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   704篇
  免费   43篇
电工技术   2篇
化学工业   213篇
金属工艺   14篇
机械仪表   20篇
建筑科学   21篇
矿业工程   3篇
能源动力   20篇
轻工业   183篇
水利工程   3篇
石油天然气   2篇
无线电   24篇
一般工业技术   98篇
冶金工业   101篇
自动化技术   43篇
  2023年   5篇
  2022年   22篇
  2021年   58篇
  2020年   22篇
  2019年   19篇
  2018年   38篇
  2017年   15篇
  2016年   24篇
  2015年   14篇
  2014年   25篇
  2013年   46篇
  2012年   25篇
  2011年   41篇
  2010年   42篇
  2009年   36篇
  2008年   59篇
  2007年   59篇
  2006年   32篇
  2005年   22篇
  2004年   20篇
  2003年   12篇
  2002年   11篇
  2001年   8篇
  2000年   4篇
  1999年   9篇
  1998年   11篇
  1997年   7篇
  1996年   5篇
  1995年   7篇
  1992年   7篇
  1991年   3篇
  1990年   3篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   4篇
  1981年   2篇
  1979年   1篇
  1978年   1篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1967年   3篇
  1966年   1篇
  1964年   1篇
  1962年   1篇
  1956年   1篇
  1936年   1篇
排序方式: 共有747条查询结果,搜索用时 819 毫秒
51.
The effectiveness of electrospinning as a simple approach to disperse POSS into a polymer matrix at a nm‐level has been assessed. Electrospun and cast films were prepared by dissolving CA and epoxycyclohexylisobutyl POSS in the solvent mixture acetone/DMAc. The membranes were characterized by SEM, TEM and WAXD. Whereas films produced by casting showed µm‐sized POSS crystals, thus suggesting a small affinity between the polymer matrix and the POSS molecules, those prepared by electrospinning were characterized by a nanometric POSS distribution. This is explained by considering the peculiar solvent evaporation mechanism, occurring during the electrospinning process, which allows to produce nanofibers characterized by a silsesquioxane dispersion similar to that present in solution.

  相似文献   

52.
The Alternaria toxins alternariol (AOH; 3,7,9-trihydroxy-1-methyl-6H-benzo[c]chromen-6-one) and alternariol methyl ether (AME, 3,7-dihydroxy-9-methoxy-1-methyl-6H-benzo[c]chromen-6-one) are common contaminants of food and feed, but their oxidative metabolism in mammals is as yet unknown. We have therefore incubated AME and AOH with microsomes from rat, human, and porcine liver and analyzed the microsomal metabolites with HPLC and GC-MS/MS. Seven oxidative metabolites of AME and five of AOH were detected. Their chemical structures were derived from their mass spectra using deuterated trimethylsilyl (TMS) derivatives, and from the information obtained from enzymatic methylation. Several of the metabolites were identified by comparison with synthetic reference compounds. AME as well as AOH were monohydroxylated at each of the four possible aromatic carbon atoms and also at the methyl group. In addition, AME was demethylated to AOH and dihydroxylated to a small extent. As the four metabolites arising through aromatic hydroxylation of AME and AOH are either catechols or hydroquinones, the oxidative metabolism of these mycotoxins may be of toxicological significance.  相似文献   
53.
The proportion of sustainable property in the total building stock remains small. One reason is that the financial added value resulting from sustainability is not sufficiently taken into account in property valuation due to the tendency of valuations to lag behind market trends. Quantitative information is provided to integrate those aspects of sustainability relating to value into valuations and thereby contribute to the reduction of valuation lag. The Centre for Corporate Responsibility and Sustainability (CCRS) Economic Sustainability Indicator (ESI) measures the risk of property to lose value and the opportunity to gain value due to future developments (e.g. climate change or rising energy prices). Five groups of value-related sustainability features were identified: flexibility and polyvalence; energy and water dependency; accessibility and mobility; security; and health and comfort. By minimizing the risk of loss in value through future developments, those sustainability features contribute to the property value. Their effects on property value were quantified by risk modelling. As an indicator for future-oriented property risk, the ESI is integrated into the discount rate of discounted cash flow valuations. The approach was tested for plausibility and practicability on more than 200 properties.

La proportion de biens immobiliers durables dans le parc immobilier total demeure faible. L'explication tient pour une part au fait que la valeur ajoutée financière résultant de la durabilité n'est pas suffisamment prise en compte dans l'évaluation des biens immobiliers en raison du fait que les évaluations tendent à avoir du retard sur les tendances du marché. Des informations quantitatives sont fournies afin d'intégrer les aspects de la durabilité liés à la valeur dans les évaluations et de contribuer ainsi à la réduction du retard dans les évaluations. L'Indicateur de Durabilité Economique (ESI) du Centre pour la Responsabilité et la Durabilité en Entreprise (CCRS) mesure le risque de perte de valeur des biens immobiliers et la possibilité d'en accroître la valeur du fait des évolutions futures (par ex. changement climatique et hausse des prix énergétiques). Cinq groupes de fonctions de durabilité liées à la valeur ont été identifiés: flexibilité et polyvalence, dépendance vis-à-vis de l'énergie et de l'eau; accessibilité et mobilité; sécurité; santé et confort. En minimisant le risque d'une perte de valeur causée par les évolutions futures, ces fonctions de durabilité contribuent à la valeur des biens immobiliers. Leurs effets sur la valeur des biens immobiliers ont été quantifiés par une modélisation des risques. En tant qu'indicateur du risque prospectif pour les biens immobiliers, l'ESI est intégré au taux d'actualisation des flux de trésorerie actualisés. Cette approche a été testée quant à sa plausibilité et sa praticabilité sur plus de 200 biens immobiliers.

Mots clés: flux de trésorerie actualisés, indicateur de durabilité économique, évaluation des biens immobiliers, modèle de risque, fonctions de durabilité, durabilité, bâtiments durables  相似文献   
54.
Objective: Marital discord has been linked to both depression and anxiety; however, our understanding of how marriage contributes to the development of internalizing symptoms is limited in scope and lacking specificity. First, it is unclear whether the marital relationship contributes to the broad dimension of internalizing symptoms as opposed to specific diagnoses. Second, it is unclear how the marital relationship contributes to internalizing symptoms: through global marital dissatisfaction or through specific relationship processes (and which processes). The purpose of the present study was to address these 2 issues and, more generally, to develop a comprehensive and refined framework within which to understand the role of marriage in the developmental course of internalizing symptoms. Method: Questionnaire and interview data were collected from 102 husbands and wives 5 times over the first 7 years of marriage. Results: Results indicated that marital discord during the transition into marriage was associated with the broad dimension of internalizing symptoms for husbands but not for wives. Further, both global marital dissatisfaction and an imbalance of power and control put husbands at significant risk for symptoms over the first 7 years of marriage, whereas low levels of emotional intimacy put wives at significant risk. Conclusions: Results exemplify the need to routinely consider intimate relationship processes in etiological models of depression and anxiety and to identify specific clinical targets that can be prioritized in interventions aimed at preventing internalizing disorders. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
55.
Pineal gland melatonin is the darkness hormone, while extra-pineal melatonin produced by the gonads, gut, retina, and immune competent cells acts as a paracrine or autocrine mediator. The well-known immunomodulatory effect of melatonin is observed either as an endocrine, a paracrine or an autocrine response. In mammals, nuclear translocation of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) blocks noradrenaline-induced melatonin synthesis in pinealocytes, which induces melatonin synthesis in macrophages. In addition, melatonin reduces NF-κB activation in pinealocytes and immune competent cells. Therefore, pathogen- or danger-associated molecular patterns transiently switch the synthesis of melatonin from pinealocytes to immune competent cells, and as the response progresses melatonin inhibition of NF-κB activity leads these cells to a more quiescent state. The opposite effect of NF-κB in pinealocytes and immune competent cells is due to different NF-κB dimers recruited in each phase of the defense response. This coordinated shift of the source of melatonin driven by NF-κB is called the immune-pineal axis. Finally, we discuss how this concept might be relevant to a better understanding of pathological conditions with impaired melatonin rhythms and hope it opens new horizons for the research of side effects of melatonin-based therapies.  相似文献   
56.
Particulate-filled composites were prepared from CaCO 3 and polymer matrices of various acid-base characters. Interfacial interaction of the components was characterized by the reversible work of adhesion, which was calculated either from dipole-dipole or acid-base interactions. The thickness of the spontaneously formed interlayer was derived from the tensile strength of the composites. The results proved that acid-base interactions play an important role in interphase formation. The strength of interfacial adhesion is determined by the joint effect of dispersion forces and acid-base interactions. Stronger interaction leads to a thicker interphase with decreased mobility. Treatment of CaCO 3 with an aliphatic fatty acid leads to a decrease in the strength of interaction, and to changes both in the thickness and properties of the interphase. In composites containing coated fillers, acid-base interactions influence composite properties less due to the neutral character of the surface.  相似文献   
57.
This study examines the relationship among global coping self-efficacy, coping, and coping effectiveness within athletes. We hypothesized that there would be a positive association between coping self-efficacy and coping effectiveness, which would be mediated by coping. It was also predicted that coping strategies within the task-oriented coping dimension would be positively associated with coping effectiveness, whereas strategies from the disengagement- and distraction-oriented coping dimensions would be negatively associated with coping effectiveness. Participants were 353 athletes between the ages of 18 and 29 years, who completed a measure of coping self-efficacy the night before they competed, in addition to a measure of the athletes' use of coping strategies and their perceived coping effectiveness, which was completed immediately after the competitive event. Results revealed that higher global coping self-efficacy scores were significantly (r = .33, p  相似文献   
58.
A comprehensive evolutionary personality psychology can be developed by identifying individual differences within each of the evolved systems that regulate social behaviour. We developed a questionnaire measure of social rank style, defined as individual differences in preferred strategies for pursuing, defending, and, when necessary, relinquishing social rank. The 17-item Rank Style with Peers Questionnaire (RSPQ) comprises three nearly independent scales: dominant leadership, coalition-building, and ruthless self-advancement. A series of studies demonstrated that: (a) the RSPQ’s, factor structure is robust; (b) the three rank style variables are not redundant with the five-factor traits or adult attachment styles; (c) they are related in theoretically expected ways to adjustment outcomes, to agentic and communal interpersonal behaviours, and to social reputations; (d) they predict group and individual performance outcomes relevant to organisational psychology; and (e) they are related in theoretically expected ways to psychopathology, including social anxiety disorder and depressive symptoms. Future directions for research on social rank styles and prospects for an evolutionary personality psychology are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
59.
The identification of both approved and non-approved genetically modified organisms (GMOs) is an integral part of GMO biosafety legislation in many countries. One aspect that may affect PCR-based detection of a GMO lies within the analysis of its genetic stability, as sequence alterations or DNA instabilities may impede quantification by PCR. Genetic stability can be analyzed using various methods, yet many of these methods have distinct disadvantages, including low sensitivity. In this study, high resolution melting (HRM) analysis and real-time PCR with Scorpion primers were used as a method to analyze the 3′ end of RR soybeans (RR 40-3-2) in a large number of samples (n = 1,034). No evidence for the occurrence of mutation events was found, implying that the nucleotide sequence of this region is unlikely to be unstable and is well suited as a target for the quantification of RR soybeans. Additionally, and as a preparative work for an optimization of the method, a 174 bp region of the first intron of the Adh1 gene was analyzed in several varieties of maize with different GMO events using the same approach. The results show that 2 alleles are present. In further experiments, the different alleles were cloned into plasmids to generate homozygous plasmids from heterozygous templates in order to generate for a more precise analysis. The overall methodological aim of these studies was to compare HRM analysis with Scorpion primer PCR. Both methods were capable of differentiating between the 2 homozygous and heterozygous alleles. For a better discrimination, however, we conclude that it is most reliable to consider the results of both methods. This dual approach is assumed to be an effective tool as an accurate, high-throughput means of the screening of GMOs for potential genetic instabilities that may interfere with the detection and identification of specific GM events.  相似文献   
60.
This article discusses the evaluation of flashing yellow as an off-peak traffic signal control strategy by establishing an interface between a real-time traffic simulation software HUTSIM (Helsinki University of Technology Simulation Model) and a standard NEMA (National Electrical Manufacturers Association) traffic signal controller. The analysis was performed as part of research dealing with evaluation of different off-peak traffic signal operation strategies and their relative impacts on delay, fuel consumption, vehicle emissions, and driver safety. Because of its widespread use, the main emphasis was on the flashing yellow signal control. Delay field study was performed to obtain and analyze real-world data and compare the efficiency of flashing yellow and fixed time control strategies. To widen the research effort and eliminate inaccuracies due to certain assumptions made during the field study, computer simulation was chosen as an effective tool for comparison of different control strategies. Four different strategies were evaluated: fixed time, fully and semiactuated, and flashing yellow. Flashing yellow was found to be the most efficient of the signal strategies. The impact of this type of off-peak signal control on driver safety also was studied, and a summary of results is presented.  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