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排序方式: 共有81条查询结果,搜索用时 31 毫秒
1.
本文综合评述了近年来2-[2-(二环己膦基)苯基]-1-甲基-1H-吲哚(CM-Phos)膦配体及其衍生物在钯催化的交叉偶联反应中的应用, 主要根据不同种类的交叉偶联反应进行系统性分述, 并对该领域的发展前景进行了展望. 相似文献
2.
High-resolution MR venography of cerebral arteriovenous malformations 总被引:20,自引:0,他引:20
Essig M Reichenbach JR Schad LR Schoenberg SO Debus J Kaiser WA 《Magnetic resonance imaging》1999,17(10):1050-1425
The purpose of this study was to evaluate the diagnostic potential of a high-resolution magnetic resonance (MR) venography technique in patients with cerebral arteriovenous malformations (AVMs). A high-resolution 3D gradient echo sequence was used with a long echo time TE to obtain venous information down to sub-pixel sized vessel diameters of several hundred microns. The method is based on the paramagnetic property of deoxyhemoglobin, and the resulting developing phase difference between veins and brain parenchyma at long echo times which leads to signal cancellation. The reconstructed venograms were compared with time-of-flight (TOF)-MR angiography using qualitative and quantitative criteria with the conventional digital subtraction angiography serving as the reference gold standard. In 17 patients with angiographically proven cerebral AVMs, the method indicates its potential in clinical applications. Venography was able to detect all AVMs whereas TOF-MRA failed in three patients. In the delineation of venous drainage patterns MR venography was superior to TOF-MRA, however, the method failed in the detection of about half of the main feeding arteries, as expected. Due to susceptibility artifacts at air/tissue boundaries and interference with paramagnetic hemosiderin, venography was limited with respect to the delineation of the exact nidus sizes and shapes in ten patients with AVMs located close to the skull base or having suffered from previous bleeding. Although the visualization of draining veins represents an important prerequisite in the surgical and radiosurgical treatment planning of cerebral AVMs, application of high resolution MR venography may be limited in the diagnostic work-up in some of these patients. On the other hand, it may be of special importance in the early detection and assessment of small AVMs that are difficult to diagnose with other MR methods. 相似文献
3.
I. J. Schoenberg 《Israel Journal of Mathematics》1971,10(3):261-274
Letx
v
=cos (πν/n) (v=0, 1, …,n). It is shown that theB-splineM(x)=M(x; x
0
,x
1
,…, x
n
) is such thatM
n
(n)
(x) has a constant absolute value (=2
n−2 (n−1)!) in [−1, 1]. Its integralf
0(x)=∫
−1
x
M(t)dt is shown to have an optimal property that allows to solveexplicitly a certain time-optimal control problem. 相似文献
4.
Disappearance of tumor contrast on contrast-enhanced FLAIR imaging of cerebral gliomas 总被引:6,自引:0,他引:6
Contrast-enhanced fluid-attentuated inversion recovery (FLAIR) magnetic resonance (MR) imaging has shown to be a valuable diagnostic modality in the assessment of cerebral gliomas. In this study we report of a potential pitfall regarding the delineation of enhancing tumor parts on contrast enhanced FLAIR imaging. In a limited number of patients, the administration of gadolinium obscures the area of contrast enhancement on contrast enhanced FLAIR images. Therefore the delineation of the macroscopic tumor parts, which are of great importance for the treatment planning is substantially worsened. 相似文献
5.
I. J. Schoenberg 《Mathematische Zeitschrift》1934,38(1):546-564
Ohne Zusammenfassung 相似文献
6.
Isac Schoenberg 《Mathematische Zeitschrift》1930,32(1):321-328
Ohne Zusammenfassung 相似文献
7.
Frederic Paik Schoenberg 《Annals of the Institute of Statistical Mathematics》2002,54(2):445-457
The process obtained by rescaling a homogeneous Poisson process by the maximum likelihood estimate of its intensity is shown to have surprisingly strong self-correcting behavior. Formulas for the conditional intensity and moments of the rescaled Poisson process are derived, and its behavior is demonstrated using simulations. Relationships to the Brownian bridge are explored, and implications for point process residual analysis are discussed. 相似文献
8.
Schoenberg K.F. Gerwin R.A. Henins I. Mayo R.M. Scheuer J.T. Wurden G.A. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(6):625-644
Preliminary experimental and theoretical research that was directed toward the study of quasi-steady-state power flow in a large, unoptimized, multimegawatt coaxial plasma thruster is summarized. Large coaxial thruster operation is discussed, and the experimental results are evaluated and interpreted with a view to the development of efficient, steady-state, megawatt-class magnetoplasmadynamic (MPD) thrusters 相似文献
9.
Frederic Paik Schoenberg 《Annals of the Institute of Statistical Mathematics》2006,58(2):223-233
Simple point processes are often characterized by their associated compensators or conditional intensities. Non-simple point
processes are not uniquely determined by their conditional intensity and compensator, so instead one may identify with the
point process its associated simple point process and corresponding conditional intensity, on an expanded mark space. Some
relations between the conditional intensity on the expanded mark space and the ordinary conditional intensity are investigated
here, and some classes of separable non-simple processes are presented. Transformations into simple point processes, involving
thinning and rescaling, are presented. 相似文献