全文获取类型
收费全文 | 214334篇 |
免费 | 1770篇 |
国内免费 | 626篇 |
专业分类
化学 | 117416篇 |
晶体学 | 2919篇 |
力学 | 8349篇 |
综合类 | 6篇 |
数学 | 23305篇 |
物理学 | 64735篇 |
出版年
2020年 | 1970篇 |
2019年 | 2262篇 |
2018年 | 3204篇 |
2017年 | 3113篇 |
2016年 | 4266篇 |
2015年 | 2371篇 |
2014年 | 3817篇 |
2013年 | 9260篇 |
2012年 | 6890篇 |
2011年 | 8434篇 |
2010年 | 6071篇 |
2009年 | 5921篇 |
2008年 | 8137篇 |
2007年 | 8206篇 |
2006年 | 7629篇 |
2005年 | 6936篇 |
2004年 | 6166篇 |
2003年 | 5641篇 |
2002年 | 5497篇 |
2001年 | 5939篇 |
2000年 | 4684篇 |
1999年 | 3470篇 |
1998年 | 3007篇 |
1997年 | 3033篇 |
1996年 | 2823篇 |
1995年 | 2319篇 |
1994年 | 2419篇 |
1993年 | 2450篇 |
1992年 | 2595篇 |
1991年 | 2657篇 |
1990年 | 2559篇 |
1989年 | 2533篇 |
1988年 | 2463篇 |
1987年 | 2434篇 |
1986年 | 2357篇 |
1985年 | 2988篇 |
1984年 | 3147篇 |
1983年 | 2502篇 |
1982年 | 2777篇 |
1981年 | 2659篇 |
1980年 | 2466篇 |
1979年 | 2687篇 |
1978年 | 2797篇 |
1977年 | 2831篇 |
1976年 | 2800篇 |
1975年 | 2659篇 |
1974年 | 2637篇 |
1973年 | 2786篇 |
1972年 | 1850篇 |
1967年 | 1830篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
941.
We obtain asymptotic formulas for all the moments of certain arithmetic functions with linear recurrence sequences. We also apply our results to obtain asymptotic formulas for some mean values related to average orders of elements in finite fields. 相似文献
942.
943.
V. E. Bening V. Yu. Korolev S. Koksharov V. N. Kolokoltsov 《Journal of Mathematical Sciences》2007,146(4):5950-5958
944.
We analyze the critical length for design purposes of six-dimensional spaces invariant under translations and reflections
containing the functions 1, cos t and sin t. These spaces also contain the first degree polynomials as well as trigonometric and/or hyperbolic functions. We identify
the spaces whose critical length for design purposes is greater than 2π and find its maximum 4π. By a change of variables,
two biparametric families of spaces arise. We call shape preservation region to the set of admissible parameters in order
that the space has shape preserving representations for curves. We describe the shape preserving regions for both families.
To our friend Mariano Gasca on occasion of his 60th birthday
Research partially supported by the Spanish Research Grant MTM2006-03388, by Gobierno de Aragón and Fondo Social Europeo. 相似文献
945.
The process of electroforming (the production of a carboniferous conducting medium when the current flows through an organic
material under a high electric field) in open sandwichlike structures with an insulating gap several tens of nanometers in
width is considered. It is shown experimentally that there are factors that both favor (external ballast resistor) and prevent
(local spreading resistance and the presence of the initial conductivity in the insulating gap) the production of a single
conducting element between the electrodes. A simple model of the process in terms of the equivalent electric circuit is proposed.
The model helps to find the trade-off between these factors and to construct an I-V diagram, which exhibits a region within which a single conducting nanostructure can be electroformed. An expression that
relates the minimum permissible resistance of the nanostructure to its geometric parameters is derived. 相似文献
946.
M. E. Carlotti S. Sapino R. Cavalli M. Trotta F. Trotta K. Martina 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):445-450
This work deals with the formation of inclusion complexes between cinnamaldehyde and two synthetic alkylcarbonates of γ-cyclodextrin, namely ethylcarbonate-γ-CD and octylcarbonate-γ-CD. Complexation was monitored by phase-solubility studies, by FT-IR spectroscopy and by DSC and TG analysis.
The diffusion of cinnamaldehyde through a cellulose membrane was investigated in the absence and in the presence of each of
the two γ-CD alkylcarbonates. Studies on photostability and stability over time were carried out on different cosmetic formulations
containing pure cinnamaldehyde or an equivalent amount of cinnamaldehyde complexed with the two alkylcarbonates.
Phase-solubility diagrams, DSC, FTIR and TGA analysis suggested the formation of inclusion complexes. The diffusion of cinnamaldehyde
through the cellulose membrane decreased in the presence of the two alkylcarbonates confirming the interaction of this molecule
with the inclusion agents.
Moreover the stability of cinnamaldehyde to light and heat resulted increased by complexing this fragrance material with the
two alkylcarbonates. 相似文献
947.
On the capacitated vehicle routing problem 总被引:1,自引:0,他引:1
We consider the Vehicle Routing Problem, in which a fixed fleet of delivery vehicles of uniform capacity must service known
customer demands for a single commodity from a common depot at minimum transit cost. This difficult combinatorial problem
contains both the Bin Packing Problem and the Traveling Salesman Problem (TSP) as special cases and conceptually lies at the
intersection of these two well-studied problems. The capacity constraints of the integer programming formulation of this routing
model provide the link between the underlying routing and packing structures. We describe a decomposition-based separation
methodology for the capacity constraints that takes advantage of our ability to solve small instances of the TSP efficiently.
Specifically, when standard procedures fail to separate a candidate point, we attempt to decompose it into a convex combination
of TSP tours; if successful, the tours present in this decomposition are examined for violated capacity constraints; if not,
the Farkas Theorem provides a hyperplane separating the point from the TSP polytope. We present some extensions of this basic
concept and a general framework within which it can be applied to other combinatorial models. Computational results are given
for an implementation within the parallel branch, cut, and price framework SYMPHONY.
Received: October 30, 2000 / Accepted: December 19, 2001 Published online: September 5, 2002
Key words. vehicle routing problem – integer programming – decomposition algorithm – separation algorithm – branch and cut
Mathematics Subject Classification (2000): 20E28, 20G40, 20C20 相似文献
948.
E. Casarejos P. Armbruster L. Audouin J. Benlliure M. Bernas A. Boudard R. Legrain S. Leray B. Mustapha S. Czajkowski T. Enqvist B. Fernandez J. Pereira M. Pravikoff F. Rejmund K. -H. Schmidt C. Stephan J. Taieb L. Tassan-Got C. Villagrasa C. Volant W. Wlazlo 《Physics of Atomic Nuclei》2003,66(8):1413-1420
The isotopic production cross sections of heavy residues in relativistic heavy-ion collisions have been investigated in inverse kinematics. The primary reaction products were fully identified in mass and atomic number prior to beta decay using the fragment separator FRS. The huge collection of data obtained helps in the understanding of the two main reaction mechanisms involved: fragmentation and fission. These data provide basic information for future radioactive ion beam facilities and for technical applications like intense neutron sources by means of spallation targets. 相似文献
949.
950.