全文获取类型
收费全文 | 3784篇 |
免费 | 65篇 |
国内免费 | 13篇 |
专业分类
化学 | 1908篇 |
晶体学 | 24篇 |
力学 | 97篇 |
数学 | 505篇 |
物理学 | 1074篇 |
综合类 | 254篇 |
出版年
2021年 | 27篇 |
2020年 | 25篇 |
2019年 | 29篇 |
2018年 | 22篇 |
2017年 | 32篇 |
2016年 | 43篇 |
2015年 | 63篇 |
2014年 | 61篇 |
2013年 | 179篇 |
2012年 | 142篇 |
2011年 | 178篇 |
2010年 | 97篇 |
2009年 | 61篇 |
2008年 | 202篇 |
2007年 | 176篇 |
2006年 | 158篇 |
2005年 | 175篇 |
2004年 | 115篇 |
2003年 | 127篇 |
2002年 | 116篇 |
2001年 | 105篇 |
2000年 | 99篇 |
1999年 | 39篇 |
1998年 | 40篇 |
1997年 | 37篇 |
1996年 | 67篇 |
1995年 | 74篇 |
1994年 | 66篇 |
1993年 | 61篇 |
1992年 | 65篇 |
1991年 | 63篇 |
1990年 | 63篇 |
1989年 | 31篇 |
1988年 | 42篇 |
1987年 | 32篇 |
1986年 | 38篇 |
1985年 | 61篇 |
1984年 | 42篇 |
1983年 | 36篇 |
1982年 | 42篇 |
1981年 | 55篇 |
1980年 | 43篇 |
1979年 | 60篇 |
1978年 | 45篇 |
1977年 | 66篇 |
1976年 | 61篇 |
1975年 | 50篇 |
1974年 | 41篇 |
1973年 | 56篇 |
1972年 | 21篇 |
排序方式: 共有3862条查询结果,搜索用时 17 毫秒
1.
Aequationes mathematicae - In this paper, we establish a new class of dynamic inequalities of Hardy’s type which generalize and improve some recent results given in the literature. More... 相似文献
2.
Robert G. W. Anderson 《Ambix》2015,62(4):333-344
Following colonisation of South America by the Spanish, many new naturally occurring substances were sent to Europe. One of these was the silvery, unreactive metal, platinum, discovered in New Grenada in the mid-eighteenth century. It was often found in granular form, associated with gold, and the challenge to chemists was to refine it, produce it as wire or sheet, and determine its chemical properties. This interested the professor of chemistry at the University of Edinburgh, Joseph Black, who was able to obtain samples from London-based Spanish contacts, particularly Ignacio Luzuriaga. This paper examines how Black transmitted his knowledge of the metal to large numbers of students attending his annual course. 相似文献
3.
4.
Partially supported by NSF Grants. 相似文献
5.
Matroid bundles, introduced by MacPherson, are combinatorial analogues of real vector bundles. This paper sets up the foundations
of matroid bundles. It defines a natural transformation from isomorphism classes of real vector bundles to isomorphism classes
of matroid bundles. It then gives a transformation from matroid bundles to spherical quasifibrations, by showing that the
geometric realization of a matroid bundle is a spherical quasifibration. The poset of oriented matroids of a fixed rank classifies
matroid bundles, and the above transformations give a splitting from topology to combinatorics back to topology. A consequence
is that the mod 2 cohomology of the poset of rank k oriented matroids (this poset classifies matroid bundles) contains the free polynomial ring on the first k Stiefel-Whitney classes. 相似文献
6.
This paper presents an evaluation of the capability of turbulence models available in the commercial CFD code FLUENT 6.0 for their application to hydrofoil turbulent boundary layer separation flow at high Reynolds numbers. Four widely applied two‐equation RANS turbulence models were assessed through comparison with experimental data at Reynolds numbers of 8.284×106 and 1.657×107. They were the standard k–εmodel, the realizable k–εmodel, the standard k–ωmodel and the shear‐stress‐transport (SST) k–ωmodel. It has found that the realizable k–εturbulence model used with enhanced wall functions and near‐wall modelling techniques, consistently provides superior performance in predicting the flow characteristics around the hydrofoil. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
7.
Jeremy R. Lizotte Sara G. Anderson Timothy E. Long 《Journal of polymer science. Part A, Polymer chemistry》2004,42(7):1547-1556
A novel dinitroxide mediating agent that was suitable for stable free‐radical polymerization was synthesized and used in the block copolymerization of styrene and t‐butyl styrene. Quantitative yields of a novel dinitroxide based on 1,6‐hexamethylene diisocyanate and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy were obtained. Various experimental parameters, including the nitroxide‐to‐initiator molar ratio, were examined, and it was determined that the polymerization was most controlled under conditions similar to those of conventional 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated stable free‐radical polymerization. Moreover, the dinitroxide mediator proved to be a viable route for the facile two‐step synthesis of triblock copolymers of styrene and t‐butyl styrene. However, the dinitroxide mediation process resulted in a higher than expected level of nitroxide decomposition, which resulted in polymers possessing a terminal alkoxyamine and an adjacent hydroxylamine rather than a preferred internal bisalkoxyamine. This decomposition resulted in the formation of diblock copolymer species during the triblock copolymer synthesis. Gel permeation chromatography was used to monitor the chain‐end decomposition kinetics, and the determined observed rate constant (5.89 × 10?5 s?1) for decomposition agreed well with previous studies for other dinitroxide mediating agents. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1547–1556, 2004 相似文献
8.
Ross Anderson Cunsheng Ding Tor Helleseth Torleiv Klove 《Designs, Codes and Cryptography》1998,15(2):111-124
Previous researchers have designed shared control schemes with a view to minimising the likelihood that participants will conspire to perform an unauthorised act. But, human nature being what it is, systems inevitably fail; so shared control schemes should also be designed so that the police can identify conspirators after the fact. This requirement leads us to search for schemes with sparse access structures. We show how this can be done using ideas from coding theory. In particular, secret sharing schemes based on geometric codes whose dual [n,k,d] codes have d and n as their only nonzero weights are suitable. We determine their access structures and analyse their properties. We have found almost all of them, and established some relations among codes, designs and secret-sharing schemes. 相似文献
9.
10.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献