全文获取类型
收费全文 | 781篇 |
免费 | 47篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 139篇 |
金属工艺 | 19篇 |
机械仪表 | 54篇 |
建筑科学 | 38篇 |
矿业工程 | 7篇 |
能源动力 | 21篇 |
轻工业 | 71篇 |
水利工程 | 5篇 |
无线电 | 96篇 |
一般工业技术 | 179篇 |
冶金工业 | 89篇 |
原子能技术 | 2篇 |
自动化技术 | 101篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 31篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 16篇 |
2017年 | 22篇 |
2016年 | 21篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 48篇 |
2012年 | 55篇 |
2011年 | 71篇 |
2010年 | 43篇 |
2009年 | 53篇 |
2008年 | 27篇 |
2007年 | 39篇 |
2006年 | 27篇 |
2005年 | 20篇 |
2004年 | 25篇 |
2003年 | 26篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 20篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 19篇 |
1995年 | 22篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1973年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有831条查询结果,搜索用时 15 毫秒
1.
Woo‐Seok Cheong 《ETRI Journal》2003,25(6):503-509
Selective epitaxial growth (SEG) of silicon has attracted considerable attention for its good electrical properties and advantages in building microstructures in high‐density devices. However, SEG problems, such as an unclear process window, selectivity loss, and nonuniformity have often made application difficult. In our study, we derived processing diagrams for SEG from thermodynamics on gas‐phase reactions so that we could predict the SEG process zone for low pressure chemical vapor deposition. In addition, with the help of both the concept of the effective supersaturation ratio and three kinds of E‐beam patterns, we evaluated and controlled selectivity loss and nonuniformity in SEG, which is affected by the loading effect. To optimize the SEG process, we propose two practical methods: One deals with cleaning the wafer, and the other involves inserting dummy active patterns into the wide insulator to prevent the silicon from nucleating. 相似文献
2.
Norton NBD 200 silicon nitride ceramics were implanted with sodium to a dose of 7.0×1015cm-2 at 72 keV (1 at% peak sodium content at 100 nm). The sodium-implanted samples were further implanted with aluminium to 7.3×1015cm-2 at 87 keV (1 at% peak aluminium content at 100 nm). The implanted and unimplanted samples were oxidized in 1 atm dry oxygen
at 1100 and 1300°C for 2–6 h. Profilometry and scanning electron microscopy measurements indicated that sodium implantation
led to up to a two-fold increase in the oxidation rate of silicon nitride. The sodium effect was effectively neutralized when
aluminium was co-implanted. The opposite effects of sodium and aluminium on the oxidation resistance of silicon nitride can
be attributed to their different roles in modifying the structure and properties of the oxide formed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
3.
4.
Rh/Lil/SnR4 is an effective catalyst system for the conversion of methyl formate to acetic acid under carbon monoxide pressure. The effects
of solvent and initial CO partial pressure on the turnover rate of the reaction were investigated. The possibility of replacing
some of the iodide promoters by tin compounds has been probed. 相似文献
5.
Temporal order and functional analysis of mutations within the Fli-1 and p53 genes during the erythroleukemias induced by F-MuLV 总被引:1,自引:0,他引:1
JC Howard S Yousefi G Cheong A Bernstein Y Ben-David 《Canadian Metallurgical Quarterly》1993,8(10):2721-2729
The erythroleukemias induced by Friend murine leukemia virus (F-MuLV) result from the accumulation of a number of genetic changes, including activation of the Fli-1 proto-oncogene and inactivation of the p53 tumor suppressor gene. We have determined the temporal order of mutation of the genes involved in this multistage malignancy, by serial in vivo transplantation of F-MuLV induced primary erythroleukemias into syngenic Balb/c mice. These primary tumors are capable of growing when transplanted into syngenic mice, but die after several days of in vitro culture. From the transplanted tumors grown in syngenic mice, erythropoietin-dependent cell lines were established in culture that are clonally related to cells in the primary tumors. We show that retroviral insertional activation of the Fli-1 ets family member is the first detectable genetic event in F-MuLV induced primary erythroleukemias. Mutations in the p53 gene were observed in the Epo-dependent cell lines but not in the transplanted erythroleukemias used to establish these cell lines in culture. These data suggest that activation of Fli-1 plays an important role in the early stages of F-MuLV-induced leukemia, perhaps by altering the self-renewal probabilities of erythroid progenitor cells and that p53 mutations immortalize these cells, enabling them to grow in vitro in the presence of Epo. 相似文献
6.
7.
K. Lefmann B. Lake G. Aeppli S.-W. Cheong N. B. Christensen K. N. Clausen S. Hayden T. E. Mason D.F. McMorrow H. A. Mook H. M. Rønnow H. Takagi 《Journal of Low Temperature Physics》2004,135(5-6):621-664
One important area of modern condensed matter research is the investigation of the nature of the superconducting cuprates. Much progress in this field has been obtained with the technique of neutron scattering. We here present a review of neutron scattering studies of the high-temperature superconductor La2?xSrxCuO4, performed at Risø National Laboratory. We review the work on the mapping of the incommensurate spin fluctuations, the investigation of the gap in the fluctuation spectrum, the magnetic properties of the vortices appearing in an applied field, and the quantum critical behaviour of the system. We discuss our findings in the light of results of neutron scattering from other groups, on other cuprate systems, and results from other experimental methods, e.g. NMR, μSR, STM, X-ray diffraction, and ARPES. We end with a discussion on the implications of the experimental results for the progress in the general understanding of high-temperature superconductivity. PACS numbers: 61.12.Ex, 74.20.Mn, 74.72.Dn, 75.25.+z, 78.70.Nx. 相似文献
8.
In this paper, mobility parameters for enhancement-mode N-channel 4H SiC MOSFETs are extracted and implemented into 2-D device simulation program and SPICE circuit simulator. The experimental data were obtained from lateral N-channel 4H SiC MOSFETs with nitrided oxide–semiconductor interfaces, exhibiting normal mobility behavior. The presence of increasing interface-trap density (Dit) toward the edge of the conduction band is included during the 2-D device simulation. Using measured distribution of interface-trap density for simulation of the transfer characteristics leads to a good agreement with the experimental transfer characteristic. 相似文献
9.
Limited past studies have indicated that Si3 N4 doped with Sc2 O3 may exhibit high-temperature mechanical properties superior to Si3 N4 systems with various other oxide sintering additives. High-temperature deformation of this system was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, Sc and O, exist in small amounts at thin grain boundary layers and within secondary phases at triple and multiple grain boundary junctions. The secondary phase is devitrified as crystalline Sc2 Si2 O7 . Deformation of the samples was dominated by cavitation rather than dislocation processes. Thus, the excellent deformation resistance of the samples at high temperature can be attributed to the high refractories and enhanced crystallization of a secondary phase. 相似文献
10.
The effects of dopant (Ga) concentration, post-heat treatment temperatures, and different heat treatment environments on the morphology, electrical and optical properties of ZnO films were studied. ZnO films doped with Ga are derived from non-alkoxide zinc acetate via the alcoholic route by a sol–gel dip-coating technique. Introduction of Ga, as a dopant, can reduce crystallite size, which is attributed to the increased number of nucleation centers. Grain growth was also observed at high post-heat treatment temperature. It was discovered that different post-heat treatment environments (air or reduced atmosphere) did not change the structure orientation, microstructure shapes and size. It was found that the sheet resistance, Rs could be reduced by an order of magnitude, using post-heat treatment in reduced atmosphere (4%H2–96%N2). 相似文献