
  1980年   35篇
  1979年   51篇
  1978年   48篇
  1977年   37篇
  1976年   32篇
  1975年   32篇
  1974年   28篇
  1973年   27篇
排序方式: 共有4773条查询结果,搜索用时 15 毫秒
991.
The qualifications of test purchasers have been a concern of the American Psychological Association since 1950, when ethical standards for test distribution, on the basis of a 3-level classification of tests, were developed. The standards relied on professional credentials and on occupational titles to screen test purchasers. In response to widespread recognition that credentials and titles were inadequate to screen test purchasers, the Test User Qualifications Working Group used 2 job analysis methods to determine test user competencies. This article describes the results of that research that can be applied to improving testing practices, including (a) 86 test user competencies and 7 factors accounting for much test misuse, (b) a test classification system based on critical incidents of test misuse, and (c) empirically based test purchaser qualification forms. These products are designed to help achieve responsible test use. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
992.
993.
Abstract: During the last decade, cumulative trauma disorders have become a major concern both to occupational health and safety professionals and manufacturing industries. This paper will present the development of a knowledge-based system for predicting the potential of developing strain injuries among employees exposed to repetitive and forceful activities. This potential is identified through the use of an expert system incorporating a fuzzy set algorithm. Recommendations for the prevention of the resulting CTDs are then provided by the system. The system executes on a microcomputer platform, and was constructed utilising a commercial object-oriented expert system shell.  相似文献   
994.
A two-stage acid hydrolysis process is currently used in the production of ethanol from hardwoods. In this process, dilute sulfuric acid in water at high pressure and short residence times hydrolyzes the wood and first stage substrate. The chemical action is particularly impeded in the second stage by the presence of acid condensed lignin.

Presulfonation followed by delignification is proposed using a sulfur dioxide/water sulfuric acid/ethanol treatment step in place of the first stage acid hydrolysis step to alleviate this problem.

Results presented include the effects caused by varying treatment time, sulfur dioxide concentration, temperature and ethanol concentration on the degree of delignification, and, on the recovery of C5 and C6 sugars in the hydrolysates. A preliminary economic feasibility analysis is made to determine the impact of improved ethanol yields and lignin by-product values in the production of ethanol from hardwoods.  相似文献   
995.
996.
A control and management network for wireless ATM systems   总被引:1,自引:0,他引:1  
This paper describes the design of a control and management network (orderwire) for a mobile wireless Asynchronous Transfer Mode (ATM) network. This mobile wireless ATM network is part of the Rapidly Deployable Radio Network (RDRN). The orderwire system consists of a packet radio network which overlays the mobile wireless ATM network. Each network element in this network uses Global Positioning System (GPS) information to control a beamforming antenna subsystem which provides for spatial reuse. This paper also proposes a novel Virtual Network Configuration (VNC) algorithm for predictive network configuration. A mobile ATM Private Network–Network Interface (PNNI) based on VNC is also discussed. Finally, as a prelude to the system implementation, results of a Maisie simulation of the orderwire system are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
997.
Psychopathy in instrumental and reactive violent offenders.   总被引:1,自引:0,他引:1  
Can violent offenders who commit acts of instrumental aggression for goal-oriented purposes such as robbery be distinguished from those who commit acts of reactive (or hostile) aggression in response to provocation? Because violent offenders often have a history of both instrumental and reactive aggression, this study distinguished between offenders with a history of at least 1 instrumental violent offense and offenders with a history of reactive violent offenses. Two studies tested the hypothesis that instrumental offenders would score higher than reactive offenders and nonviolent offenders on R. D. Hare's (1991) Psychopathy Checklist. The first study sample consisted of 106 violent and nonviolent offenders recruited from a medium-security correctional facility. The second study sample consisted of 50 violent offenders referred for pretrial forensic evaluation. In both samples, instrumental offenders could be reliably distinguished from reactive offenders on the basis of violent crime behavior and level of psychopathy. Group differences could not be attributed to participant age, race, length of incarceration, or extent of prior criminal record. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
998.
The effect of injection into the medial septum of a toxin selective for cholinergic neurons, 192 IgG-saporin, was examined in rats trained to perform 2 versions of the radial 8-arm maze task. Rats were first trained to perform a task with varying delays (0, 1, 2 min) imposed between the 4th correct arm choice and access to all 8 arms. Lesioned rats made significantly more errors in the first 4 choices compared with controls and significantly more errors after delays; however, this effect was not delay dependent. Rats were then trained on a different version of this 8-arm maze task in which they learned to avoid 2 arms that were never baited. There was no treatment effect on acquisition of this task. These data are consistent with the hypothesis that the cholinergic projection to the hippocampus facilitates the acquisition of information into the system responsible for short-term memory for locations visited (spatial working memory) but is not involved in retention of this information. It also appears to play no role in either the acquisition or retention of place-nonreward associations (spatial reference memory). (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
999.
The ability of dose combinations of cholecystokinin (CCK) and bombesin to inhibit liquid glucose (0.125 gm/ml) intake and affect microstructural components of ingestive behavior in rats was examined. Five min before access to the glucose solution, rats were injected with dose pairs of CCK and bombesin. Both CCK and bombesin inhibited intake in a dose-related fashion. The magnitude of the inhibition produced by dose combinations was never greater than the sum of the inhibitions produced by the individual doses. CCK and bombesin affected different microstructural components of ingestion. CCK reduced burst size and cluster size, whereas bombesin reduced burst number and cluster number. These effects of the 2 peptides were not altered by the presence of the other peptide. These results suggest that different mechanisms of action underlie the feeding inhibitory actions of the 2 peptides. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
1000.
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