全文获取类型
收费全文 | 8823篇 |
免费 | 436篇 |
国内免费 | 81篇 |
专业分类
电工技术 | 194篇 |
综合类 | 89篇 |
化学工业 | 1621篇 |
金属工艺 | 218篇 |
机械仪表 | 296篇 |
建筑科学 | 351篇 |
矿业工程 | 13篇 |
能源动力 | 279篇 |
轻工业 | 463篇 |
水利工程 | 38篇 |
石油天然气 | 44篇 |
武器工业 | 2篇 |
无线电 | 1762篇 |
一般工业技术 | 1595篇 |
冶金工业 | 1214篇 |
原子能技术 | 88篇 |
自动化技术 | 1073篇 |
出版年
2023年 | 94篇 |
2022年 | 136篇 |
2021年 | 192篇 |
2020年 | 147篇 |
2019年 | 131篇 |
2018年 | 193篇 |
2017年 | 192篇 |
2016年 | 192篇 |
2015年 | 195篇 |
2014年 | 289篇 |
2013年 | 536篇 |
2012年 | 445篇 |
2011年 | 484篇 |
2010年 | 385篇 |
2009年 | 446篇 |
2008年 | 451篇 |
2007年 | 409篇 |
2006年 | 376篇 |
2005年 | 320篇 |
2004年 | 301篇 |
2003年 | 304篇 |
2002年 | 255篇 |
2001年 | 230篇 |
2000年 | 212篇 |
1999年 | 197篇 |
1998年 | 469篇 |
1997年 | 314篇 |
1996年 | 218篇 |
1995年 | 144篇 |
1994年 | 125篇 |
1993年 | 146篇 |
1992年 | 82篇 |
1991年 | 79篇 |
1990年 | 70篇 |
1989年 | 50篇 |
1988年 | 53篇 |
1987年 | 54篇 |
1986年 | 59篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 20篇 |
1981年 | 40篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 26篇 |
1977年 | 40篇 |
1976年 | 43篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1971年 | 12篇 |
排序方式: 共有9340条查询结果,搜索用时 0 毫秒
41.
42.
Our previous receiver operating characteristic (ROC) study indicated that the detection accuracy of microcalcifications by radiologists is significantly reduced if mammograms are digitized at 0.1 mm x 0.1 mm. Our recent study also showed that detection accuracy by computer decreases as the pixel size increases from 0.035 mm x 0.035 mm. It is evident that very large matrix sizes have to be used for digitizing mammograms in order to preserve the information in the image. Efficient compression techniques will be needed to facilitate communication and archiving of digital mammograms. In this study, we evaluated two compression techniques: full frame discrete cosine transform (DCT) with entropy coding and Laplacian pyramid hierarchical coding (LPHC). The dependence of their efficiency on the compression parameters was investigated. The techniques were compared in terms of the trade-off between the bit rate and the detection accuracy of subtle microcalcifications by an automated detection algorithm. The mean-square errors in the reconstructed images were determined and the visual quality of the error images was examined. It was found that with the LPHC method, the highest compression ratio achieved without a significant degradation in the detectability was 3.6:1. The full frame DCT method with entropy coding provided a higher compression efficiency of 9.6:1 at comparable detection accuracy. The mean-square errors did not correlate with the detection accuracy of the microcalcifications. This study demonstrated the importance of determining the quality of the decompressed images by the specific requirements of the task for which the decompressed images are to be used. Further investigation is needed for selection of optimal compression technique for digital mammograms. 相似文献
43.
L Chan 《Canadian Metallurgical Quarterly》1995,6(5):335-340
Genetic manipulations of experimental animals have provided valuable information on lipoprotein metabolism in vivo. Somatic gene transfer is a novel method for introducing foreign genes into animals in vivo. Adenovirus-mediated transfer of genes for the LDL receptor, the receptor-associated protein, apolipoprotein A-I, apolipoprotein E, cholesterol 7 alpha-hydroxylase, and apolipoprotein B messenger RNA editing protein has resulted in high-level expression of these transgenes in mice and hamsters, and the production of interesting animal models of lipoprotein metabolism. Somatic gene transfer is a valuable tool for analyzing the role of transgenes in lipoprotein metabolism in vivo and for exploring the potential use of specific transgenes for human gene therapy. 相似文献
44.
We have examined the applicability of this simple and effective test to polymer systems widely used in the medical industry. First, it was found that not every polymer examined exhibited a distinct onset of autocatalytic oxidation detectable by DSC. However, for cases where distinct onsets are found, powerful insights can be obtained. These included activation energy of the degradation, thermal oxidative shelf life prediction, and correlation, with product performances. Actual examples are presented to illustrate the utility of the test. 相似文献
45.
A quartz microbalance technique has been used to study the growth of4He and H2 adsorbed on sodium. In contrast to cesium, adsorption of4He and H2 do occur on a sodium surface. 相似文献
46.
Charles A. Bateman Lijie Zhang Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1992,75(5):1281-1283
It is experimentally observed that the peritectic reaction, 211 + liquid → 123, can be driven essentially to completion in 1 h at an undercooling of only ∽30°C. The kinetic data, together with the observed microstructures, are inconsistent with the normal mechanism of the peritectic reaction. It is proposed that the mechanism of the reaction involves dissolution of 211 particles into the liquid and precipitation of solid 123. The aligned grain structure is explained through sympathetic nucleation of new 123 grains on existing grains. 相似文献
47.
钢结构稳定设计——理论与实践 总被引:2,自引:0,他引:2
本文提出了实际工程结构的非线性理论设计和分析方法(NIDA),并以澳门回归纪念馆的设计为例,展示了本方法的优越性.在设计过程中,设计者无需假设K系数和有效长度,在结构分析完成后便可迅速完成设计,因此本文提出的方法既经济又便利.尽管对于钢框架在往复荷载及动力荷载作用下的弹塑性大位移分析已经非常成熟,但本文的方法开创了结构的非线性分析及设计的新纪元,能够对现行的设计方法理论起到巨大的推动作用. 相似文献
48.
Chan T.H. Yeung R.W. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(7):1992-1995
We establish a one-to-one correspondence between information inequalities and group inequalities. The major implication of our result is that we can prove information inequalities by proving the corresponding group inequalities, and vice versa. By giving a group-theoretic proof for all Shannon-type inequalities, we suggest that new inequalities could be discovered by making use of the rich set of tools in group theory. On the other hand, via a non-Shannon-type information inequality discovered by Zhang and Yeung (1997), we obtain a new inequality in group theory whose meaning is yet to be understood 相似文献
49.
A hybrid PC/PLC architecture for manufacturing-system control—theory and implementation 总被引:1,自引:0,他引:1
A. Ramirez-Serrano S. C. Zhu S. K. H. Chan S. S. W. Chan M. Ficocelli B. Benhabib 《Journal of Intelligent Manufacturing》2002,13(4):261-281
This paper presents a novel and generic PC/PLC-based software/hardware architecture for the control of flexible manufacturing workcells. The proposed implementation methodology is based on the utilization of any one of the available formal discrete-event-system control theories in conjunction with state-of-the-art industrial programmable-logic controllers (PLCs). The methodology has been illustrated to be a viable technique through its actual implementation in our laboratory using a robotic-workcell testbed. The specific control theory used is a combination of Extended Moore Automata and Ramadge-Wonham Automata that has been developed by our research group. The modular control software architecture has been developed for MS-Windows environments (running on one PC interfaced to the PLCs) and allows the use of different formal control theories as well as different commercial PLC hardware. The effective graphical user interface provides a transparent programming environment, where users are not expected to have a full knowledge of the formal control theory used. 相似文献
50.