全文获取类型
收费全文 | 1386篇 |
免费 | 40篇 |
国内免费 | 1篇 |
专业分类
化学 | 886篇 |
晶体学 | 16篇 |
力学 | 19篇 |
数学 | 154篇 |
物理学 | 352篇 |
出版年
2021年 | 24篇 |
2020年 | 38篇 |
2019年 | 39篇 |
2017年 | 12篇 |
2016年 | 24篇 |
2015年 | 23篇 |
2014年 | 26篇 |
2013年 | 45篇 |
2012年 | 72篇 |
2011年 | 55篇 |
2010年 | 45篇 |
2009年 | 40篇 |
2008年 | 61篇 |
2007年 | 61篇 |
2006年 | 56篇 |
2005年 | 33篇 |
2004年 | 29篇 |
2003年 | 33篇 |
2002年 | 36篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 25篇 |
1997年 | 19篇 |
1996年 | 22篇 |
1995年 | 13篇 |
1994年 | 23篇 |
1993年 | 22篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1989年 | 12篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1985年 | 12篇 |
1984年 | 14篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 15篇 |
1979年 | 23篇 |
1978年 | 38篇 |
1977年 | 15篇 |
1976年 | 24篇 |
1975年 | 20篇 |
1974年 | 22篇 |
1973年 | 15篇 |
1972年 | 14篇 |
1971年 | 18篇 |
1970年 | 23篇 |
1969年 | 11篇 |
1968年 | 12篇 |
排序方式: 共有1427条查询结果,搜索用时 15 毫秒
71.
Zhenghai Yang Chao He Srinivas Doddipatla Vladislav S. Krasnoukhov Prof. Valeriy N. Azyazov Prof. Alexander M. Mebel Prof. Ralf I. Kaiser 《Chemphyschem》2020,21(17):1898-1904
The methylgermylene species (HGeCH3; X1A′) has been synthesized via the bimolecular gas phase reaction of ground state methylidyne radicals (CH) with germane (GeH4) under single collision conditions in crossed molecular beams experiments. Augmented by electronic structure calculations, this elementary reaction was found to proceed through barrierless insertion of the methylidyne radical in one of the four germanium-hydrogen bonds on the doublet potential energy surface yielding the germylmethyl (CH2GeH3; X2A′) collision complex. This insertion is followed by a hydrogen shift from germanium to carbon and unimolecular decomposition of the methylgermyl (GeH2CH3; X2A′) intermediate by atomic hydrogen elimination leading to singlet methylgermylene (HGeCH3; X1A′). Our investigation provides a glimpse at the largely unknown reaction dynamics and isomerization processes of the carbon-germanium system, which are quite distinct from those of the isovalent carbon system thus providing insights into the intriguing chemical bonding of organo germanium species on the most fundamental, microscopic level. 相似文献
72.
The compound with the general formula CnH2n+1 –COO–C6H4–C6H4–OOC–CnH2n+1, n = 14 (SYM- 14) crystallizes in the triclinic space group P 1 , with a = 5.431(5), b = 9.346(8), c = 39.172(51) Å, α = 92.60(15), β = 90.65(15), γ = 100.364(8)°. The crystal structure was solved by direct methods. Least-squares refinement leads to a final R value of 0.092 for 1575 observed reflections, with I > 2σs(I). The packing arrangement follows the same building principles found recently for the first three members of the well known homologous series of liquid crystalline terephthalylidine-anilines (TBAA-n). 相似文献
73.
Andriy Romanyuk Viktor Melnik Yaroslav Olikh Johannes Biskupek Ute Kaiser Martin Feneberg Klaus Thonke Peter Oelhafen 《Journal of luminescence》2010,130(1):87-91
Silicon clusters embedded in a silicon dioxide matrix were prepared by ultrasound-assisted implantation resulting in a modified concentration of suboxide states as revealed by high-resolution photoelectron spectroscopy. It is suggested that ultrasound treatment results in formation of different interface structure between silicon cluster and silicon dioxide matrix which is characterized by a distinctly reduced concentration of the suboxide states. It is observed that photoluminescence properties are strongly correlated with the concentration of the suboxide states thereby providing an evidence that besides a quantum confinement effect a closer look at the chemical composition of the nc-Si/SiO2 system is important. 相似文献
74.
75.
Advances in wide bandgap SiC for optoelectronics 总被引:1,自引:0,他引:1
Haiyan Ou Yiyu Ou Aikaterini Argyraki Saskia Schimmel Michl Kaiser Peter Wellmann Margareta K. Linnarsson Valdas Jokubavicius Jianwu Sun Rickard Liljedahl Mikael Syväjärvi 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(3):1-16
Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication. This paper will review the advances in fluorescent SiC for white light-emitting diodes, covering the poly-crystalline doped SiC source material growth, single crystalline epitaxy growth of fluorescent SiC, and nanofabrication of SiC to enhance the extraction efficiency for fluorescent SiC based white LEDs. 相似文献
76.
Samy Chammaa Dr. Bianca Sperl Anke G. Roth Aybike Yektaoglu Steffen Renner Dr. Thorsten Berg Prof. Dr. Christoph Arenz Prof. Dr. Athanassios Giannis Prof. Dr. Tudor I. Oprea Dr. Daniel Rauh Dr. Markus Kaiser Dr. Herbert Waldmann Prof. Dr. 《Angewandte Chemie (International ed. in English)》2010,49(21):3666-3670
77.
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
78.
Kaiser R Tilgner A 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):2949-2952
We investigate kinematic dynamos in cylinders and spheres surrounded by an insulator. The flow volume is divided into an inner region, in which the conducting fluid is in motion, and an outer region enclosing the inner one, in which the conductor is at rest. The dependence of the critical magnetic Reynolds number on the thickness of the outer conducting shell is discussed as well as implications for the design of experimental dynamos. 相似文献
79.
M.J. Kaiser 《Applied Mathematics Letters》1996,9(6):67-70
Based on Gage's notion of a “positive center” of a planar convex set, an ε-positive center figure is defined, constructed, and illustrated through example. The existence of an ε-positive center point, and the convexity of the ε-positive center figure, is conjectured. 相似文献
80.