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   50086篇
  免费   1766篇
  国内免费   88篇
电工技术   555篇
综合类   61篇
化学工业   10753篇
金属工艺   1270篇
机械仪表   940篇
建筑科学   2574篇
矿业工程   323篇
能源动力   1532篇
轻工业   4047篇
水利工程   540篇
石油天然气   316篇
武器工业   2篇
无线电   3245篇
一般工业技术   8469篇
冶金工业   9552篇
原子能技术   436篇
自动化技术   7325篇
  2022年   360篇
  2021年   728篇
  2020年   606篇
  2019年   704篇
  2018年   850篇
  2017年   855篇
  2016年   947篇
  2015年   796篇
  2014年   1266篇
  2013年   3353篇
  2012年   2042篇
  2011年   2687篇
  2010年   1943篇
  2009年   2038篇
  2008年   2302篇
  2007年   2235篇
  2006年   1967篇
  2005年   1800篇
  2004年   1585篇
  2003年   1490篇
  2002年   1475篇
  2001年   914篇
  2000年   874篇
  1999年   834篇
  1998年   928篇
  1997年   784篇
  1996年   855篇
  1995年   771篇
  1994年   772篇
  1993年   731篇
  1992年   678篇
  1991年   461篇
  1990年   582篇
  1989年   608篇
  1988年   513篇
  1987年   578篇
  1986年   531篇
  1985年   698篇
  1984年   685篇
  1983年   592篇
  1982年   613篇
  1981年   562篇
  1980年   469篇
  1979年   478篇
  1978年   430篇
  1977年   422篇
  1976年   377篇
  1975年   414篇
  1974年   341篇
  1973年   356篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
51.
The present concurrent study combined developmental and ecological considerations to examine the unique contribution of multiple preschool competencies to an indicator of early academic success. Participants included 195 Head Start children from 32 classrooms representative of a large, urban Head Start program. Dimensional (variable-centered) analyses revealed 3 distinct classroom competency dimensions (i.e., General Classroom Competencies, Specific Approaches to Learning, and Interpersonal Classroom Behavioral Problems). The first 2 of these dimensions were found to be uniquely associated with early academic success. Findings from typological (person-centered) analyses supported the dimensional findings. Typological analyses revealed 7 profiles of classroom competency distinguished by high scores on the dimensions of General Competencies and Approaches to Learning, and these profiles were found to relate differentially to the indicator of early academic success. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
52.
The essence of fractal image denoising is to predict the fractal code of a noiseless image from its noisy observation. From the predicted fractal code, one can generate an estimate of the original image. We show how well fractal-wavelet denoising predicts parent wavelet subtress of the noiseless image. The performance of various fractal-wavelet denoising schemes (e.g., fixed partitioning, quadtree partitioning) is compared to that of some standard wavelet thresholding methods. We also examine the use of cycle spinning in fractal-based image denoising for the purpose enhancing the denoised estimates. Our experimental results show that these fractal-based image denoising methods are quite competitive with standard wavelet thresholding methods for image denoising. Finally, we compare the performance of the pixel- and wavelet-based fractal denoising schemes.  相似文献   
53.
A revised methodology is described for research on metacognitive monitoring, especially judgments of learning (JOLs), to investigate psychological processing that previously has been only hypothetical and unobservable. During data collection a new stage of recall occurs just prior to the JOL, so that during data analysis the items can be partitioned into subcategories to measure the degree of JOL accuracy in ways that are more analytic than was previously possible. A weighted-average combinatorial rule allows the component measures of JOL accuracy to be combined into the usual overall measure of metacognitive accuracy. An example using the revised methodology offers a new explanation for the delayed-JOL effect, in which delayed JOLs are more accurate than immediate JOLs for predicting recall. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
54.
55.
56.
Scanning acoustic microscopy of SCS-6 silicon carbide fiber reveals large radial variations in acoustic reflectivity associated with the chemical composition and microstructure of a given fiber region. Rayleigh wave fringe patterns observed in each of five subregions are used to calculate the average Young modulus of that subregion. The Young modulus is found to increase monotonically from 40 GPa in the carbon core to a value of 413 GPa in the stoichiometric SiC region. The effective Young modulus of the fiber as a whole is estimated from the moduli of the individual regions and it is compared with mechanical measurements reported in the literature.  相似文献   
57.
58.
59.
The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well.  相似文献   
60.
In this paper, an efficient implementation of the spectral domain moment technique is presented for computing the self and mutual coupling between slot antennas on a dielectric half-space. It is demonstrated that by the proper selection of the weighting functions in the method of moments, the analytic evaluation or simplification of the transverse moment integrals is enabled. This results into a significant reduction of the required computational labor. The method is then utilized in order to provide design data for the self and mutual admittances between two slot antennas on a dielectric substrate lens in the case of fused quartz (∈ r =3.80), crystal quartz (∈ r =4.53), silicon (∈ r =11.9) and GaAs (∈ r =12.8). The presented technique and associated results are useful when designing twin slot quasi-optical receivers, imaging arrays, phased arrays or power-combining arrays of slot elements at millimeter-wave frequencies.  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