全文获取类型
收费全文 | 2619篇 |
免费 | 51篇 |
国内免费 | 11篇 |
专业分类
化学 | 1577篇 |
晶体学 | 17篇 |
力学 | 84篇 |
数学 | 589篇 |
物理学 | 414篇 |
出版年
2021年 | 31篇 |
2020年 | 23篇 |
2019年 | 30篇 |
2016年 | 42篇 |
2015年 | 54篇 |
2014年 | 42篇 |
2013年 | 107篇 |
2012年 | 85篇 |
2011年 | 101篇 |
2010年 | 58篇 |
2009年 | 55篇 |
2008年 | 99篇 |
2007年 | 73篇 |
2006年 | 63篇 |
2005年 | 56篇 |
2004年 | 50篇 |
2003年 | 35篇 |
2002年 | 50篇 |
2001年 | 26篇 |
2000年 | 41篇 |
1999年 | 45篇 |
1998年 | 32篇 |
1997年 | 38篇 |
1996年 | 29篇 |
1995年 | 37篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 35篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 31篇 |
1987年 | 33篇 |
1986年 | 28篇 |
1985年 | 47篇 |
1984年 | 34篇 |
1983年 | 24篇 |
1982年 | 29篇 |
1981年 | 34篇 |
1980年 | 39篇 |
1979年 | 36篇 |
1978年 | 24篇 |
1977年 | 43篇 |
1976年 | 32篇 |
1975年 | 25篇 |
1974年 | 21篇 |
1971年 | 20篇 |
1967年 | 18篇 |
1933年 | 20篇 |
1930年 | 21篇 |
排序方式: 共有2681条查询结果,搜索用时 31 毫秒
51.
52.
We calculate the continuous cohomology of the Lie algebra of meromorphic vector fields on a compact Riemann surface from the cohomology of the holomorphic vector fields on the open Riemann surface pointed in the poles. This cohomology has been given by Kawazumi. Our result shows the Feigin–Novikov conjecture. 相似文献
53.
One admires rotational staircases in classical buildings since centuries. In particular, we are fascinated and inspired by the beautiful winding staircase (please, regard the picture below) in the center of the recently constructed University Library of the Brandenburgian Technical University at Cottbus by the bureau of architects Herzog & de Meuron from Basel. The sophisticated mathematician directly recognizes this staircase being a rotational minimal surface – namely the well-known helicoid – with a multiply covering projection onto the plane, solving a semi-free boundary value problem. We now ask the question, in which class of surfaces this helicoid is uniquely determined. Furthermore, we examine in how far the boundary values can be perturbed such that neighboring surfaces still exist. Both questions being affirmatively answered, we receive the stability of this boundary value problem. Finally, we investigate that our surface realizes a global minimum of area in the class of all parametric minimal surfaces solving an adequate mixed boundary value problem. Here we study one-to-one harmonic mappings onto the universal covering of the plane. This is achieved on the basis of our joint investigations with Professor Stefan Hildebrandt from the University of Bonn. Since H. Catalan was the first to classify the helicoid among ruled minimal surfaces and J. Plateau contributed, besides his inspiring experiments with soap bubbles, also his name to our central problem, I would like to present this treatise in the French language. During the construction of our University Library I got acquainted to the responsible architect for this project from the bureau Herzog & de Meuron, Frau Christine Binswanger and would like to dedicate this work to her with great respect. In her home city of Basel, classical Analysis could originally be developed by members of the Bernoulli family and Leonhard Euler. 相似文献
54.
55.
Hongxin Wang Anthony T. Young Jinghua Guo Stephen P. Cramer Stephan Friedrich Artur Braun Weiwei Gu 《Journal of synchrotron radiation》2013,20(4):614-619
X‐ray absorption and scattering spectroscopies involving the 3d transition‐metal K‐ and L‐edges have a long history in studying inorganic and bioinorganic molecules. However, there have been very few studies using the M‐edges, which are below 100 eV. Synchrotron‐based X‐ray sources can have higher energy resolution at M‐edges. M‐edge X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) could therefore provide complementary information to K‐ and L‐edge spectroscopies. In this study, M2,3‐edge XAS on several Co, Ni and Cu complexes are measured and their spectral information, such as chemical shifts and covalency effects, are analyzed and discussed. In addition, M2,3‐edge RIXS on NiO, NiF2 and two other covalent complexes have been performed and different d–d transition patterns have been observed. Although still preliminary, this work on 3d metal complexes demonstrates the potential to use M‐edge XAS and RIXS on more complicated 3d metal complexes in the future. The potential for using high‐sensitivity and high‐resolution superconducting tunnel junction X‐ray detectors below 100 eV is also illustrated and discussed. 相似文献
56.
The transition between insulator and metal conductor states, induced by oxygen non-stoichiometry, was studied for NaNbO3 : Mn crystals. Conditions for an optimal reduction were determined on the basis of TGA tests. The temperature dependencies of the resistance measured on the macroscale showed that the transition from thermally activated to metallic features depends on the level of oxygen deficiency. The LC-AFM measurement exhibited non-homogeneous electric resistance on the nanoscale. We ascribed the local insulator–metal transition to changeover in the electronic state of the Nb ions occurring in filaments. The Mn dopant stabilised the induced oxygen non-stoichiometry and the metallic conduction down to room temperature. 相似文献
57.
The 0/1 primal separation problem is: Given an extreme point xˉ of a 0/1 polytope P and some point x
*, find an inequality which is tight at xˉ, violated by x
* and valid for P or assert that no such inequality exists. It is known that this separation variant can be reduced to the standard separation
problem for P.
We show that 0/1 optimization and 0/1 primal separation are polynomial time equivalent. This implies that the problems 0/1
optimization, 0/1 standard separation, 0/1 augmentation, and 0/1 primal separation are polynomial time equivalent.
Then we provide polynomial time primal separation procedures for matching, stable set, maximum cut, and maximum bipartite
graph problems, giving evidence that these algorithms are conceptually simpler and easier to implement than their corresponding
counterparts for standard separation. In particular, for perfect matching we present an algorithm for primal separation that
rests only on simple max-flow computations. In contrast, the known standard separation method relies on an explicit minimum
odd cut algorithm. Consequently, we obtain a very simple proof that a maximum weight perfect matching of a graph can be computed
in polynomial time.
Received: August 20, 2001 / Accepted: April 2002 Published online: December 9, 2002
RID="⋆"
ID="⋆" This research was developed while the author was on leave at the Istituto di Analisi dei Sistemi ed Informatica, Viale
Manzoni 30, 00185 Roma, supported by the project TMR-DONET nr. ERB FMRX-CT98-0202 of the European Union.
Mathematics Subject Classification (2000): 90C10, 90C60, 90C57 相似文献
58.
Christian J. -F. Dupraz Patrick Nickels Udo Beierlein Wendy U. Huynh Friedrich C. Simmel 《Superlattices and Microstructures》2003,33(5-6):369
This paper provides an overview of recent research developments in the field of nanoelectronics with organic materials such as carbon nanotubes and DNA-templated nanowires. Carbon nanotubes and gold electrodes are chemically functionalized in order to contact carbon nanotubes by self-assembly. The transport properties of these nanotubes are dominated by charging effects and display clear Coulomb blockade behaviour. A different approach towards nanoscale electronics is based on the molecular recognition properties of biomolecules such as DNA. As an example, DNA is stretched between electrodes using a molecular combing technique. A two-step metallization procedure leads to the formation of highly conductive gold nanowires. 相似文献
59.
The theory of physical dimensions and units in physics is outlined. This includes a discussion of the universal applicability and superiority of quantity equations. The International System of Units (SI) is one example thereof. By analyzing mechanics and electrodynamics, it naturally leads one, besides the dimensions of length and time, to the fundamental units of action , electric charge q, and magnetic flux ?. Also, and are known. These results of classical physics suggests to look into the corresponding quantum aspects of q and ? (and also of ): The electric charge occurs exclusively in elementary charges e, whereas the magnetic flux can have any value; in specific situations, however, in superconductors of type II at very low temperatures, ? appears quantized in the form of fluxons (Abrikosov vortices). And leads, of course, to the Planck quantum h. Thus, one is directed to superconductivity and, because of the resistance, to the quantum Hall effect. In this way, the Josephson and the quantum Hall effects come into focus quite naturally. One goal is to determine the behavior of the fundamental constants in special and in general relativity. 相似文献
60.
Bo?Feng Sarada?Bulchand Emre?Yaksi Rainer?W?Friedrich Suresh?JesuthasanEmail author 《BMC neuroscience》2005,6(1):46