全文获取类型
收费全文 | 1448篇 |
免费 | 29篇 |
国内免费 | 1篇 |
专业分类
化学 | 1084篇 |
晶体学 | 4篇 |
力学 | 22篇 |
数学 | 205篇 |
物理学 | 163篇 |
出版年
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 18篇 |
2018年 | 11篇 |
2016年 | 25篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 41篇 |
2012年 | 54篇 |
2011年 | 47篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 55篇 |
2007年 | 56篇 |
2006年 | 45篇 |
2005年 | 39篇 |
2004年 | 36篇 |
2003年 | 31篇 |
2002年 | 43篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 16篇 |
1998年 | 14篇 |
1997年 | 22篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 23篇 |
1993年 | 17篇 |
1992年 | 12篇 |
1991年 | 21篇 |
1990年 | 23篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 20篇 |
1986年 | 27篇 |
1985年 | 31篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 27篇 |
1981年 | 31篇 |
1980年 | 30篇 |
1979年 | 25篇 |
1978年 | 25篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1968年 | 10篇 |
1966年 | 10篇 |
1965年 | 13篇 |
1961年 | 10篇 |
排序方式: 共有1478条查询结果,搜索用时 640 毫秒
81.
Detection of myocardial viability by low-dose dobutamine Cine MR imaging 总被引:15,自引:0,他引:15
Sandstede JJ Bertsch G Beer M Kenn W Werner E Pabst T Lipke C Kretschmer S Neubauer S Hahn D 《Magnetic resonance imaging》1999,17(10):614-1443
The purpose of this work was to test the diagnostic value of dobutamine stress magnetic resonance imaging (MRI) for predicting recovery of regional myocardial contractility after revascularization. Cardiac wall motion abnormalities are due to either non-viable and/or scarred, or viable, but hibernating, myocardial tissue. Dobutamine stress leads to increased systolic wall thickening only in viable myocardium. Twenty-five patients with akinetic or dyskinetic myocardial regions were examined with a Cine FLASH-2D sequence at rest and during dobutamine stress (10 μg/kg/min). Patients were re-examined at rest 3, and in case of persisting wall motion defects, 6 months after revascularization. Criterion of viability was increasing end-systolic wall thickening during stress and/or at follow-up. Akinetic regions related either to the LAD (n = 19) or to the RCA (n = 6) were judged viable if >=50% of the affected segments improved. MR studies were completed in all subjects without arrhythmia or need for early terminations due to symptoms. Sensitivity, specificity, and positive predictive value for the prediction of myocardial viability were 61%, 90%, and 87% for the segment-related analysis, and 76%, 100%, and 100% for the patient-related analysis based on coronary artery distribution, respectively. Dobutamine stress MRI allows to predict global functional recovery of akinetic myocardial regions after revascularization with a high positive predictive value and high specificity. 相似文献
82.
83.
84.
85.
86.
Emanuel Vogel Hans-Wilhelm Engels Saichi Matsumoto Johann Lex 《Tetrahedron letters》1982,23(17):1797-1800
An expedient new synthesis of benzo[c]octalene starting from the Diels-Alder adduct of benzocyclobutadiene to 7,8-dimethylenecycloocta-1,3,5-triene is described. This octalene derivative, in solution, exists as an equilibrating mixture of the double bond isomers (2) and (3) whereas in its crystalline state only the isomer (2) is present. 相似文献
87.
88.
Summary In a recent paper [11], two of the authors investigated a fast reduction method for solving difference equations which approximate certain boundary value problems for Poisson's equation. In this second paper, we prove the numerical stability of the reduction method, and also report on further developments of the method. For the general case, the provided bounds for the numerical errors behave roughly like the condition numberO(n
2) of the linear system; for more realistic model problems estimates of order less thanO(n) are obtained (n
–1=h=mesh width). The number of operations required for the reduction method isO(n
2
), for the usual five-point difference formula, as well as for the common nine-point formula with discretization error of orderh
4. 相似文献
89.
The relation between sample mass andDSC-amplitude was investigated under various experimental conditions for vitreous quartz, both as discs and powders. Contrary to other authors3 proportionality has been found up to the highest masses (75 mg) used. A statistical analysis of the data indicates that the accuracy of directC p-measurements byDSC can be increased by determining the blank value by extrapolation of the amplitudes for several masses to zero mass instead of using the usual procedure, which involves a run with the empty pans. The overall error ofC p due to instrument errors is estimated not to exceed 2%. 相似文献
90.