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   22398篇
  免费   2356篇
  国内免费   843篇
电工技术   1103篇
技术理论   5篇
综合类   2476篇
化学工业   3225篇
金属工艺   551篇
机械仪表   1357篇
建筑科学   2605篇
矿业工程   282篇
能源动力   466篇
轻工业   1524篇
水利工程   399篇
石油天然气   386篇
武器工业   220篇
无线电   2036篇
一般工业技术   3736篇
冶金工业   318篇
原子能技术   200篇
自动化技术   4708篇
  2024年   372篇
  2023年   571篇
  2022年   826篇
  2021年   994篇
  2020年   744篇
  2019年   614篇
  2018年   599篇
  2017年   752篇
  2016年   833篇
  2015年   873篇
  2014年   1447篇
  2013年   1689篇
  2012年   2043篇
  2011年   1383篇
  2010年   1219篇
  2009年   1342篇
  2008年   1177篇
  2007年   1109篇
  2006年   896篇
  2005年   769篇
  2004年   604篇
  2003年   514篇
  2002年   424篇
  2001年   347篇
  2000年   272篇
  1999年   232篇
  1998年   201篇
  1997年   131篇
  1996年   1143篇
  1995年   532篇
  1994年   394篇
  1993年   57篇
  1992年   60篇
  1991年   57篇
  1990年   45篇
  1989年   39篇
  1988年   42篇
  1987年   31篇
  1986年   31篇
  1985年   39篇
  1984年   47篇
  1983年   19篇
  1982年   17篇
  1981年   15篇
  1980年   13篇
  1978年   10篇
  1977年   7篇
  1976年   5篇
  1973年   3篇
  1959年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Radon变换在倾斜车牌图像校正中的应用   总被引:1,自引:0,他引:1  
倾斜车牌图像的校正是车牌识别中的重要环节之一.根据Radon变换思想,对三种倾斜方式提出了相应的校正方法.用数学形态学的方法对车牌图像进行边缘检测;利用Radon变换检测车牌倾斜角度,对水平方向进行旋转无损校正,对垂直方向进行双线性插值错位偏移校正.实验结果表明该方法是快速有效的.  相似文献   
992.
This work deals with the interference effects recently observed in grazing collisions of few-keV atoms with insulator surfaces. The process is studied within a distorted-wave method, the surface eikonal approximation, based on the use of the eikonal wave function and involving axial channeled trajectories with different initial conditions. The theory is applied to helium atoms impinging on a LiF(0 0 1) surface along the 〈1 1 0〉 direction. The role played by the projectile polarization and the surface rumpling is investigated. We found that when both effects are included, the proposed eikonal approach provides angular projectile spectra in good agreement with the experimental findings.  相似文献   
993.
Scale score measures are ubiquitous in the psychological literature and can be used as both dependent and independent variables in data analysis. Poor reliability of scale score measures leads to inflated standard errors and/or biased estimates, particularly in multivariate analysis. Reliability estimation is usually an integral step to assess data quality in the analysis of scale score data. Cronbach’s α is a widely used indicator of reliability but, due to its rather strong assumptions, can be a poor estimator (L. J. Cronbach, 1951). For longitudinal data, an alternative approach is the simplex method; however, it too requires assumptions that may not hold in practice. One effective approach is an alternative estimator of reliability that relaxes the assumptions of both Cronbach’s α and the simplex estimator and thus generalizes both estimators. Using data from a large-scale panel survey, the benefits of the statistical properties of this estimator are investigated, and its use is illustrated and compared with the more traditional estimators of reliability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
994.
This study investigated episodic memory and metamemory for verbs and nouns in patients who have cognitive impairments associated with Parkinson’s disease (PD). PD patients and healthy control participants were asked to recall word pairs and provide feeling-of-knowing (FOK) judgments for the items they were unable to recall. This was followed by a 4-alternative recognition test. PD patients were impaired in both recall and recognition, compared with controls. In terms of metamemory, PD patients were less confident in their ability to recognize the unrecalled items in a future recognition test. Most important, accuracy of PD patients’ FOK judgments was not above chance and was lower than that of control participants. The PD group correctly recognized fewer verbs than nouns, but type of material (verb vs. noun) had no impact on recall or FOK judgments. In addition, contribution of executive functions to FOK accuracy was different in PD patients and controls. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
995.
This study explored differences in intraindividual variability in 3 attention tasks across a large sample of healthy older adults and individuals with very mild dementia of the Alzheimer’s type (DAT). Three groups of participants (healthy young adults, healthy older adults, very mild DAT) were administered 3 experimental measures of attentional selection and switching (Stroop, Simon, task switching). The results indicated that a measure of intraindividual variability, coefficient of variation (CoV; SD/M), increased across age and early stage DAT. The CoV in Stroop discriminated the performance of ε4 carriers from noncarriers in healthy older controls and the CoV in task switching was correlated with cerebrospinal fluid (CSF) biomarkers predictive of DAT. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
996.
In this article the authors use the imaginal worlds of three children’s stories to explore variations in the affective quality of potential space. Lewis Carroll’s Alice in Wonderland, C. S. Lewis’ The Lion, the Witch, and the Wardrobe, and Norton Juster’s The Phantom Toolbooth, each contain a metaphor of transition in which the protagonist moves from the real space of the narrative into the imaginary space where the action takes place—the protagonists are altered and alter their own worlds. The authors will use these metaphors as analogues to differing qualities of imaginary space, including the collapse of meaning in schizoid states, the play of meaning in mentalization and the adventurousness of negotiating separation. These metaphors of transitioning into imaginary space may be used to think about disruptions in development as they manifest in clinical process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
997.
998.
Due to their high specific strength and stiffness, fibre-reinforced composite materials are being increasingly used in structural applications where a high level of performance is important (e.g. aerospace, automotive, offshore structures, etc.). Performance in service of these composites is affected by multi-mechanism damage evolution under loading and environmental conditions. For instance, carbon fibre-reinforced laminates demonstrate a wide spectrum of failure mechanisms such as matrix cracking and delamination. These damage mechanisms can result in significant deterioration of the residual stiffness and load-bearing capacity of composite components and should be thoroughly investigated. The delamination failure mechanism is studied in this paper for a double cantilever beam (DCB) loaded in mode I. Several sensitivity studies are performed to analyse the effects of mesh density and of parameters of the cohesive law on the character of damage propagation in laminates. The microstructural randomness of laminates that is responsible for non-uniform distributions of stresses in them even under uniform loading conditions is accounted for in the model. The random properties are introduced with the use of Weibull’s two-parameter probability density function. Several statistical realisations are carried out which show that the effect of microstructure could significantly affect the macroscopic response emphasizing the need to account for microstructural randomness for accurate predictions of load-carrying capacity of laminate composite structures.  相似文献   
999.
Purely elastic, partially plastic and fully plastic stress states of internally pressurized functionally graded spherical pressure vessels are investigated analytically in the framework of small deformation theory. The modulus of elasticity and the uniaxial yield limit of the spherical pressure vessel material are assumed to vary nonlinearly in the radial direction. The plastic model is based on Tresca’s yield criterion and ideal plastic material behavior. It is shown that, unlike in the case of a homogeneous spherical pressure vessel, different modes of plasticization may take place due to the radial variation of the functionally grading parameters.  相似文献   
1000.
After a brief history of the Committee on International Relations of the American Psychological Association, 3 points are made about international psychological research that matters. First, it matters when the definition of the research problem area and the findings can potentially be reflected in policy change, in the practice of educators or psychologists, or in the mindsets of a new generation of researchers. Person-centered analysis of adolescents’ social and political attitudes has this potential and can complement variable-centered analysis. A cluster analysis of the IEA Civic Education Study’s data in 5 Western European and 5 Eastern European countries illustrates this. The following 5 clusters of adolescents were identified: those supportive of social justice but not participative, those active in conventional politics and the community, those indifferent, those disaffected, and a problematic cluster of alienated adolescents. Second, research that matters is situated in a cultural context. It is proposed that publications using data from any single country be required to include information about the cultural context in which the research was conducted. Finally, it matters that attention be given to the dynamics of the collaborative international research process, not only to research results. (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