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   66662篇
  免费   5031篇
  国内免费   2179篇
电工技术   2567篇
技术理论   8篇
综合类   4491篇
化学工业   14115篇
金属工艺   8707篇
机械仪表   3420篇
建筑科学   7867篇
矿业工程   2395篇
能源动力   1440篇
轻工业   6259篇
水利工程   2573篇
石油天然气   2410篇
武器工业   778篇
无线电   1947篇
一般工业技术   6847篇
冶金工业   5706篇
原子能技术   448篇
自动化技术   1894篇
  2024年   280篇
  2023年   782篇
  2022年   1623篇
  2021年   1967篇
  2020年   1979篇
  2019年   1438篇
  2018年   1516篇
  2017年   1932篇
  2016年   2072篇
  2015年   2236篇
  2014年   3757篇
  2013年   3813篇
  2012年   4746篇
  2011年   5082篇
  2010年   4101篇
  2009年   4031篇
  2008年   3348篇
  2007年   4445篇
  2006年   4343篇
  2005年   3554篇
  2004年   2956篇
  2003年   2720篇
  2002年   2207篇
  2001年   1771篇
  2000年   1434篇
  1999年   1127篇
  1998年   885篇
  1997年   685篇
  1996年   583篇
  1995年   519篇
  1994年   398篇
  1993年   277篇
  1992年   250篇
  1991年   192篇
  1990年   143篇
  1989年   156篇
  1988年   92篇
  1987年   79篇
  1986年   54篇
  1985年   55篇
  1984年   52篇
  1983年   42篇
  1982年   32篇
  1981年   7篇
  1980年   15篇
  1979年   7篇
  1966年   9篇
  1965年   8篇
  1964年   9篇
  1959年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The need for better protecting our vital infrastructure from being damaged or destroyed has received increased attention since the terrorist attacks on September 11, 2001. The tragedy of having thousands of innocent people die before the eyes of an entire nation awakened people to the reality of “managed” attacks of unthinkable magnitudes. However, tragedies of a smaller scale are a daily occurrence but accepted as “collateral damage” of work in an unsafe environment. This paper presents a cost-benefit analysis to address the question of how much money should be spent in protecting underground utilities from damage. During the study of an actual incident it was found that the total costs of such accidents are vastly underreported because only costs for emergency responses and repair are tallied up. This paper makes the case that a comprehensive approach for assessing the total economic impact of such incidents on the public, business, and government is the critical stepping stone to a mathematical optimization of expenditure for damage prevention. In addition, the reader will quickly realize that the use of the presented optimization model provides theoretical underpinning for the engineering profession in its effort to better protect our critical infrastructure from terrorist attacks.  相似文献   
52.
The ability to accurately and reliably predict whether an older adult will commit suicide has eluded clinicians and researchers. A random national sample of psychologists who work with older adults was surveyed regarding their perception of 36 risk factors for completed suicide and indirect self-destructive behavior in older adults. This study produced a profile of psychologists' assessment and treatment practices when working with suicidal older adults. Determining what psychologists consider to be the most salient risk factors for completed suicide is important in identifying a minimum standard that clinicians should follow when assessing older adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
53.
The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H2S and SO2 in humid air at 25 °C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 °C or with ammonia/steam at 800 °C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption-regeneration cycles showed important differences between oxidative retention of H2S and SO2 and the subsequent catalyst/support regeneration process.  相似文献   
54.
概述污水处理厂的一般工艺,简单介绍了风机、水泵等的节能特点,介绍了变频调速装置在污水处理厂各处理工段的应用。  相似文献   
55.
This study investigated the relationship between self-appraisals of performance, symptom severity and post-event rumination in social phobia, and evaluated the effect of treatment on these variables. A socially phobic group and a nonanxious control group performed an impromptu speech and were told that their performance would be evaluated. Participants appraised their performance immediately after the speech and 1 week later, and the frequency of post-event rumination during the week following the speech was assessed. The socially phobic group maintained the negative appraisals of their speech over the week, whereas the nonclinical group showed increased positivity about their performance The socially phobic group also engaged in more negative rumination than controls. Treatment improved perceptions of performance and reduced negative rumination. These results are discussed in the light of cognitive models of social phobia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
通过模型试验 ,对位于西安市东郊因采沙使河道破坏严重的灞河河段进行了复现试验和研究 ,并以此为依据 ,通过优化比较为设计部门提供了合理的橡胶坝坝址和坝座高程。在此基础上 ,又对建坝后橡胶坝对上下游冲淤变化的影响进行了试验研究和分析 ,解决了工程设计中的一些关键技术问题  相似文献   
57.
Nanosized powders of single-phase zinc gallate (ZnGa2O4) spinel were hydrothermally synthesized from solutions in the presence of NaOH over the pH range of 1.9 to 7.0 and from solutions above pH 7.0, i.e., the very basic medium (pH of 13.85), by removing the residual ZnO phase by washing with aqueous H2SO4 from the precipitate mixtures of zinc gallate spinel particles and ZnO. A very wide compositional range (Zn/2Ga = 0.705–1.157) of zinc gallate spinel solid solutions could be hydrothermally synthesized in the form of nanosized particles from acid and very basic mediums (pH of 2.4–13.85) in the presence of NaOH. These hydrothermally synthesized spinel powders showed good sinterability and almost full densification at 1100°C for 1 h. Dense sintered bodies consisting of single-phase zinc gallate spinel were fabricated at 1100°C using zinc gallate spinel powders having almost stoichiometric composition formed from the solution at pH 9.95 in the presence of aqueous ammonia.  相似文献   
58.
采用二甲苯为溶剂,将不同乙烯含量(5% ̄15%质量)的抗冲聚丙烯用特定程序进行分级,将各样品分为室温下可溶于甲苯和不可溶于甲苯的两部分。使用^13C-NMR方法和FT-IR方法对各组分进行表征,明确了乙烯链段在聚丙烯链上的分布,并在此基础上提出了产生这种链结构的聚合工艺的特点。  相似文献   
59.
The goal of the present studies was to construct and validate a short form of the 50-item Smoking Consequences Questionnaire (SCQ; T. H. Brandon & T. B. Baker, 1991), a measure of smoking outcome expectancies. In Study 1, a 21-item short form (S-SCQ) was derived from a sample of 107 young adults previously treated for substance abuse. In Study 2, the measure was cross-validated on 125 adolescents in treatment for substance abuse. Confirmatory factor analyses revealed good model fit and factorial invariance for the 4 S-SCQ subscales across both samples. Validation analyses on each sample found that subscale scores generally correlated significantly with smoking-related variables. The present studies provide initial evidence for the utility of the S-SCQ when used with young adults and adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
60.
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