全文获取类型
收费全文 | 1238篇 |
免费 | 18篇 |
国内免费 | 31篇 |
专业分类
化学 | 668篇 |
晶体学 | 1篇 |
力学 | 34篇 |
数学 | 391篇 |
物理学 | 193篇 |
出版年
2018年 | 7篇 |
2016年 | 21篇 |
2015年 | 9篇 |
2014年 | 18篇 |
2013年 | 74篇 |
2012年 | 34篇 |
2011年 | 46篇 |
2010年 | 28篇 |
2009年 | 33篇 |
2008年 | 41篇 |
2007年 | 38篇 |
2006年 | 45篇 |
2005年 | 37篇 |
2004年 | 46篇 |
2003年 | 45篇 |
2002年 | 37篇 |
2001年 | 23篇 |
2000年 | 20篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 28篇 |
1994年 | 14篇 |
1993年 | 28篇 |
1992年 | 15篇 |
1991年 | 18篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 26篇 |
1981年 | 28篇 |
1980年 | 29篇 |
1979年 | 29篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1976年 | 19篇 |
1975年 | 14篇 |
1974年 | 17篇 |
1973年 | 24篇 |
1972年 | 11篇 |
1971年 | 8篇 |
1970年 | 7篇 |
1967年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有1287条查询结果,搜索用时 93 毫秒
1.
2.
3.
4.
From the N‐Heterocyclic Carbene‐Catalyzed Conjugate Addition of Alcohols to the Controlled Polymerization of (Meth)acrylates 下载免费PDF全文
Winnie Nzahou Ottou Damien Bourichon Dr. Joan Vignolle Anne‐Laure Wirotius Dr. Fredéric Robert Prof. Yannick Landais Dr. Jean‐Marc Sotiropoulos Dr. Karinne Miqueu Prof. Daniel Taton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9447-9453
Among various N‐heterocyclic carbenes (NHCs) tested, only 1,3‐bis(tert‐butyl)imidazol‐2‐ylidene (NHCtBu) proved to selectively promote the catalytic conjugate addition of alcohols onto (meth)acrylate substrates. This rather rare example of NHC‐catalyzed 1,4‐addition of alcohols was investigated as a simple means to trigger the polymerization of both methyl methacrylate and methyl acrylate (MMA and MA, respectively). Well‐defined α‐alkoxy poly(methyl (meth)acrylate) (PM(M)A) chains, the molar masses of which could be controlled by the initial [(meth)acrylate]0/[ROH]0 molar ratio, were ultimately obtained in N,N‐dimethylformamide at 25 °C. A hydroxyl‐terminated poly(ethylene oxide) (PEO‐OH) macro‐initiator was also employed to directly access PEO‐b‐PMMA amphiphilic block copolymers. Investigations into the reaction mechanism by DFT calculations revealed the occurrence of two competitive concerted pathways, involving either the activation of the alcohol or that of the monomer by NHCtBu. 相似文献
5.
Thierry Cazenave Flávio Dickstein Fred B. Weissler 《Journal of Dynamics and Differential Equations》2007,19(3):789-818
In this paper, we construct solutions u(t,x) of the heat equation on such that has nontrivial limit points in as t → ∞ for certain values of μ > 0 and β > 1/2. We also show the existence of solutions of this type for nonlinear heat equations.
相似文献
6.
Carlos García-Martínez Fred Glover Francisco J. Rodriguez Manuel Lozano Rafael Martí 《Computational Optimization and Applications》2014,58(1):161-185
The quadratic multiple knapsack problem (QMKP) consists in assigning a set of objects, which interact through paired profit values, exclusively to different capacity-constrained knapsacks with the aim of maximising total profit. Its many applications include the assignment of workmen to different tasks when their ability to cooperate may affect the results. Strategic oscillation (SO) is a search strategy that operates in relation to a critical boundary associated with important solution features (such as feasibility). Originally proposed in the context of tabu search, it has become widely applied as an efficient memory-based methodology. We apply strategic oscillation to the quadratic multiple knapsack problem, disclosing that SO effectively exploits domain-specific knowledge, and obtains solutions of particularly high quality compared to those obtained by current state-of-the-art algorithms. 相似文献
7.
Andrzej Chmura Sven Rustler Monica Paravidino Fred van Rantwijk Andreas Stolz Roger A. Sheldon 《Tetrahedron: Asymmetry》2013,24(19):1225-1232
Enantiomerically pure (S)-mandelic acid was synthesised from benzaldehyde by sequential hydrocyanation and hydrolysis in a bienzymatic cascade at starting concentrations up to 0.25 M. A cross-linked enzyme aggregate (CLEA) composed of the (S)-selective oxynitrilase from Manihot esculenta and the non-selective nitrilase from Pseudomonas fluorescens EBC 191 was employed as the biocatalyst. The nitrilase produces approx. equal amounts of (S)-mandelic acid and (S)-mandelic amide from (S)-mandelonitrile under standard conditions, but we surprisingly found that high (up to 0.5 M) concentrations of HCN induced a marked drift towards amide production. By including the amidase from Rhodococcus erythopolis in the CLEA we obtained (S)-mandelic acid as the sole product in 90% yield and >99% enantiomeric purity. 相似文献
8.
M. Fred Hoover 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):1327-1418
This paper is a literature survey of quaternary ammonium, sulfonium, and phosphonium polymers. 相似文献
9.
10.
Fred Espen Benth 《Applied Mathematical Finance》2018,25(1):36-65
The recent introduction of wind power futures written on the German wind power production index has brought with it new interesting challenges in terms of modelling and pricing. Some particularities of this product are the strong seasonal component embedded in the underlying, the fact that the wind index is bounded from both above and below and also that the futures are settled against a synthetically generated spot index. Here, we consider the non-Gaussian Ornstein–Uhlenbeck type processes proposed by Barndorff-Nielsen and Shephard in the context of modelling the wind power production index. We discuss the properties of the model and estimation of the model parameters. Further, the model allows for an analytical formula for pricing wind power futures. We provide an empirical study, where the model is calibrated to 37 years of German wind power production index that is synthetically generated assuming a constant level of installed capacity. Also, based on 1 year of observed prices for wind power futures with different delivery periods, we study the market price of risk. Generally, we find a negative risk premium whose magnitude decreases as the length of the delivery period increases. To further demonstrate the benefits of our proposed model, we address the pricing of European options written on wind power futures, which can be achieved through Fourier techniques. 相似文献