全文获取类型
收费全文 | 105篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
化学 | 17篇 |
晶体学 | 1篇 |
力学 | 38篇 |
综合类 | 1篇 |
数学 | 33篇 |
物理学 | 27篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 3篇 |
2013年 | 8篇 |
2012年 | 6篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2009年 | 8篇 |
2008年 | 4篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 1篇 |
2002年 | 10篇 |
2001年 | 3篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1992年 | 1篇 |
排序方式: 共有117条查询结果,搜索用时 15 毫秒
41.
42.
Luigi D'Agnillo J. B. P. Soares A. Penlidis 《Journal of Polymer Science.Polymer Physics》2002,40(10):905-921
The results of an interlaboratory or round‐robin experiment in high‐temperature gel permeation chromatography (HT‐GPC) analysis are presented. The intention was to determine and raise awareness of interlaboratory reproducibility of HT‐GPC techniques. Fifteen laboratories performed analyses of five polyethylene samples and standards SRM 1475 and 1476. Reproducibility, as measured by the interlaboratory standard deviation (sLAB), was greatly influenced by the breadth of the molecular weight distribution (MWD) and branching. The sLAB values for the weight‐average molecular weight (Mw) of linear polyethylenes of narrow and broad MWDs were 4 and 14%, respectively. For branched polymers, GPC viscometry methods are shown to measure significantly higher molecular weights than the noncoupled GPC method, with higher variance. For branched polyethylenes measured with GPC viscometry, the reproducibility of Mw was characterized by sLAB = 18%. Reproducibility of the SRM 1475 standard was better than for unknowns. The results for branched standard SRM 1476 emphasize the important role of the detection method in GPC but call into question the use of this material as a molecular weight standard. For single‐site polyethylene, only a handful of labs measured an MWD that closely matched the Flory distribution. Qualitatively, the responses indicate that many variations in instrument and analytical methods exist among laboratories; this is partly a reflection of the development and refinements that this technique must yet undergo before a truly standard method is widely accepted and practiced. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 905–921, 2002 相似文献
43.
Currently, several testing methods are under development to understand the resistance of polyethylene pipe materials to slow crack growth over comparably short time periods without using aggressive chemicals to accelerate the time to brittle failure. Strain hardening and crack round bar tests have recently been developed and published as ISO testing methods. However, a better understanding of these testing methods is still required with respect to the molecular parameters of the materials. Comparative studies with existing slow crack growth testing methods such as the notched pipe test are of significant interest to the industry. This study discusses correlations of molecular weight, molecular weight distribution, short chain branching and rheological properties of different polyethylene materials with their slow rack growth resistances obtained from the strain hardening and crack round bar tests and their correlations with notched pipe tests. 相似文献
44.
Gianni Caravaggio Chris Hebbern Luyi Ding Sabit Cakmak 《International journal of environmental analytical chemistry》2015,95(8):754-775
Thermal desorption gas chromatography mass spectrometry (TD-GC/MS) is becoming more commonly used for the quantification and identification of organic compounds in particulate matter (PM), including ambient and source PM such as diesel particulate matter (DPM). It has been proven as an alternative to the traditional solvent extraction (SE) method and liquid injection gas chromatograph mass spectrometry (LI-GC/MS). However, little information is available on how different types of TD-GC/MS systems compare to each other for analysis of real-world PM samples or to direct LI-GC/MS for analysis of PM components in a test solution. To address this, CanmetENERGY Characterization Laboratory initiated a round robin with the participation of 10 laboratories worldwide. Three sample types were analysed: (i) a test solution with a suite of pure compounds commonly found in PM, analysed by TD-GC/MS and LI-GC/MS; (ii) a DPM sample, analysed by TD-GC/MS and SE; and (iii) an ambient PM sample, analysed by TD-GC/MS. The first part of the study showed good overall performance and comparability between the different TD-GC/MS systems and LI-GC/MS method for the analysis of PM components in a test solution, with some variability of results due to system types and parameters used, concentration of calibration standards, and whether or not an internal standards was used. The analysis of the DPM sample showed greater variability between laboratories and methods as many PM components were present near the detection limit and matrix effects particularly affected the TD-GC/MS analysis of heavier n-alkanes. In the last part of the study, for the analysis of an ambient PM sample by TD-GC/MS, the analysis of variance showed good comparison between labs for polycyclic aromatic hydrocarbons (94% non-significant), but slightly lower for n-alkanes (68%) and biomarkers (57%). 相似文献
45.
基于不可压Navier-Stokes方程, 采用计算流体力学方法, 数值模拟与分析了层流圆管潜射流在密度均匀黏性流体中的演化机理及其表现特征, 定量研究了蘑菇形涡结构无量纲射流长度L*、螺旋型涡环半径R*及其包络外形长度d*等几 何特征参数随无量纲时间t*的变化规律. 数值结果表明, 蘑菇形涡结构的形成与演化过程可分为三个不同的阶段: 启动阶段、发展阶段和衰退阶段. 在启动阶段, L*和d*随t* 线性变化, 而R*则近似为一个常数; 在发展阶段, 蘑菇形涡结构的演化具有自相似性, L*, R*和d*与t*1/2均为同一正比关系, 而且雷诺数和无量纲射流时间不影响该正比关系; 在衰退阶段, L* 和R* 正比于t*1/5, 而d*则近似为一个常数. 此外, 还对蘑菇形涡结构二次回流点、 动量源作用中心及其几何中心的速度变化规律、垂向涡量分布特征和 涡量-流函数关系进行了分析.
关键词:
圆管潜射流
蘑菇形涡结构
演化机理 相似文献
46.
47.
利用溢流恒压装置产生具有稳定出流速度的层流圆管潜射流,结合染色液流态显示方法,在多种射流时间和雷诺数组合下,实验研究了该射流动量在密度均匀黏性流体中的演化机理及其表现特征,定量分析了蘑菇型涡结构的无量纲射流长度L*、螺旋型涡环半径R*及其包络外形长度d*等几何特征参数随无量纲时间t*的变化规律。系列实验结果表明,蘑菇型涡结构的形成与演化过程可分为3个不同的阶段,分别为启动阶段、发展阶段和衰退阶段。在启动阶段,L*和d*随t*线性变化,而R*则近似为一个常数。在发展阶段,蘑菇型涡结构的演化具有自相似性,在各种射流时间和雷诺数组合下,L*,R*和d*与t*1/2均为同一正比关系,而且实验结果与基于斯托克斯(Stokes)近似的理论解结果一致。在衰退阶段,蘑菇型涡结构会发生两类形式的演化,第1类衰退出现在射流结束之后,其间L*和R*与t*1/5相关,而d*近似为一个常数;第2类衰退出现在射流结束之前,当射流动量达到某个临界值后,蘑菇型涡结构就会发生破碎等现象。 相似文献
48.
49.
In a previous paper, we had proved that the permutation group generated by the round functions of an AES-like cipher is primitive.
Here we apply the O’Nan Scott classification of primitive groups to prove that this group is the alternating group.
相似文献
50.
本文研究雷诺数(Re)对圆形渐缩喷嘴湍流射流的影响.实验在射流出口雷诺数为 Re = 4050—20100 的范围内进行,分别测量了射流出口、中心线的平均及湍流流场以及部分径向剖面速度分布.所有测量均采用单热线恒温热线风速仪进行高频采样,所测流场范围在轴向上为 0—30d(这里d为射流出口直径).虽然出口速度分布均为"平顶帽"形,但测量结果依然反映出Re对射流出口以及下游流场有强烈的影响.当Re小于临界值(~10000)时
关键词:
雷诺数
圆形射流
热线风速仪 相似文献