全文获取类型
收费全文 | 50086篇 |
免费 | 1766篇 |
国内免费 | 88篇 |
专业分类
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 |
出版年
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.
McWayne Christine M.; Fantuzzo John W.; McDermott Paul A. 《Canadian Metallurgical Quarterly》2004,40(4):633
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.
Mohsen Ghazel George H Freeman Edward R Vrscay 《IEEE transactions on image processing》2006,15(9):2669-2675
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.
Shamachary Sathish John H. Cantrell William T. Yost 《Journal of the American Ceramic Society》1996,79(1):209-212
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.
John C. Hart Gordon W. Lescinsky Daniel J. Sandin Thomas A. DeFanti Louis H. Kauffman 《The Visual computer》1993,9(7):346-355
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.
George V. Eleftheriades Gabriel M. Rebeiz 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(10):1925-1946
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