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   2181篇
  免费   38篇
  国内免费   14篇
电工技术   29篇
综合类   3篇
化学工业   481篇
金属工艺   50篇
机械仪表   56篇
建筑科学   88篇
矿业工程   3篇
能源动力   76篇
轻工业   146篇
水利工程   19篇
石油天然气   4篇
无线电   253篇
一般工业技术   433篇
冶金工业   317篇
原子能技术   26篇
自动化技术   249篇
  2022年   17篇
  2021年   32篇
  2020年   20篇
  2019年   31篇
  2018年   23篇
  2017年   23篇
  2016年   20篇
  2015年   24篇
  2014年   46篇
  2013年   112篇
  2012年   80篇
  2011年   94篇
  2010年   95篇
  2009年   94篇
  2008年   107篇
  2007年   98篇
  2006年   73篇
  2005年   92篇
  2004年   53篇
  2003年   57篇
  2002年   63篇
  2001年   35篇
  2000年   39篇
  1999年   54篇
  1998年   126篇
  1997年   72篇
  1996年   64篇
  1995年   46篇
  1994年   34篇
  1993年   34篇
  1992年   26篇
  1991年   20篇
  1990年   17篇
  1989年   32篇
  1988年   27篇
  1987年   33篇
  1986年   15篇
  1985年   29篇
  1984年   23篇
  1983年   22篇
  1982年   22篇
  1981年   24篇
  1980年   24篇
  1979年   13篇
  1977年   18篇
  1976年   25篇
  1975年   10篇
  1974年   10篇
  1973年   9篇
  1971年   10篇
排序方式: 共有2233条查询结果,搜索用时 437 毫秒
21.
The stability of a cracked, nonlinear component connected to an elastic structure and subjected to an arbitrary number of controlled loads or displacements, is discussed. First this is done with a general instability criterion expressed in terms of loads and displacements of the cracked part. Then general expressions for the tearing modulus are given for different loading situations. Finally the given equations are applied to SEN specimens under bending and tension.
Résumé On discute de la stabilité d'un composant fissuré et non linéaire assemblé à une structure élastique et soumis à un monbre quelconque de charges ou de déplacements, appliqués dans des conditions connues. Ceci est réalisé en faisant appel, en premier lieu, à un critère général d'instabilité exprimé en termes the sollicitation et de déplacement de la portion fissurée. Ensuite, on fournit des expressions générales pour le module d'arrachement, correspondant à diverses situations de mise en charge. Enfin, les équations obtenues sont appliquées à des éprouvettes à entaille latérale simple soumises à flexion et traction.
  相似文献   
22.
Structural, mean- and individual-level, differential, and ipsative personality continuity were examined in 599 patients treated for major depression assigned to 1 of 6 forms of a 6-month pharmaco-psychotherapy program. Covariation among traits from the Five Factor model remained invariant across treatment, and patients described themselves as slightly more extraverted, open to experience, agreeable and conscientious, and substantially more emotional stable after treatment. Trait changes were only to a small extent explained by changes in depression severity. There was evidence for differential, individual-level, and ipsative stability, with stable personality profiles in terms of shape and to a lesser extent in terms of scatter and elevation. Traits remain relatively stable, except for emotional stability, despite the depressive state and the psychopharmacological interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
23.
Contends that tests in repeated-measures designs based on MANOVA are free of sphericity assumptions, and with modern computing software, MANOVA is straightforward to use, even for complex designs and nontraditional hypotheses. A general strategy for implementing MANOVA within statistical computing packages is presented. Regular (preplanned) tests and simultaneous (post hoc) tests are illustrated for a variety of designs and hypotheses. Optimal contrasts for unbalanced repeated measures designs are appended. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
24.
Ubiquitin-mediated proteolysis controls the abundance of many cell cycle regulatory proteins. Recent work in Saccharomyces cerevisiae suggests that a complex consisting of Cdc53, Skp1, and a third component known as an F-box protein (termed SCF) in combination with Cdc34 specifically targets regulatory proteins for degradation, and that substrate specificity is likely to be mediated by the F-box subunit. A screen for genetic interactions with a cdc34 mutation yielded MET30, which encodes an F-box protein. MET30 is an essential gene required for cell cycle progression and met30 mutations interact genetically with mutations in SCF components. Furthermore, physical interactions between Met30, Cdc53, Cdc34, and Skp1 in vivo provide evidence for an SCFMet30 complex. We demonstrate the involvement of Met30 in the degradation of the Cdk-inhibitory kinase Swe1. Swe1 is stabilized in met30 mutants and GST-Met30 pull-down experiments reveal that Met30 specifically binds Swe1 in vivo. Furthermore, extracts prepared from cdc34 or met30 mutants are defective in polyubiquitination of Swe1. Taken together, these data suggest that SCF-mediated proteolysis may contribute to the regulation of entry into mitosis. Our data, in combination with previously published results, also provide evidence for distinct SCF complexes in vivo and support the idea that their F-box subunits mediate SCF substrate specificity.  相似文献   
25.
Summary Vinylidene cyanide has been copolymerized in solution by radical reaction with equal initial mole fraction of para substituted acetoxystyrenes. The copolymers have been characterized by means of DSC, TGA and GPC. These products are stable up to 220° and have no visible glass transition temperature. The microstructure of these new copolymers has been studied by 13CNMR; they have an alternating structure and monomers units are arranged in head-to-tail placements.  相似文献   
26.
Aus der Darstellung der Schlackenzusammensetzungen im Quasidreistoffsystem ist die Lage der Schlacken zur Kalksättigungslinie deutlich zu erkennen. Die Sublanzenschlacken lassen den Schlackenweg während der letzten Blasminuten erkennen, durch Bodenspülung und Nachspülen wird eine geringe Annäherung an die Kalksättigungslinie erreicht. Aus der Lage der Schlacken im Quasidreistoffsystem läßt sich der Einfluß der Temperatur auf den Verlauf der Kalksättigung entlang unterschiedlicher T-X-Schnitte bestimmen.  相似文献   
27.
As life expectancy has increased, particularly in developed countries, due to medical advances and increased prosperity, age-related neurological diseases and mental health disorders have become more prevalent health issues, reducing the well-being and quality of life of sufferers and their families. In recent decades, due to reduced work-related levels of physical activity, and key research insights, prescribing adequate exercise has become an innovative strategy to prevent or delay the onset of these pathologies and has been demonstrated to have therapeutic benefits when used as a sole or combination treatment. Recent evidence suggests that the beneficial effects of exercise on the brain are related to several underlying mechanisms related to muscle–brain, liver–brain and gut–brain crosstalk. Therefore, this review aims to summarize the most relevant current knowledge of the impact of exercise on mood disorders and neurodegenerative diseases, and to highlight the established and potential underlying mechanisms involved in exercise–brain communication and their benefits for physiology and brain function.  相似文献   
28.
This note considers the problem of local stability of bilinear systems with aperiodic sampled-data linear state feedback control. The sampling intervals are time-varying and upper bounded. It is shown that the feasibility of some linear matrix inequalities (LMIs), implies the local asymptotic stability of the sampled-data system in an ellipsoidal region containing the equilibrium. The method is based on the analysis of contractive invariant sets, and it is inspired by the dissipativity theory. The results are illustrated by means of numerical examples.  相似文献   
29.
This study aims to determine whether indirect touch device can be used to interact with graphical objects displayed on another screen in an air traffic control (ATC) context. The introduction of such a device likely requires an adaptation of the sensory-motor system. The operator has to simultaneously perform movements on the horizontal plane while assessing them on the vertical plane. Thirty-six right-handed participants performed movement training with either constant or variable practice and with or without visual feedback of the displacement of their actions. Participants then performed a test phase without visual feedback. Performance improved in both practice conditions, but accuracy was higher with visual feedback. During the test phase, movement time was longer for those who had practiced with feedback, suggesting an element of dependency. However, this ‘cost’ of feedback did not extend to movement accuracy. Finally, participants who had received variable training performed better in the test phase, but accuracy was still unsatisfactory. We conclude that continuous visual feedback on the stylus position is necessary if tablets are to be introduced in ATC.  相似文献   
30.
InNauphoeta cinerea, male calling behavior is associated with sex pheromone release by the sternal glands. The male pheromone that attracts females from a distance is a mixture of 2-methylthiazolidine and 4-ethylguaiacol. It is active at very low concentrations, 0.05 and 0.01 ng, respectively. Two other compounds, 3-hydroxy-2-butanone and 2-methyl-2thiazoline, act at close range, keeping the female in the vicinity of the male. The function of the volatile pheromone and those of previously described contact pheromones are discussed in regard to their possible involvement in the establishment of male dominant-subordinate relationships.  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