全文获取类型
收费全文 | 337篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 239篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 46篇 |
物理学 | 65篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 16篇 |
2014年 | 10篇 |
2013年 | 20篇 |
2012年 | 26篇 |
2011年 | 35篇 |
2010年 | 12篇 |
2009年 | 15篇 |
2008年 | 20篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有355条查询结果,搜索用时 15 毫秒
51.
Conventional spin-echo magnetic resonance (MR) imaging of venous thrombosis is complicated by the variable appearance produced by the stage of blood clot degradation and velocity of blood flow. Phase MR imaging is a simple method based primarily on whether protons are stationary or moving. A case of superior sagittal sinus thrombosis demonstrates the utility of phase imaging. 相似文献
52.
Janne Martikainen Tuomo Rossi Jari Toivanen 《Numerical Linear Algebra with Applications》2002,9(8):629-652
A fast direct solution method for a discretized vector‐valued elliptic partial differential equation with a divergence constraint is considered. Such problems are typical in many disciplines such as fluid dynamics, elasticity and electromagnetics. The method requires the problem to be posed in a rectangle and boundary conditions to be either periodic boundary conditions or the so‐called slip boundary conditions in one co‐ordinate direction. The arising saddle‐point matrix has a separable form when bilinear finite elements are used in the discretization. Based on a result for so‐called p‐circulant matrices, the saddle‐point matrix can be transformed into a block‐diagonal form by fast Fourier transformations. Thus, the fast direct solver has the same structure as methods for scalar‐valued problems which are based on Fourier analysis and, therefore, it has the same computational cost ??(N log N). Numerical experiments demonstrate the good efficiency and accuracy of the proposed method. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
53.
54.
Nickel molybdate hydrate has been found to be an effective precursor catalyst for the hydrodesulfurization of thiophene. Calcination of the hydrate at 300°C and presulfidation with H2S are favorable treatments for higher activity.
, . 300°C H2S , .相似文献
55.
56.
Janne E TønderDavid Tanner 《Tetrahedron》2003,59(35):6937-6945
This paper deals with an approach to the enantioselective total synthesis of Lyngbyatoxin A, with focus on the stereocontrolled introduction of the quaternary stereogenic centre. The key step in the synthesis involves an enantiospecific Lewis-acid mediated rearrangement of chiral vinyl epoxides carrying a 7-substituted indole moiety. 相似文献
57.
58.
Richard M. Laine 《Transition Metal Chemistry》1980,5(1):158-159
Summary Photolysis of W(CO)o in the presence of cyclooctatetraene in hexane obtains sequential displacement of CO resulting in the formation of dihapto, tetrahapto and hexahapto complexes of cyclooctatetrae ne with tungsten. A simple preparation of 4-cyclooctatetraenetetracarbonyltungsten is described. 相似文献
59.
Gerrit Gobius du Sart Ivana Vukovic Zorica Vukovic Evgeny Polushkin Panu Hiekkataipale Janne Ruokolainen Katja Loos Gerrit ten Brinke 《Macromolecular rapid communications》2011,32(4):366-370
Supramolecular complexes of a poly(tert‐butoxystyrene)‐block‐polystyrene‐block‐poly(4‐vinylpyridine) triblock copolymers and less than stoichiometric amounts of pentadecylphenol (PDP) are shown to self‐assemble into a core–shell gyroid morphology with the core channels formed by the hydrogen‐bonded P4VP(PDP)complexes. After structure formation, PDP was removed using a simple washing procedure, resulting in well‐ordered nanoporous films that were used as templates for nickel plating.
60.
Thermoluminescence study of persistent luminescence materials: Eu2+- and R3+-doped calcium aluminates, CaAl2O4:Eu2+,R3+ 总被引:3,自引:0,他引:3
Aitasalo T Hölsä J Jungner H Lastusaari M Niittykoski J 《The journal of physical chemistry. B》2006,110(10):4589-4598
Thermoluminescence properties of the Eu2+-, R3+-doped calcium aluminate materials, CaAl2O4:Eu2+,R3+, were studied above room temperature. The trap depths were estimated with the aid of the preheating and initial rise methods. The seemingly simple glow curve of CaAl2O4:Eu2+ peaking at ca. 80 degrees C was found to correspond to several traps. The Nd3+ and Tm3+ ions, which enhance most the intensity of the high-temperature TL peaks, form the most suitable traps for intense and long-lasting persistent luminescence, too. The location of the 4f and 5d ground levels of the R3+ and R2+ ions were deduced in relation to the band structure of CaAl2O4. No clear correlation was found between the trap depths and the R3+ or R2+ level locations. The traps may thus involve more complex mechanisms than the simple charge transfer to (or from) the R3+ ions. A new persistent luminescence mechanism presented is based on the photoionization of the electrons from Eu2+ to the conduction band followed by the electron trapping to an oxygen vacancy, which is aggregated with a calcium vacancy and a R3+ ion. The migration of the electron from one trap to another and also to the aggregated R3+ ion forming R2+ (or R3+-e-) is then occurring. The reverse process of a release of the electron from traps to Eu2+ will produce the persistent luminescence. The ability of the R3+ ions to trap electrons is probably based on the different reduction potentials and size of the R3+ ions. Hole trapping to a calcium vacancy and/or the R3+ ion may also occur. The mechanism presented can also explain why Na+, Sm3+, and Yb3+ suppress the persistent luminescence. 相似文献