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   107篇
  免费   2篇
  国内免费   7篇
化学工业   30篇
金属工艺   20篇
建筑科学   1篇
能源动力   2篇
轻工业   7篇
水利工程   1篇
石油天然气   5篇
无线电   4篇
一般工业技术   26篇
冶金工业   9篇
原子能技术   1篇
自动化技术   10篇
  2023年   1篇
  2021年   1篇
  2019年   5篇
  2018年   4篇
  2017年   4篇
  2016年   9篇
  2015年   2篇
  2014年   8篇
  2013年   7篇
  2012年   9篇
  2011年   17篇
  2010年   7篇
  2009年   8篇
  2008年   8篇
  2007年   2篇
  2006年   1篇
  2002年   2篇
  1997年   2篇
  1996年   2篇
  1989年   1篇
  1987年   3篇
  1985年   3篇
  1984年   4篇
  1982年   3篇
  1980年   1篇
  1979年   2篇
排序方式: 共有116条查询结果,搜索用时 15 毫秒
21.
In this study, the amorphous phase formation in Al80Fe10M10 (M = Ti, V, Ni) (at.%) ternary systems during mechanical alloying has been investigated. The milled samples were characterized using X-ray diffraction and differential thermal analyses. A thermodynamic analysis of the amorphous phase formation was performed for these systems using the Miedema model. The obtained results demonstrate that amorphous phases can be formed during the mechanical alloying process of the Al80Fe10M10 (M = Ti, V, Ni) ternary systems. The produced amorphous alloys exhibit one-stage crystallization during heating, which is amorphous to the Al13Fe4 intermetallic phases. The thermal stability of the produced amorphous phases decreases in the order of Al80Fe10Ti10 > Al80Fe10Ni10 > Al80Fe10V10.  相似文献   
22.
23.
BACKGROUND: The Commission on Cancer of the American College of Surgeons has called upon institutions providing cancer care to compare practice patterns and outcomes with the National Cancer Data Base (NCDB). Using data from the Virginia Mason Tumor Registry (VMTR), we sought to compare our pancreatic cancer care patterns with those reported nationally, while critically evaluating the accuracy and usefulness of our registry. METHODS: A review of the 906 computerized patient files in the VMTR from 1973 to 1995 was performed, with more detailed data on patients from the last 5 years retrieved from 224 manual abstracts. These data were compared with the 1991 NCDB for pancreatic cancer. RESULTS: The percent of cases according to AJCC stage in the NCDB (n = 9,715) versus the VMTR (n = 149), respectively, with cases of unknown stage excluded, were stage I 22% versus 22%, stage II 9% versus 12%, stage III 17% versus 28% (P <0.05) stage IV 52% versus 38% (P <0.05). One-third of the cases in the VMTR 1991 to 1995 were of unknown stage; number of cases with unknown stage for NCDB was 26.6%. The percent of surgical procedures for the NCDB (n = 7,802) versus the VMTR (n = 224), respectively, was pancreatectomy 14% versus 11%, local excision 1% versus 0%, no cancer-directed surgery 83% versus 89% (P <0.05), unknown 2% versus 0% (P <0.05). The actuarial relative survival rates for the 1991 NCDB versus 1987 to 1995 VMTR was 3-year 18% versus 38%, and 5-year 14% versus 35%. CONCLUSIONS: In comparison with the NCDB, VMTR may have fewer stage IV pancreatic cancers, but improvement is needed in decreasing the number of patients for whom the stage is unknown, as many of these likely represent late stage disease. We have a similar resection rate and a higher survival compared with the NCDB, but a mechanism is not in place to statistically compare our survival data with those of the NCDB. Even though all accredited hospitals are required to have a tumor registry, our data were difficult to compare with those of the NCDB because of coding and reporting deficiencies and inability to statistically compare survival data. Before our practice patterns and outcomes can be compared with national standards, both the VMTR and the NCDB must have standardized data collection and better access to the data.  相似文献   
24.
The Coulomb barrier is in general much higher than thermal energy. Nuclear fusion reactions occur only among few protons and nuclei (i.e., deuterium and tritium) with higher relative energies than Coulomb barrier. It is the equilibrium velocity distribution of these high-energy protons and nuclei that participates in determining the rate of nuclear fusion reactions. In the circumstance it is inappropriate to use the Maxwellian velocity distribution for calculating the nuclear fusion reaction rate. We use the relativistic equilibrium has a reduction factor with respect to that based on the Maxwellian distribution, which factor depends on the temperature, reduced mass and atomic numbers of the studied nuclear fusion reactions. In this paper, we concluded at energy range 105 (keV) ≤ E ≤ 106 (keV), that is smaller than reduced mass energy of deuterium–tritium, m r c 2, the numerical values of R and R M are not different from each other very much, but by increasing energy near the region of m r c 2 the difference between them are visible, also by increasing energy for example 9 × 106 (keV) ≤ E ≤ 10 × 106 (keV) the difference is obviously more visible. Therefore, we have to use relativistic equilibrium velocity distribution instead of Maxwellian velocity distribution.  相似文献   
25.
A comparison of the boundary element and superposition methods   总被引:16,自引:0,他引:16  
For some time now, the Boundary Integral Equation (BIE) Method or as it is alternately called the Boundary Element Method (BEM) has been hailed as the technique best suited to problems in elasticity and related fields, both for accuracy and efficiency. The authors demonstrate by example that this is not the case. A much simpler and more versatile technique, the Superposition Method (SUP), is introduced and is shown to outperform BEM in both areas. Followed by a discussion of the merits and drawbacks of each method, compact computer programs for both BEM and SUP and numerical results for nine different example problems are presented to support the authors' claim.  相似文献   
26.
The microstructure, thermal behavior, and mechanical properties of amorphous/nanocrystalline 70Fe-15Cr-4Mo-5P-4B-1C-1Si (wt.%) coatings produced by high velocity oxy fuel (HVOF) spraying of mechanically alloyed powders were investigated by x-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Thermal stability of samples was investigated using differential scanning calorimetry (DSC). The results show that by adjusting the HVOF parameters especially fuel/oxygen ratio and proper selection of powder composition, the desired microstructure with different amount of amorphous and nanocrystalline phases and therefore with different mechanical properties could be obtained.  相似文献   
27.
This work is an experimental study of the effects of nanoparticles with different characteristics and contents on foaming composites made of three different nanosilica particles with different geometrical and chemical surface properties in a polystyrene matrix. In addition to the general characteristics reported in our last study on the morphology of polymer–nanoparticle composites, this study shows that nanosilicas of larger sizes can result in foams of higher cell densities. Additionally, the cell densities of foams can be reduced if the nanoparticle surface becomes more affine to the polymer matrix chemically. These results show a correspondence with the effects of the characteristics of the nucleation agent on the nucleation of bubbles, which have been explored previously. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   
28.
An open-celled structure was produced using polystyrene and supercritical carbon dioxide in a novel batch process. The required processing conditions to achieve open-celled structures were predicted by a theoretical model and confirmed by the experimental data. The theoretical model predicts that at least a saturation pressure of 130 bar and a foaming time between 9 and 58 s are required for this system to produce an open-celled structure. The foaming temperature range has been selected to be higher than the polymer glass transition temperature yet not higher than a temperature limit where the gas starts leaving the system. The experimental results in the batch foaming process verified the model substantially. The SEM pictures showed the presence of pores between the cells, and the mercury porosimetry test results verified the overall open-celled structure. Experimental results also showed that by increasing the saturation pressure and the foaming temperature, there was a drop in the time required for open-celled structure formation. At saturation pressure of 130 bar, foaming temperature of 150 °C and a foaming time of 60 s, open-celled microcellular polystyrene foams were obtained using supercritical CO2 in the batch process. Based on the results, a schematic diagram, depicting the process of foam structure formation from nucleation to bubble coalescence and gas escape from polymer, was proposed. Theoretical calculations showed that by increasing foaming time, cell size was increased and cell density was reduced and the experimental results verified this prediction.  相似文献   
29.
A356/Al2O3 surface nanocomposite was produced by friction stir processing (FSP) method. X-ray diffractometery, optical and scanning electron microscopy, microhardness and nanoindentation tests were used to characterize the samples. The results indicated that the uniform distribution of Al2O3 particles in A356 matrix by FSP process can improve the mechanical properties of specimens. The hardness and elastic modulus of the as-received A356, the sample treated by the FSP without Al2O3 particles, surface micro- and nanocomposite specimens were about 75 Hv and 74 GPa, 69 Hv and 73 GPa, 90 Hv and 81 GPa, 110 Hv and 86 GPa, respectively.  相似文献   
30.
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