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   78篇
  免费   6篇
化学工业   26篇
机械仪表   1篇
建筑科学   1篇
能源动力   2篇
轻工业   3篇
无线电   9篇
一般工业技术   20篇
冶金工业   15篇
自动化技术   7篇
  2021年   1篇
  2020年   3篇
  2019年   1篇
  2018年   2篇
  2017年   3篇
  2016年   1篇
  2015年   3篇
  2014年   3篇
  2013年   5篇
  2012年   4篇
  2011年   3篇
  2010年   4篇
  2009年   2篇
  2008年   5篇
  2007年   2篇
  2006年   7篇
  2005年   1篇
  2004年   4篇
  2003年   3篇
  2002年   4篇
  2001年   3篇
  2000年   2篇
  1999年   2篇
  1998年   1篇
  1997年   1篇
  1996年   2篇
  1995年   3篇
  1993年   2篇
  1992年   1篇
  1989年   1篇
  1987年   1篇
  1986年   1篇
  1984年   1篇
  1981年   1篇
  1979年   1篇
排序方式: 共有84条查询结果,搜索用时 15 毫秒
1.
2.
In this article, we present a systematic, controlled synthesis of water-dispersed, polymer-stabilized Au nanoparticles with different sizes by either self-reduction or ultraviolet (UV) irradiation-enhanced reduction in the presence of double hydrophilic block copolymers with different functional patterns. The morphology of the particles was found to be spherical, triangular, truncated triangular, and hexagonal under various conditions. In addition, both the particle size and shape could be controlled by variation of the functional group pattern of the block copolymers. With a hexacyclen functional block, we achieved a perfect match to the Au (111) face, resulting in extremely thin free-standing triangular and hexagonal nanoplatelets that show interference patterns in the electron beam due to deformations in the sub-Angstrom range. UV-visible spectra show that the plasmon absorption band can be fine tuned, depending on the type of the polymer and the irradiation power. The influence of the functional polymer groups and the irradiation on the formation of gold nanoparticles was investigated in more detail.  相似文献   
3.
4.
(E)-β-Chloro-α-phenylcinnamaldehyde and (E)- and (Z)-methyl α-tert-butoxycarbonyl-p-nitro-β-bromocinnamates in the presence of NCS ion in acetonitrile undergo an (E) ⇌ (Z) isomerization which is faster than the vinylic substitution. (E)- and (Z)-methyl α-cyano-β-mesyloxy- (and β-chloro-) p-nitrocinnamates undergo substitution under similar conditions without preceding isomerization. MO calculations gave the energy differences between the eclipsed and the perpendicular conformers of carbanions CH2CH2X and (NC)2ČH2X (X = Cl, NCS). These rotational barriers denote the hyperconjugation stabilization energy resulting from interaction of the C-X bond and the 2p(C) orbital. Both HCA values are high, those for X = Cl being 15–20% higher than for X = NCS. The limited literature data on the nucleofugality of NCS suggests that it can have a nucleofugality which is not much lower than that of Cl or Br. Consequently, NCS-catalyzed isomerizations of electrophilic vinyl chlorides and bromides, which involve a 180° internal rotation followed by a faster expulsion of NCS than of Cl from the initially formed intermediate carbanion Y'YC-C(R)(Cl)SCN, are not unreasonable, especially if solvation, which was not included in the calculations, plays an important role in the nucleofuge expulsion process.  相似文献   
5.
Survey data obtained from two independent samples of supervisors (Ns?=?68 and 109) supported the prediction that supervisors' experience of role conflict would correlate positively with their reported tendency to deliberately inflate subordinates' performance ratings. Contrary to expectation, in neither sample did supervisors' screening ability emerge as a moderator of the relation between role conflict and rating inflation. In a third independent sample of supervisors (N?=?25), in which rating inflation was operationalized on the basis of actual performance ratings of subordinates, strong support was obtained for both the predicted positive association between role conflict and rating inflation as well as the predicted moderating effect of screening ability on this relation. By contrast, the authors did not anticipate that supervisors' experience of role ambiguity would be directly associated with, or interact with screening ability to predict, rating inflation. The data from all three samples were, in general, in line with these expectations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
6.
Passive cooling systems use simple low-cost techniques to provide summer comfort in warm climates and can also be used to keep food, liquids and other materials at temperatures below ambient. Radiative cooling devices require a convective shield that should reject solar radiation but be transparent to mid-IR thermal radiation. In this paper, chemical solution deposition of thin semiconductor films (PbS and PbSe) onto polyethylene foils for radiative cooling applications is described. Optical and structural characterizations of the films were performed using UV–Vis, FTIR spectroscopies, X-ray diffraction and electron microscopy. Additionally, pigmented shields, which exhibit good radiation scattering properties, were prepared by incorporation of ZnS or ZnO into polyethylene. We also studied a combination of pigmented polyethylene foils coated with thin films of PbS that show improved optical properties for cooling purpose.  相似文献   
7.
Modeling the conductance and DNA blockade of solid-state nanopores   总被引:1,自引:0,他引:1  
We present measurements and theoretical modeling of the ionic conductance G of solid-state nanopores with 5-100 nm diameters, with and without DNA inserted into the pore. First, we show that it is essential to include access resistance to describe the conductance, in particular for larger pore diameters. We then present an exact solution for G of an hourglass-shaped pore, which agrees very well with our measurements without any adjustable parameters, and which is an improvement over the cylindrical approximation. Subsequently we discuss the conductance blockade ΔG due to the insertion of a DNA molecule into the pore, which we study experimentally as a function of pore diameter. We find that ΔG decreases with pore diameter, contrary to the predictions of earlier models that forecasted a constant ΔG. We compare three models for ΔG, all of which provide good agreement with our experimental data.  相似文献   
8.
This paper presents a package of FOTRAN IV subroutines for the out-of-core assembly and solution of a system of linear equations with a non-symmetric coefficient matrix, as met in many finite element applications. A skyline block storage mode is used for the coefficient matrix and a direct triangular decomposition method is employed to solve the system of linear equations. The block partitioning and storage mode of the coefficient matrix and the data transfer procedures for the assembly and solution of the system Ax = b are discussed in detail. Examples from the field of fluid dynamics are presented.  相似文献   
9.
Measurements of the hemodynamic parameters of the superior mesenteric artery were performed in 18 patients with celiac disease. Ten were studied at the time of diagnosis, when a small bowel biopsy showed a flat mucosa. The remaining eight patients were studied after complete clinical and histological recovery induced by a gluten-free diet. Doppler ultrasound flowmetry was used to measure blood flow in physiological and fasting conditions and after a mixed liquid test meal (Ensure-Plus). The results were compared with those of healthy subjects (N = 7). Mean basal flow was 50% higher in untreated celiac disease patients than in healthy controls and patients with chronic pancreatitis (P = NS). Postprandial mesenteric blood flow was significantly increased (P < 0.002) and delayed in time (P < 0.005) in celiac disease as compared to controls. Successful treatment reduced the mesenteric blood flow in celiac disease to normal values. Our study demonstrates that pathophysiological changes in the small bowel mucosa during the active clinical phase of celiac disease induce an abnormal splanchnic circulation.  相似文献   
10.
Valuable clinical and physiological data concerning the function of the cardiopulmonary system can be obtained from continuous monitoring of hemoglobin oxygen saturation (SaO2), oxygen tension (PO2), and carbon dioxide tension (PCO2) in blood. While periodic blood sampling is still used clinically to determine arterial blood gases, it is becoming apparent that the recent introduction of continuous noninvasive monitoring of blood gases can offer many advantages. This paper discusses the historical development and significant accomplishments of various techniques available for transcutaneous blood gas monitoring. Four major areas are reviewed: electrochemistry, spectrophotometry, mass spectrometry, and gas chromatography. For each of these techniques, the theoretical basis, instrumentation, and clinical applications are discussed.  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