全文获取类型
收费全文 | 189篇 |
免费 | 34篇 |
国内免费 | 54篇 |
专业分类
系统科学 | 23篇 |
丛书文集 | 2篇 |
教育与普及 | 1篇 |
现状及发展 | 4篇 |
研究方法 | 9篇 |
综合类 | 238篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 19篇 |
2013年 | 16篇 |
2012年 | 17篇 |
2011年 | 10篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 29篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 31篇 |
2004年 | 19篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1989年 | 2篇 |
排序方式: 共有277条查询结果,搜索用时 15 毫秒
61.
LI Shitao QIAO Xueliang CHEN Jianguo JIA Fang WU Changle 《北京科技大学学报》2006,28(8):743-743
Tin-doped indium oxide (ITO) thin films were prepared using conventional radio frequency (RF) planar magnetron sputtering equipped with IR irradiation using a ceramic target of In2O3/SnO2 with a mass ratio of 1:1 at various IR irradiation temperatures T1 (from room temperature to 400 ℃ ). The refractive index, deposited ratio, and resistivity are functions of the sputtering Ar gas pressure. The microstructure of ITO thin films is related to IR T are amorphous at the temperature ranging from 1, the crystalline seeds appear at T1 = 300℃, and the films 27 ℃ to 400 ℃. 相似文献
62.
Digital watermarking has been proposed for the copyright protections of multimedia products. In this paper, a robust and blind watermarking scheme is presented. The concept of communication with side in-formation is applied at the encoder to improve the probability of detection within acceptable fidelity, while the template matching technique is employed to estimate the undergone attacks in attacking channel. This scheme is optimized by the optimal design of the encoder to match with the media content and the decoder to adapt to the attack channel state. Experiments show that our method is robust against some common at-tacks such as filtering, compression, rotation, scaling, cropping and translation. It can be applied to both color and gray images. 相似文献
63.
Biological properties were studied to appropriate pathogenic bacteria which were isolated from diseased (or dead) stone flounder (Kareius bicoloratus L. ) which expressed bacterial septicaemia, including morphological characteristics, colony characteristics, physiological and biochemical characteristics and serum homology of isolates, the results showed that the isolates belonged to a new subspecies of A. salmonicida. In addition, the representative strains have been re-checked and detected the mol% G C ratio of the DNA by China Center for Type Culture Collection (CCTCC), the examined strains were also regarded as a new subspecies of A. salmonicida, and designated as Aeromonas salmonicida subsp, flounderac/da subsp, nov. by its isolated fish (Kareius bicoloratus ). Molecular identification of analysis of the nucleotide sequence of the 16S rRNA gene were applied, the results showed high similarity (99%) with the 16S rRNA gene of Aeromonas salmonicida from GenBank database. Cluster analysis of phylogenetic tree revealed that the representative strain formed separately bootstrap-supported cluster. 相似文献
64.
Single-negative properties of Ba2Co1.8Cu0.2Fe12O22 and Ba3Co2Fe23.4Zn0.6O41 hexagonal ferrites 下载免费PDF全文
The electromagnetic properties of Ba2Co1.8Cu0.2Fe12O22 (Co2Y) and Ba3Co2Fe23.4Zn0.6O41 (Co2Z) were studied by measuring microwave scattering parameters. In the transmission spectra of Ba2Co1.8Cu0.2Fe12O22, a forbidden band emerges due to ferromagnetic resonance, and the permeability will turn to negative in the vicinity of the ferromagnetic resonance frequency. In the complex permittivity spectra of Ba3Co2Fe23.4Zn0.6O41, the negative permittivity can be obtained due to dielectric resonance. Therefore, Co2Y and Co2Z can be used to construct left-handed materials possessing negative permeability and negative permittivity simultaneously. 相似文献
65.
We study the dynamics of two entangled atoms interacting with a common structured reservoir. By means of the exact solution of atomic dynamics, we show a novel quantum interference controlled by the relative phase of initial entangled state of the atoms. The quantum interference has a great influence on trapped excited-state population and stationary entanglement of the atoms. In particular, we construct an explicit condition under which atomic stationary entanglement can grow over their initial value. 相似文献
66.
基于线粒体COI基因序列探讨长江华溪蟹的遗传分化 总被引:6,自引:0,他引:6
测定了长江华溪蟹3个亚种,包括指名亚种,桐柏亚种和陕县亚种共39个样本的线粒体细胞色素氧化酶亚基I(COI)基因部分的序列.重建的系统发生结果显示,长江华溪蟹分化成2个分支,一支代表雄性第1腹肢末节呈平直型的指名亚种支;另一支则代表雄性第1腹肢末节弯向背内方的内弯型支,包括稍向内弯的桐柏亚种和明显内弯的陕县亚种在内.在内弯型支内,桐柏亚种和陕县亚种之间的遗传距离为0.018,是两大分支间的1/10.提示长江华溪蟹COI基因的遗传分化与其雄性第1腹肢末节弯曲程度的形态分化基本一致. 相似文献
67.
Effect of vacuum annealing on the characteristics of composite pellets containing DBSA-doped polyaniline and Fe nanoparticles 下载免费PDF全文
The DBSA-PANI-Fe composite powder with 50wt% of Fe nanoparticles was prepared by mechanically mixing the DBSA-doped polyaniline powder and Fe nanoparticles. The composite powder was compacted to pellets and the pellets were annealed in vacuum at 443,493,543, and 593 K for 60 and 120 min. The conductivity of the pellet increases markedly with increasing the annealing temperature up to 493 K, and then decreases with further increasing the annealing temperature. When the pellet was annealed at 493 K for 60 min, the increment of conductivity reaches a maximum value, and the conductivity is 2.6 times as large as that of the pellet unannealed. The conductivities of the pellets annealed under the conditions of 543 K/120 min, 593 K/60 min, and 593 K/120 min are lower than the conductivity of the pellet unannealed. For all the pellets, the variation in conductivity with temperature reveals that the charge transport mechanism can be considered to be 1-D variable-range-hopping (1-D VRH). The composite pellet shows a magnetic hysteresis loop independent of the annealing condition. The saturation magnetization is about 5.4×104 emu/kg. The saturation field and the coercivity are estimated to be 4.38×105 and 3.06×104 A/m, respectively. The crystalline structure ofFe nanoparticles in the composites does not change with the annealing condition. The annealing condition cannot destroy the polymer backbones. 相似文献
68.
The mRNA differential display (DDRT-PCR) technique was adopted to find out the genes related to settlement metamorphosis development process of Ruditapes philippinarum larvae. In this study, we have obtained three hundred and forty-six amplification bands in total from pediveliger larvae, veliger larvae, eye spot larvae and post-larvae. Sixty-five out of three hundred and forty-six bands are distinctly differential display from band pattern, which can be put into four groups, standing for different expression characters. Sixteen differential display bands were cloned, sequenced and analyzed and nine different sequences are obtained in the study. Three sequences have higher similarity to the cDNAs deposited in database and three are very similar to the rDNA of other species, considered as the rDNA of Ruditapes philippi narum. The rest three sequences are found to be novel sequences after analyzed. Their accession numbers are AY916799, AY916798, and AY916797 respectively. We thought the novel sequences are possibly relevant to the early embryo development of Ruditapes philippinarum larvae and can provide some fundamental understandings that are helpful for the improvement of scallop seed raising industry. 相似文献
69.
The latest progress in the multiuser detection and independent component analysis (ICA) is reviewed systematically. Then two novel classes of multiuser detection methods based on ICA algorithms and feedforward neural networks are proposed. Theoretical analysis and computer simulation show that ICA algorithms are effective to detect multiuser signals in code-division multiple-access (CDMA) system. The performances of these methods are not identical entirely in various channels, but all of them are robust, efficient, fast and suitable for real-time implementations. 相似文献
70.
In this article,current application,materials,key equipments,finite element(FE) simulation and parts properties of hot stamping are introduced.The investigations of all processes and further excellent processes are described.The survey of existing works,especially key equipments has revealed several gaps.Some new ideas and programs are proposed on the basis of traditional process.This article aims at providing an insight into a whole process backgrounds and pointing out the great potential for further investigations and innovations of hot stamping. 相似文献