全文获取类型
收费全文 | 1319篇 |
免费 | 21篇 |
国内免费 | 3篇 |
专业分类
化学 | 682篇 |
晶体学 | 33篇 |
力学 | 34篇 |
数学 | 201篇 |
物理学 | 393篇 |
出版年
2020年 | 14篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 93篇 |
2012年 | 59篇 |
2011年 | 58篇 |
2010年 | 30篇 |
2009年 | 16篇 |
2008年 | 62篇 |
2007年 | 50篇 |
2006年 | 68篇 |
2005年 | 60篇 |
2004年 | 56篇 |
2003年 | 30篇 |
2002年 | 40篇 |
2001年 | 32篇 |
2000年 | 26篇 |
1999年 | 24篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 25篇 |
1995年 | 25篇 |
1994年 | 22篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 12篇 |
1987年 | 19篇 |
1986年 | 28篇 |
1985年 | 26篇 |
1984年 | 10篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 15篇 |
1977年 | 24篇 |
1976年 | 24篇 |
1975年 | 24篇 |
1974年 | 12篇 |
1973年 | 7篇 |
1971年 | 7篇 |
1970年 | 11篇 |
排序方式: 共有1343条查询结果,搜索用时 546 毫秒
991.
992.
993.
N. A. B. Gray James G. Nourse Christopher W. Crandell Dennis H. Smith Carl Djerassi 《Magnetic resonance in chemistry : MRC》1981,15(4):375-389
Computer programs for encoding canonical representations of stereochemical substructural environments are presented. Applications of these substructure codes in the study of relationships between molecular structure and chemical shifts observed in 13C NMR spectra are described, using natural products as examples. The utility of the codes for the detection of erroneous spectral assignment is illustrated. 相似文献
994.
995.
Gray Malcolm B. McCLELLAND David E. Barton Mark Kawamura Seiji 《Optical and Quantum Electronics》1999,31(5-7):571-582
A small Michelson interferometer has been configured as a tracking mirror displacement sensor in order to achieve both large dynamic range (2.1 mm) and excellent sensitivity
across a broad frequency range (6Hz–3 kHz). The interferometer is illuminated by a simple LED, uses broadband, non-polarising beamsplitters and contains no lensing optics. A DC-coupled balanced detector provides an error signal that is used to position the tracking mirror of the Michelson interferometer so as to maintain an interferometer operating position close to the centre of a particular fringe. The total interferometric sensor provides a small, simple and cost-effective means of achieving high-resolution displacement measurements. 相似文献
996.
Although the mechanisms of fibrillation are no doubt multi-faceted, the geometry of the heart may play a major role in the dynamics of wave propagation during fibrillation [A. T. Winfree, Science 266, 1003-1006 (1994)]. The ventricles are thick chambers made up of sheets of parallel muscle fibers with the direction of fibers rotating across the ventricular walls (rotational anisotropy). The thick walls of the ventricles allow reentry to develop transmurally, provided the wavelength is sufficiently small. Depending on the kinetics of heart cells, the dynamics of rotating waves in three dimensions may be fundamentally different than in two dimensions, leading to destabilization of reentry and ventricular fibrillation (VF) in thick ventricles. The atria have an intricate geometry comprised of a thin sheet of cardiac tissue attached to a very complex network of pectinate muscles. The branching geometry of the pectinate muscles may lead to destabilization of two-dimensional reentry via "long-distance" electrical connections giving rise to atrial fibrillation (AF). Therefore, although fibrillation occurs via complex three-dimensional wave propagation in the ventricles and the atria, the underlying mechanisms and factors that sustain VF and AF are probably different.(c) 1998 American Institute of Physics. 相似文献
997.
This article reviews recent data supporting the conjecture that, in the structurally and electrophysiologically normal heart, cardiac fibrillation is not a totally random phenomenon. Experimental and numerical studies based on the theory of excitable media suggest that fibrillation in the mammalian ventricles is the result of self-organized three-dimensional (3-D) electrical rotors giving rise to scroll waves that move continuously (i.e., drift) throughout the heart at varying speeds. A brief review of studies on the dynamics of rotors in two-dimensional (2-D) and 3-D excitable media is presented with emphasis on the experimental demonstration of such dynamics in cardiac muscle of various species. The discussion is centered on rotor dynamics in the presence and the absence of structural heterogeneities, and in the phenomena of drifting and anchoring, which in the electrocardiogram (ECG) may manifest as life-threatening cardiac rhythm disturbances. For instance, in the rabbit heart, a single electrical rotor that drifts rapidly throughout the ventricles gives rise to complex patterns of excitation. In the ECG such patterns are indistinguishable from ventricular fibrillation. On the other hand, a rotor that anchors to a discontinuity or defect in the muscle (e.g., a scar, a large artery or a bundle of connective tissue) may result in stationary rotating activity, which in the ECG is manifested as a form of so-called "monomorphic" ventricular tachycardia. More recent data show that ventricular fibrillation occurs in mammals irrespective of size or species. While in small hearts, such as those of mice and rabbits, a single drifting or meandering rotor can result in fibrillation, in larger hearts, such as the sheep and possibly the human, fibrillation occurs in the form of a relatively small number of coexisting but short-lived rotors. Overall, the work discussed here has paved the way for a better understanding of the mechanisms of fibrillation in the normal, as well as diseased human heart. (c) 1998 American Institute of Physics. 相似文献
998.
Bowcock T Giles RT Hassard J Kinoshita K Pipkin FM Wilson R Wolinski J Xiao D Gentile T Haas P Hempstead M Jensen T Kagan H Kass R Behrends S Guida JM Guida JA Morrow F Poling R Thorndike EH Tipton P Alam MS Katayama N Kim IJ Sun CR Tanikella V Bortoletto D Chen A Garren L Goldberg M Holmes R Horwitz N Jawahery A Lubrano P Moneti GC Sharma V Csorna SE Mestayer MD Panvini RS Word GB Bean A Bobbink GJ Brock IC Engler A Ferguson T Kraemer RW Rippich C Vogel H Bebek C Berkelman K Blucher E 《Physical review letters》1987,58(4):307-310
999.
Alam MS Katayama N Kim IJ Li WC Lou XC Sun CR Tanikella V Bortoletto D Chen A Goldberg M Holmes R Horwitz N Jawahery A Lubrano P Moneti GC Sharma V Shipsey IP Thoma P Csorna SE Mestayer MD Panvini RS Word GB Bean A Bobbink GJ Brock IC Engler A Ferguson T Kraemer RW Rippich C Vogel H Bebek C Berkelman K Blucher E Cassel DG Copie T DeSalvo R DeWire JW Ehrlich R Galik RS Gilchriese MG Gittleman B Gray SW Halling AM Hartill DL Heltsley BK Holzner S Kandaswamy J Kowalewski R Kreinick DL Kubota Y 《Physical review letters》1987,59(1):22-25
1000.
Behrends S Guida JM Guida JA Morrow F Poling R Thorndike EH Tipton P Alam MS Katayama N Kim IJ Li WC Lou XC Sun CR Tanikella V Bortoletto D Chen A Goldberg M Holmes R Horwitz N Jawahery A Lubrano P Moneti GC Sharma V Shipsey IP Thoma P Csorna SE Mestayer MD Panvini RS Word GB Bean A Bobbink GJ Brock IC Engler A Ferguson T Kraemer RW Rippich C Vogel H Bebek C Berkelman K Blucher E Cassel DG Copie T DeSalvo R DeWire JW Ehrlich R Galik RS Gilchriese MG Gittelman B Gray SW Halling AM Hartill DL 《Physical review letters》1987,59(4):407-410