全文获取类型
收费全文 | 73808篇 |
免费 | 10169篇 |
国内免费 | 8389篇 |
专业分类
化学 | 40464篇 |
晶体学 | 781篇 |
力学 | 2709篇 |
综合类 | 528篇 |
数学 | 6394篇 |
物理学 | 18576篇 |
无线电 | 22914篇 |
出版年
2024年 | 261篇 |
2023年 | 1483篇 |
2022年 | 2094篇 |
2021年 | 2617篇 |
2020年 | 2450篇 |
2019年 | 2478篇 |
2018年 | 2154篇 |
2017年 | 2290篇 |
2016年 | 2931篇 |
2015年 | 3229篇 |
2014年 | 3976篇 |
2013年 | 5010篇 |
2012年 | 5971篇 |
2011年 | 6172篇 |
2010年 | 4796篇 |
2009年 | 4829篇 |
2008年 | 5083篇 |
2007年 | 4707篇 |
2006年 | 4392篇 |
2005年 | 3686篇 |
2004年 | 2814篇 |
2003年 | 2333篇 |
2002年 | 2218篇 |
2001年 | 1871篇 |
2000年 | 1612篇 |
1999年 | 1450篇 |
1998年 | 1184篇 |
1997年 | 1057篇 |
1996年 | 997篇 |
1995年 | 881篇 |
1994年 | 819篇 |
1993年 | 680篇 |
1992年 | 624篇 |
1991年 | 546篇 |
1990年 | 454篇 |
1989年 | 336篇 |
1988年 | 285篇 |
1987年 | 203篇 |
1986年 | 225篇 |
1985年 | 226篇 |
1984年 | 139篇 |
1983年 | 95篇 |
1982年 | 102篇 |
1981年 | 66篇 |
1980年 | 65篇 |
1979年 | 71篇 |
1978年 | 54篇 |
1976年 | 47篇 |
1974年 | 49篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Y.K. Su H.C. Wang C.L. Lin W.B. Chen S.M. Chen 《Photonics Technology Letters, IEEE》2003,15(10):1345-1347
The brightness of AlGaInP light emitting diodes (LEDs) has been raised by a factor of 1.12 at 20 mA by sulfide passivation. Meanwhile, the sulfide also can decrease leakage current of AlGaInP LEDs at -2 V to nearly one thousandth of that in the as-fabricated device. The possible causes for the brightness increase of AlGaInP LEDs after sulfide treatment including surface roughness, reduction of Fresnel loss, and effective injection of carriers were demonstrated. 相似文献
32.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。 相似文献
33.
Min-Shiang Hwang Chih-Wei Lin Cheng-Chi Lee 《Electronics letters》2002,38(23):1429-1431
An authenticated multiple-key agreement protocol is proposed. The protocol is not only secure against the unknown-key attack but also more efficient than other protocols. 相似文献
34.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
35.
Coplanar waveguide-fed uniplanar bow-tie antenna 总被引:3,自引:0,他引:3
Yu-De Lin Syh-Nan Tsai 《Antennas and Propagation, IEEE Transactions on》1997,45(2):305-306
The design of coplanar waveguide (CPW)-fed bow-tie antenna for the 2.4-GHz ISM band is described. A coplanar waveguide-to-coplanar strips (CPW-to-CPS) balun is used to obtain the balanced feed line for the printed bow-tie. An analysis method based on the mixed potential integral equation method is used to characterize the input characteristics of the bow-tie antenna. The numerical results obtained are in good agreement with the experimental data. Through experiments with bow-tie antennas of various extended angles, the bow-tie antenna with a 90° extended angle exhibits the widest bandwidth in the desired frequency band which has a bandwidth of 17% for a VSWR <1.5:1 相似文献
36.
Color image retrieval based on hidden Markov models 总被引:1,自引:0,他引:1
In this correspondence, a new approach to retrieving images from a color image database is proposed. Each image in the database is represented by a two-dimensional pseudo-hidden Markov model (2-D PHMM), which characterizes the chromatic and spatial information about the image. In addition, a flexible pictorial querying method is used, by which users can paint the rough content of the desired images in a query picture. Image matching is achieved by comparing the query picture with each 2-D PHMM in the database. Experimental results show that the proposed approach is indeed effective. 相似文献
37.
Horng-Dar Lin 《Circuits and Devices Magazine, IEEE》1995,11(4):25-31
Identifies the basic technological components of multimedia communications. Among these technologies, multimedia processing and transmission already benefit heavily from VLSI advances. in fact, these two technologies could not have matured without special-purpose VLSI chips. We have examined basic processing required in these technologies and some VLSI architectures. The focus has been on standard-compliant VLSI chips, because the eventual goal of communications is to allow everyone to reach others without constraints. There are still a number of evolving standards, which means that we might witness yet another wave of VLSI chips for multimedia communications 相似文献
38.
Yoshiaki Murata Cheng-Huang Lin Totaro Imasaka 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):543-544
Summary A supersonic jet spectrum of 9,10-dichloroanthracene is measured by stimulated-emission-pumping fluorescence dip spectrometry and conventional fluorescence spectrometry. The performance obtained is compared for these spectrometric methods, providing same information concerned with the energy level of the ground state. The former is more preferential for measurement of a high-resolution spectrum, since the spectral resolution is determined by the linewidth of the dumping laser. On the other hand, the latter is more preferential for measurement with better sensitivity at the expense of the spectral resolution, since the fluorescence throughput can be improved by increasing the slit width of the monochromator.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
39.
本文报导了最近研制成功的用于提高国产氩离子激光器相干长度的相干扩展器。利用这种基于F-P理论的相干扩展器可以使国产氩离子激光器的相干长度由不足5cm一下提高到m的量级,功率损耗在25%~40%之间,有着很好的应用前景。 相似文献
40.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献