全文获取类型
收费全文 | 87491篇 |
免费 | 8616篇 |
国内免费 | 5324篇 |
专业分类
电工技术 | 5811篇 |
技术理论 | 7篇 |
综合类 | 7777篇 |
化学工业 | 13647篇 |
金属工艺 | 4678篇 |
机械仪表 | 5222篇 |
建筑科学 | 6579篇 |
矿业工程 | 2387篇 |
能源动力 | 2260篇 |
轻工业 | 9966篇 |
水利工程 | 2234篇 |
石油天然气 | 3695篇 |
武器工业 | 835篇 |
无线电 | 9925篇 |
一般工业技术 | 9166篇 |
冶金工业 | 3164篇 |
原子能技术 | 1016篇 |
自动化技术 | 13062篇 |
出版年
2024年 | 527篇 |
2023年 | 1590篇 |
2022年 | 3081篇 |
2021年 | 4020篇 |
2020年 | 3218篇 |
2019年 | 2395篇 |
2018年 | 2629篇 |
2017年 | 3057篇 |
2016年 | 2700篇 |
2015年 | 3993篇 |
2014年 | 5121篇 |
2013年 | 6047篇 |
2012年 | 6739篇 |
2011年 | 7191篇 |
2010年 | 6465篇 |
2009年 | 5897篇 |
2008年 | 5847篇 |
2007年 | 5483篇 |
2006年 | 4945篇 |
2005年 | 3930篇 |
2004年 | 2778篇 |
2003年 | 2406篇 |
2002年 | 2523篇 |
2001年 | 2110篇 |
2000年 | 1458篇 |
1999年 | 1239篇 |
1998年 | 788篇 |
1997年 | 654篇 |
1996年 | 594篇 |
1995年 | 419篇 |
1994年 | 345篇 |
1993年 | 252篇 |
1992年 | 233篇 |
1991年 | 168篇 |
1990年 | 121篇 |
1989年 | 98篇 |
1988年 | 71篇 |
1987年 | 47篇 |
1986年 | 52篇 |
1985年 | 17篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 32篇 |
1979年 | 17篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1959年 | 9篇 |
1951年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
41.
Feding Ge Jing Zhu Limin Chen 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(2):449-455
The effective parameters of chiral composite are studied using a simple model, that is, randomly oriented non-interacting wire helices embedded in a nonchiral host medium. It is found that both the effective permittivity ? and permeability μ are independent on the handedness of the chiral objects while the effective chirality admittance ξ is dependent. It is also found that when the ratio of the radius of the chiral helix to its pitch is about 0.23, maximum chirality admittance is achieved. The effective parameters of equichiral sample are also discussed. 相似文献
42.
Thin CdTe films were deposited by hot-wall epitaxy (HWE) on (111) HgCdTe and CdZnTe substrates at temperatures from about 140 to 335°C. X-ray rocking curves were used to show that crystal quality of the CdTe (111)B films improved as substrate temperature increased from 140 to about 250°C. Rocking curve values for full width at half maximum (FWHM) decreased from 2–4 degrees at 140–150°C to less than 100 arc-s at 250°C, and a FWHM of 59 arc-s was the lowest value observed near 250°C. The FWHM of the HWE CdTe was found to be insensitive to growth rate below about 400Å/min, but increased to four degrees at 1250Å/min. X-ray diffraction confirmed that films grown on the B-face at higher temperatures were epitaxial, but contained a significant volume fraction, 35% to 50%, of rotational in-plane twins. Electron microscopy confirmed a coarse twin density, and photoluminescence spectra showed an absence of excitonic emission in the HWE films. Simultaneous growth on two (111) HgCdTe substrates with different surface polarities between 230°C and 335°C showed that deposition rate on the A-face decreased relative to that on the B-face as temperature increased. Films grown on the B-face exhibited better surface morphologies than those grown on the A-face. 相似文献
43.
Fanggao Chang Tao Li Yongxia Ge Zhenping Chen Zhongshi Liu Xiping Jing 《Journal of Materials Science》2007,42(17):7109-7115
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x
Ho
x
)TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x
Ho
x
)TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The
local electron density and defect concentration estimated using positron annihilation technique conforms well to the features
found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model. 相似文献
44.
45.
结合海河流域防汛会商系统的开发情况,对防汛会商系统的功能、技术进行了详细的说明,对今后防汛会商系统开发及改进具有借鉴意义. 相似文献
46.
K.F. Chan C.K. Wan K.N. Yu 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,262(1):128-134
In the present work, we have studied the feasibility of a method based on polyallyldiglycol-carbonate (PADC) films to investigate the effects of alpha particles on HeLa cervix cancer cells. Thin PADC films with thickness of about 20 μm were prepared from commercially available CR-39 films by chemical etching to fabricate custom-made petri dishes for cell culture, which could accurately record alpha particle hit positions. A special method involving “base tracks” for aligning the images of cell nuclei and alpha particle hits has been proposed, so that alpha particle transversals of cell nuclei can be visually counted. Radiobiological experiments were carried out to induce DNA damages, with the TdT-mediated dUTP Nick-End Labeling (TUNEL) fluorescence method employed to detect DNA strand breaks. The staining results were investigated by flow cytometer. The preliminary results showed that more strand breaks occurred in cells hit by alpha particles with lower energies. Moreover, large TUNEL positive signals were obtained even with small percentages of cells irradiated and TUNEL signals were also obtained from non-targeted cells. These provided evidence for the bystander effect. 相似文献
47.
48.
49.
Jing Wang Walker D.M. Xiang Lu Majhi A. Kruseman B. Gronthoud G. Villagra L.E. van de Wiel P.J.A. Eichenberger S. 《Design & Test of Computers, IEEE》2007,24(3):226-234
Excessive power supply noise during test can cause overkill. This article discusses two models for supply noise in delay testing and their application to test compaction. The proposed noise models avoid complicated power network analysis, making them much faster than existing power noise analysis tools. can cause performance degradation and 相似文献
50.
碘量法测铜中物质性质和分析操作 总被引:3,自引:0,他引:3
本文讨论了碘量法测定铜量中一些有关物质的特性,以及这些性质对分析条件和操作的要求。 相似文献