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   298956篇
  免费   24054篇
  国内免费   15379篇
电工技术   17499篇
技术理论   54篇
综合类   39152篇
化学工业   39814篇
金属工艺   15080篇
机械仪表   15471篇
建筑科学   40101篇
矿业工程   15569篇
能源动力   8452篇
轻工业   19160篇
水利工程   14316篇
石油天然气   13391篇
武器工业   2998篇
无线电   18080篇
一般工业技术   23742篇
冶金工业   17908篇
原子能技术   2837篇
自动化技术   34765篇
  2024年   626篇
  2023年   2775篇
  2022年   5466篇
  2021年   6891篇
  2020年   7035篇
  2019年   5996篇
  2018年   5734篇
  2017年   7101篇
  2016年   8341篇
  2015年   9410篇
  2014年   16412篇
  2013年   15130篇
  2012年   19929篇
  2011年   21350篇
  2010年   16895篇
  2009年   17640篇
  2008年   16151篇
  2007年   21500篇
  2006年   20299篇
  2005年   17785篇
  2004年   15090篇
  2003年   13585篇
  2002年   11264篇
  2001年   9480篇
  2000年   8009篇
  1999年   6606篇
  1998年   5079篇
  1997年   4346篇
  1996年   4012篇
  1995年   3354篇
  1994年   3006篇
  1993年   2208篇
  1992年   1967篇
  1991年   1434篇
  1990年   1219篇
  1989年   1063篇
  1988年   849篇
  1987年   575篇
  1986年   421篇
  1985年   364篇
  1984年   343篇
  1983年   256篇
  1982年   225篇
  1981年   171篇
  1980年   136篇
  1979年   115篇
  1978年   62篇
  1977年   72篇
  1976年   56篇
  1975年   56篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
浅谈图书馆网站的建设   总被引:4,自引:0,他引:4  
弓品云  谢辉  马东明 《电力学报》2003,18(2):163-165
对我国现阶段公共图书馆网站的总体情况进行了分析和概括 ,列举了具有代表性的几个网站的主要特点 ,指出了存在的问题 ,提出了相应的对策 ,强调了网站建设首先应有以读者需要为依归的理念 ,并将之贯穿在网站的内容设置和页面设计的整个过程中。  相似文献   
992.
Fumio Negoro 《Knowledge》2003,16(7-8):383-397
The purpose of our study is to build up relationships between requirement and source programs with our originally thought-out rules. When other rules to be derived from these original rules are applied to software development, even a single instruction in a programming language could be determined, and the program would satisfy the requirement. More specifically speaking, these rules will turn into a formula or a prototype of software programs. Hence, when the variables in the requirement are placed in the formula, we can get a required program in an automatic way.  相似文献   
993.
本文通过对线缆外护套材料在我国西部地区严酷环境试验站中土壤和大气1~5年的试验结果分析,总结了塑料护套材料的耐蚀性能。为线缆护套的防护设计、合理选材及制定标准提供科学依据。  相似文献   
994.
对耐火材料——棕刚玉粉的质量分析控制,提出了用实用性的检测方法测定其Al2O3含量。通过与国家标准分析方法的对比试验,证实快速实用分析方法测定棕刚玉粉中Al2O3含量是可行的。  相似文献   
995.
借鉴英国经验完善中国土地产权流转   总被引:1,自引:0,他引:1  
本文在简要介绍中、英两国土地产权制度和土地产权流转的基础上,分析了我国土地产权流转过程中出现的问题,如征地过程中的赔偿过低且不完善、国有土地拆迁补偿不公以及补偿的分配方式不公平等问题。由于英国在土地制度方面与中国的相似性,文章借鉴英国土地补偿中的补偿金与改善金相结合原则、土地使用权的租赁行为以及开发收益回馈社会的方法,为完善和健全我国的土地产权流转机制提出措施和建议。  相似文献   
996.
Modafinil is indicated for the management of excessive daytime sleepiness; however, recent studies have examined a broad range of potential uses. Given that clinical uses of modafinil may be expanding, this study compared modafinil and d-amphetamine effects on subjective and performance measures. Across 11 sessions, 11 healthy adults were tested after oral doses of placebo (5 sessions), modafinil (1.75 mg/kg, 3.50 mg/kg, or 7.00 mg/kg), and d-amphetamine (0.035 mg/kg, 0.070 mg/kg, 0.140 mg/kg) under double-blind, randomized conditions. Assessments of cognitive performance and subjective effects were completed before drug administration, 30 min after drug administration, and at hourly intervals after drug administration for 5 hr. Modafinil increased ratings on the Amphetamine and Morphine Benzedrine Group scales of the Addiction Research Center Inventory (ARCI) and increased ratings on the Vigor and Total Positive scales of the Profile of Mood States. d-Amphetamine increased visual analog ratings of feeling stimulated and liking the drug and increased ratings on the Morphine Benzedrine Group scale of the ARCI. Both medications significantly reduced visual analog scale ratings of feeling sleepy, and modafinil decreased ratings on the ARCI Pentobarbital-Chlorpromazine-Alcohol Group scale. Both medications sustained performance that deteriorated across time on the Sternberg Number Recognition Test. Modafinil also enhanced performance rate on the Digit-Symbol Substitution Task above baseline levels and increased response rate on the Repeated Acquisition of Response Sequences Task. These results suggest that modafinil engenders alerting effects and increases performance in healthy non-sleep-deprived individuals comparable with that of d-amphetamine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
997.
This study investigated the Stages of Change Readiness and Treatment Eagerness Scale (SOCRATES: W. R. Miller & J. S. Tonigan, 1996) in adolescents presenting for treatment of alcohol use disorder (AUD). The participants were 80 males and 43 females (mean age=16.8 years) who presented for AUD treatment (95.1% outpatient, 4.9% inpatient). Participants completed assessments at baseline and 1 year and provided information on alcohol use and related variables monthly between these 2 assessments. Principal-components and confirmatory factor analyses of the baseline SOCRATES identified 2 factors, Taking Steps and Recognition, which showed good internal consistency and concurrent and predictive evidence of validity. The results were interpreted as supporting the use of the SOCRATES with clinical samples of adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
998.
天然植物香精油的开发利用   总被引:6,自引:0,他引:6  
王岚 《中国油脂》2003,28(12):86-89
天然植物香精油产业是一项新兴产业,满足了人们崇尚自然、追求健康的需要,具有很好的经济效益和社会效益。对天然植物香精油从用途、国内外现状、采用技术等几方面进行了阐述,得出了适用于植物香精油的最佳工艺技术和流程,采用了目前较先进的冷冻干燥技术和超临界CO2萃取技术,得到的产品具有萃取效率高、品质好等优点。  相似文献   
999.
When modern saloon cars are re-engineered as convertibles (or roadsters) it is typical for them to lose 50% or more of the body’s torsional rigidity. Consequently the vehicles rarely handle quite as crisply, nor do they ride as well as the coupes from which they derived. This paper highlights the fundamental contributions of advanced composites in achieving the desired value of handling of the Murcièlago Roadster without penalizing the overall weight of the vehicle. To compensate for the absence of the roof structure, the vehicle was strongly redesigned by introducing new structural members and reinforcing existing critical components. A new all-carbon/epoxy composite sub-frame, which spans the entire engine bay, is comprised of elliptical tubular members, and it is the first of its kind in a production vehicle. Engineering of the sub-frame, from preliminary design to manufacturing decisions, is the focus of this paper, and is achieved through a Building Block approach that sets the program within the Integrated Product Development (IPD) strategy that the Advanced Composites Division of Automobili Lamborghini S.p.A. employs for its technology demonstrators. The strategy consists in a concurrent analytical and experimental development of the product, from the initial conceptual design and coupon testing, through the stages of element and subcomponent engineering, to final component manufacturing.  相似文献   
1000.
Resin cure following mold filling is an essential element in resin transfer molding. To fabricate a composite part with high dimensional stability and minimize residual stress, uniform resin cure should be achieved. This study considers a three-part resin system composed of epoxy, hardener and accelerator. The cure kinetics can be controlled by the accelerator concentration at the injection gate. A numerical method that can predict degree of cure distribution based on accelerator concentration at the gate was proposed. The degree of cure distribution is obtained by solving the resin flow, heat transfer, accelerator concentration and cure problems sequentially. Utilizing this numerical method, an optimal variation of accelerator concentration during mold filling was sought by solving a constrained optimization problem. The effect of accelerator control on degree of cure distribution was investigated and its validity was examined for two different geometries.  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