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   519篇
  免费   33篇
  国内免费   49篇
电工技术   13篇
综合类   23篇
化学工业   39篇
金属工艺   51篇
机械仪表   11篇
建筑科学   25篇
矿业工程   58篇
能源动力   7篇
轻工业   33篇
水利工程   36篇
石油天然气   33篇
无线电   10篇
一般工业技术   26篇
冶金工业   198篇
原子能技术   12篇
自动化技术   26篇
  2024年   1篇
  2023年   5篇
  2022年   19篇
  2021年   21篇
  2020年   24篇
  2019年   20篇
  2018年   13篇
  2017年   9篇
  2016年   11篇
  2015年   8篇
  2014年   19篇
  2013年   27篇
  2012年   27篇
  2011年   43篇
  2010年   25篇
  2009年   32篇
  2008年   35篇
  2007年   31篇
  2006年   31篇
  2005年   33篇
  2004年   39篇
  2003年   30篇
  2002年   24篇
  2001年   24篇
  2000年   8篇
  1999年   8篇
  1998年   7篇
  1997年   5篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1992年   1篇
  1991年   1篇
  1989年   1篇
  1987年   3篇
  1986年   1篇
  1981年   1篇
  1967年   2篇
  1964年   1篇
  1963年   1篇
  1957年   1篇
  1956年   1篇
排序方式: 共有601条查询结果,搜索用时 390 毫秒
41.
Maternal smoking is a leading preventable cause of poor pregnancy outcomes and infant morbidity and mortality. Whereas pregnancy has been thought of as a "window of opportunity" when women are more motivated to change health behaviors such as smoking, only 20% of pregnant women quit smoking upon learning they are pregnant and remain abstinent at the end of the pregnancy. Greater understanding of possible obstacles to smoking during pregnancy, such as nicotine withdrawal, is needed. The symptoms of nicotine withdrawal have been well characterized in nonpregnant smokers, but there has been only 1 report conducted during pregnancy, and that was a retrospective study. The aim of the present study was to characterize nicotine withdrawal and craving in pregnant cigarette smokers. These data were collected as part of prospective clinical trials assessing the efficacy of voucher-based incentives to promote abstinence from cigarette smoking during pregnancy and postpartum. The authors examined results from the Minnesota Nicotine Withdrawal Scale (J. R. Hughes & D. K. Hatsukami, 1998) in 27 abstainers (reported no or very low levels of smoking, which was confirmed biochemically) and 21 smokers (smoked at >80% of their baseline smoking level) during the first 5 days of a cessation attempt. Abstainers reported more impatience, anger, and difficulty concentrating than did smokers. The results also suggest that pregnant smokers generally may have elevated baseline levels of withdrawal, which need to be considered in the design and analysis of future studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
42.
实现国有资本从生产领域主动、有序地退出,是国有经济战略性调整至关重要的一步.从近年来地方政府大规模转让国有资产的情形来看,国有资产的定价依据、转让程序等的规范性、公允性尚有令人质疑之处.本文认为,中国通过构建3方(中央、省、地市)负责、3层(国资委、控股公司、企业)架构的国资管理体系,让国有控股公司承担国有资本的营运责任,由它自主组织国有资本的退出、进入.同时,政府要营造良好的退出环境,健全保障体系,采取有力的措施提高市场的接盘能力,为了防范国有资产的大量流失、保护投资者的利益,政府宜充分发挥中介机构、大众媒体的监督作用.  相似文献   
43.
HIV medication adherence remains a challenge and limits the degree to which treatment benefit can be maximized. This study tested an explanatory model of HIV medication adherence using a social problem-solving (SPS) framework. Associations of SPS with adherence are hypothesized to be direct and/or indirect via psychological health. HIV+ adults were interviewed using validated measures of SPS, psychological health, and antiretroviral therapy (ART) medication adherence. Structural equation modeling (SEM) techniques were used to test hypothesized relationships and to evaluate overall fit of the model to the data. SEM supported an indirect association (but not direct) of SPS on adherence via psychological health among the 545 HIV+ adults included in the analyses. Overall, the findings resulted in a model of adherence that offered very good fit to the data and correctly classified 97% of the cases as adherent versus nonadherent. Results support the use of SPS as a conceptual framework for understanding adherence to ART. Findings offer rationale and direction for SPS interventions to enhance adherence by improving psychological health. Such approaches, if effective, have the potential to positively impact psychological well being and adherence, thereby maximizing clinical benefit from treatment, which is linked to lower mortality from AIDS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
44.
Although treatment with transdermal nicotine replacement (TNR) has improved smoking abstinence rates, higher doses of TNR could improve effects on urge to smoke, nicotine withdrawal, and reinforcement from smoking, and naltrexone might further reduce reinforcement and urges. A laboratory investigation with 134 smokers using a 3 × 2 parallel-group design evaluated the effects of TNR (42-mg, 21-mg, or 0-mg patch) as crossed with a single dose of naltrexone (50 mg) versus placebo on urge to smoke, withdrawal, and responses to an opportunity to smoke (intake, subjective effects) after 10 hr of deprivation. Urge and withdrawal were assessed both prior to and after cigarette cue exposure. Only 42 mg TNR, not 21 mg, prevented urge to smoke, heart rate change, and cue-elicited increase in withdrawal. Both 21 and 42 mg TNR blocked cue-elicited drop in heart rate and arterial pressure. Naltrexone reduced cue-elicited withdrawal symptoms but not urges to smoke or deprivation-induced withdrawal prior to cue exposure. Neither medication significantly affected carbon monoxide intake or subjective effects of smoking except that 42 mg TNR resulted in lower subjective physiological activation. No interaction effects were found, and no results differed by gender. Results suggest that starting smokers with 42 mg TNR may increase comfort during initial abstinence, but limited support is seen for naltrexone during smoking abstinence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
45.
随着国家环保要求日益严格,冶炼厂对工艺技术进行了改造和提升,工艺和装备水平有了明显的改进和提高,然而在冶炼技术方面的弱点也越来越突出。本着有利于发展产业集群,促进地方经济增长,保护水资源,严格执行最严格水资源管理制度,促进水资源合理开发利用和节约用水,保障经济社会可持续发展的理念,以某冶炼厂为例探讨冶炼厂用水工艺及合理用水量,为冶炼厂用水合理性分析提供参考。  相似文献   
46.
由高血压引起的心脑血管疾病已成为中国人的首位死因,对高血压病人进行长期治疗是控制血压的一种有效手段.为了发现高血压病人是否坚持服药和血压值之间的关系,首先根据高血压病人的电子处方记录鉴定出不坚持服药的病人,然后将Apriori算法应用于病人电子处方记录并挖掘出有意义的规则.实验结果表明,大约三分之二不坚持服药的病人不能...  相似文献   
47.
New data support use of levodopa pharmacotherapy with behavioral contingency management (CM) as one efficacious combination in cocaine dependence disorder treatment. A potential mechanism of the combined treatment effects may be related to dopamine-induced enhancement of the saliency of contingently delivered reinforcers. Evidence to support this mechanism was sought by evaluating levodopa-enhancing effects across distinct CM conditions that varied in behavioral targets. A total of 136 treatment-seeking, cocaine dependent subjects participated in this 12-week, randomized, placebo-controlled trial of levodopa (vs. placebo) administered in combination with one of three behavioral CM conditions. In the CM-URINE condition, subjects received cash-valued vouchers contingent on cocaine-negative urine toxicology results. In the CM-ATTEND condition, the same voucher schedule was contingent on attending thrice weekly clinic visits. In the CM-MEDICATION condition, the same voucher schedule was contingent on Medication Event Monitoring Systems- and riboflavin-based evidence of pill-taking behavior. Primary outcomes associated with each CM target behavior were analyzed using generalized linear mixed models for repeated outcomes. CM responding in the CM-ATTEND and CM-MEDICATION conditions showed orderly effects, with each condition producing corresponding changes in targeted behaviors, regardless of medication condition. In contrast, CM responding in the CM-URINE condition was moderated by medication, with levodopa-treated subjects more likely to submit cocaine-negative urines. These findings specify the optimal target behavior for CM when used in combination with levodopa pharmacotherapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
48.
To analyze the withdrawal force curve in the wetting balance curve, wetting balance tests using the 63Sn-37Pb and 96.5Sn-3.6Ag eutectic solders were conducted by varying the immersion speed, sample perimeter, and solder temperature. The mechanism of the withdrawal force curve was reviewed and a new method for calculating the surface tension of solders using the withdrawal force curve was introduced. The results showed that the maximum point of the withdrawal force curve is generated when the sliding solder meets the bottom corners of a sample and the contact angle is reduced to zero. The maximum withdrawal force subtracted by end force can be expressed using force balance equation as F=pγ. Therefore, the surface tension of the solder can be calculated by dividing the maximum withdrawal force by the sample parameter.  相似文献   
49.
The land subsidence spreading factor χ provides a useful straightforward indication on how much of a gas/oil reservoir compaction induced by field development migrates to ground surface with a possible adverse impact on the stability of low‐lying coastal areas. This factor depends primarily on the ratio between the depth of burial and a representative horizontal dimension of the reservoir. However, an important influence is also exerted by the active bottom/lateral aquifer hydraulically connected to the field (called “waterdrive” in reservoir engineering) that may undergo an extensive depressurization also after the field abandonment, thus contributing to enhance the overall land settlement. In the Northern Adriatic basin, Italy, χ is evaluated using a nonlinear finite element model of three representative gas reservoirs (Chioggia Mare, Dorotea, and Dosso degli Angeli) surrounded by important bottom/lateral aquifers in the interval depth between 1000 and 3300 m. Results show that χ may easily approach and even exceed one for the deepest field as well, contrary to the prediction of land subsidence based on the compaction of the gas‐bearing formations alone, that can thus be largely underestimated.  相似文献   
50.
Although long-lasting effects of drug withdrawal are thought to play a key role in motivating continued drug use, the mechanisms mediating this type of drug-induced plasticity are unclear. Because Narp is an immediate early gene product that is secreted at synaptic sites and binds to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, it has been implicated in mediating enduring forms of synaptic plasticity. In previous studies, the authors found that Narp is selectively induced by morphine withdrawal in the extended amygdala, a group of limbic nuclei that mediate aversive behavioral responses. Accordingly, in this study, the authors evaluate whether long-term aversive effects of morphine withdrawal are altered in Narp knockout (KO) mice. The authors found that acute physical signs of morphine withdrawal are unaffected by Narp deletion. However, Narp KO mice acquire and sustain more aversive responses to the environment conditioned with morphine withdrawal than do wild type (WT) controls. Paradoxically, Narp KO mice undergo accelerated extinction of this heightened aversive response. Taken together, these studies suggest that Narp modulates both acquisition and extinction of aversive responses to morphine withdrawal and, therefore, may regulate plasticity processes underlying drug addiction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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