首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   144篇
  免费   3篇
化学工业   14篇
机械仪表   2篇
建筑科学   7篇
轻工业   5篇
无线电   67篇
一般工业技术   15篇
冶金工业   31篇
原子能技术   2篇
自动化技术   4篇
  2022年   1篇
  2021年   1篇
  2019年   1篇
  2018年   3篇
  2017年   3篇
  2016年   3篇
  2014年   7篇
  2013年   7篇
  2012年   5篇
  2011年   7篇
  2010年   6篇
  2009年   3篇
  2008年   9篇
  2007年   6篇
  2006年   7篇
  2005年   8篇
  2004年   4篇
  2003年   5篇
  2002年   3篇
  2001年   3篇
  1999年   1篇
  1998年   11篇
  1997年   4篇
  1996年   2篇
  1995年   7篇
  1994年   3篇
  1993年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1983年   3篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1976年   2篇
  1973年   1篇
  1972年   1篇
  1960年   1篇
  1959年   2篇
  1958年   1篇
  1937年   1篇
排序方式: 共有147条查询结果,搜索用时 62 毫秒
1.
Donor−acceptor cyclopropanes are convenient precursors to reactive and versatile 1,3-dipoles, and have found application in the synthesis of a variety of carbo- and heterocyclic scaffolds. This perspective review details our laboratory's use of donor−acceptor cyclopropanes as intermediates toward the total synthesis of various natural products. We also discuss our work in the development of novel cycloadditions and rearrangements of donor−acceptor cyclopropanes and aziridines, as well as an example of an aryne insertion proceeding via fragmentation of a transient donor−acceptor cyclobutane.  相似文献   
2.
Inductively coupled plasma (ICP) using hydrogen-based gas chemistry has been developed to meet requirements for deep HgCdTe mesa etching and shallow CdTe passivation etching in large format HgCdTe infrared focal plane array (FPA) fabrication. Large format 2048×2048, 20-μm unit-cell short wavelength infrared (SWIR) and 2560×512, 25-μm unit-cell midwavelength infrared (MWIR) double-layer heterojunction (DLHJ) p-on-n HgCdTe FPAs fabricated using ICP processing exhibit >99% pixel operability. The HgCdTe FPAs are grown by molecular beam epitaxy (MBE) on Si substrates with suitable buffer layers. Midwavelength infrared detectors fabricated from 4-in. MBE-grown HgCdTe/Si substrates using ICP for mesa delineation and CdTe passivation etching demonstrate measured spectral characteristics, RoA product, and quantum efficiency comparable to detectors fabricated using wet chemical processes. Mechanical samples prepared to examine physical characteristics of ICP reveal plasma with high energy and low ion angle distribution, which is necessary for fine definition, high-aspect ratio mesa etching with accurate replication of photolithographic mask dimensions.  相似文献   
3.
State-of-the-art (112)B CdZnTe substrates were examined for near-surface tellurium precipitate-related defects. The Te precipitate density was observed to be fairly uniform throughout the bulk of the wafer, including the near-surface region. After a molecular beam epitaxy (MBE) preparation etch, exposed Te precipitates, small pits, and bumps on the (112)B surface of the CdZnTe wafer were observed. From near-infrared and dark field microscopy, the bumps and small pits on the CdZnTe surface are associated with strings of Te precipitates. Raised bumps are Te precipitates near the surface of the (112)B CdZnTe where the MBE preparation etch has not yet exposed the Te precipitate(s). An exposed Te precipitate sticking above the etched CdZnTe surface plane occurs when the MBE preparation etch rapidly undercuts a Te precipitate. Shallow surface pits are formed when the Te precipitate is completely undercut from the surrounding (112)B surface plane. The Te precipitate that was previously located at the center of the pit is liberated by the MBE preparation etch process.  相似文献   
4.
Morphology of Inductively Coupled Plasma Processed HgCdTe Surfaces   总被引:1,自引:0,他引:1  
Inductively coupled plasma (ICP) processing has become the industrial processing standard for HgCdTe and its related II–VI compounds. In this study ICP processes were developed that allow several microns of HgCdTe to be plasma etched while maintaining a low root-mean-square (RMS) roughness, and even improving the surface roughness in the case of HgCdTe-on-Si. These ICP processes are superior to older electron cyclotron resonance (ECR) plasma etches. The resulting ICP plasma processed surfaces are oxygen and carbon free, have a good reflection high-energy electron diffraction (RHEED) pattern, and have only a small amount of mercury depletion, x = 0.22 to 0.47 (where x is the ratio of Cd to␣Hg), in the first 25 ? to 30 ? of the HgCdTe. Nanofeatures of the as-grown HgCdTe are retained during the process and are believed to be indicative of the fundamental defect mechanisms in the different HgCdTe etched surfaces. Results from these experiments strongly suggest that ICP plasma processes can be used to delineate pixels, etch vias, clean surfaces, and even produce epi-ready surfaces that would allow HgCdTe to become much more manufacturable, and perhaps allow the replacement of wet processing in HgCdTe.  相似文献   
5.
6.
The present review paper supports the approach to deliver melatonin and to target melatonin receptors for neuroprotection in stroke. We discuss laboratory evidence demonstrating neuroprotective effects of exogenous melatonin treatment and transplantation of melatonin-secreting cells in stroke. In addition, we describe a novel mechanism of action underlying the therapeutic benefits of stem cell therapy in stroke, implicating the role of melatonin receptors. As we envision the clinical entry of melatonin-based therapeutics, we discuss translational experiments that warrant consideration to reveal an optimal melatonin treatment strategy that is safe and effective for human application.  相似文献   
7.
High-performance 20-μm unit-cell two-color detectors using an n-p+-n HgCdTe triple-layer heterojunction (TLHJ) device architecture grown by molecular beam epitaxy (MBE) on (211)-oriented CdZnTe substrates with midwavelength (MW) infrared and long wavelength (LW) infrared spectral bands have been demonstrated. Detectors with nominal MW and LW cut-off wavelengths of 5.5 μm and 10.5 μm, respectively, exhibit 78 K LW performance with >70 % quantum efficiency, reverse bias dark currents below 300 pA, and RA products (zero field of view, 150-mV bias) in excess of 1×103 Ωcm2. Temperature-dependent current-voltage (I–V) detector measurements show diffusion-limited LW dark current performance extending to temperatures below 70 K with good operating bias stability (150 mV ± 50 mV). These results reflect the successful implementation of MBE-grown TLHJ detector designs and the introduction of advanced photolithography techniques with inductively coupled plasma (ICP) etching to achieve high aspect ratio mesa delineation of individual detector elements with benefits to detector performance. These detector improvements complement the development of high operability large format 640×480 and 1280×720 two-color HgCdTe infrared focal plane arrays (FPAs) to support third generation forward looking infrared (FLIR) systems.  相似文献   
8.
The activation of nuclear factor (NF)-kappaB by 12(R)-hydroxyeicosatrienoic acid [12(R)-HETrE], an arachidonic acid metabolite with potent stereospecific proinflammatory and angiogenic properties, was examined and its role in the angiogenic response was determined in capillary endothelial cells derived from coronary microvessels. Electrophoretic mobility-shift assay of nuclear protein extracts from cells treated with 12(R)-HETrE demonstrated a rapid and stereospecific time- and concentration-dependent increase in the binding activity of NF-kappaB, which was inhibitable by the antioxidants N-acetylcysteine, butylated hydroxyanisole, and pyrrolidine dithiocarbamate and was partially attenuated by the protein kinase C inhibitors, staurosporine and calphostin C. Neither 12(S)-HETrE nor other related eicosanoids--e.g., 12(R)-HETE, 12(S)-HETE, and leukotriene B4--stimulated the activation of NF-kappaB relative to 12(R)-HETrE, substantiating the claim for a specific receptor-mediated mechanism. 12(R)-HETrE stimulated the formation of capillary-like cords of microvessel endothelial cells distinguishable from a control; this effect was comparable to that observed with basic fibroblast growth factor (bFGF). Inhibition of NF-kappaB activation resulted in inhibition of capillary-like formation of endothelial cells treated with 12(R)-HETrE by 80% but did not affect growth observed with bFGF. It is suggested that 12(R)-HETrE's angiogenic activity involves the activation of NF-kappaB, possibly via protein kinase C stimulation and the generation of reactive oxygen intermediates for downstream signaling.  相似文献   
9.
The effect of nitrogen content on stacking fault energy (SFE) has been measured in a series of Fe-21Cr-6Ni-9Mn alloys. Stacking fault energies were determined from node measurements using weak beam imaging techniques in transmission electron microscopy. Nitrogen additions lower the SFE from 53 mJ/m2 at 0.21 wt pct to 33 mJ/m2 at 0.24 wt pct. Further increases to 0.52 wt pct do not markedly change the SFE. Carbon and silicon had no effect on SFE in the ranges 0.010 to 0.060 wt pct C and 0.17 to 0.25 wt pct Si. The shift in SFE from 0.21 to 0.24 wt pct N is accompanied by a transition to a more planar plastic deformation mode. The sharp transition precludes the use of linear regression analysis for relating SFE to nitrogen content in this class of alloys.  相似文献   
10.
In order to investigate the three-dimensional (3-D) mechanical properties of blood vessels, a new experimental device is described allowing in vitro static and dynamic measurements on segments of arteries with high technical performances. Static tests are applied to sheep common carotid arteries. Considering a thick-walled cylindrical model of orthotropic material under large deformations, a classical 3-D approach based on strain energy density is used to calculate the resulting mechanical behavior law in radial and circumferencial directions and stresses distribution throughout the wall thickness. Results are presented with reference to unloaded and zero-stress initial state thanks to simple measurements of inner and outer circumferences. A particular ratio relating the two main stresses (circumferential and longitudinal) is calculated that put into the forth the progressive modifications in the direction of the predominant stress in the wall and the specific radial location where these changes occur. The authors observe that this point location is a function of the test conditions of the specimen, i.e., stretching length and level of pressure  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号