全文获取类型
收费全文 | 415661篇 |
免费 | 22751篇 |
国内免费 | 1314篇 |
专业分类
化学 | 260186篇 |
晶体学 | 4845篇 |
力学 | 16648篇 |
综合类 | 11篇 |
数学 | 51005篇 |
物理学 | 107031篇 |
出版年
2023年 | 5261篇 |
2021年 | 4878篇 |
2020年 | 7128篇 |
2019年 | 4998篇 |
2018年 | 5418篇 |
2017年 | 3569篇 |
2016年 | 10953篇 |
2015年 | 9928篇 |
2014年 | 10651篇 |
2013年 | 22450篇 |
2012年 | 17657篇 |
2011年 | 18673篇 |
2010年 | 13958篇 |
2009年 | 13456篇 |
2008年 | 17004篇 |
2007年 | 16879篇 |
2006年 | 15569篇 |
2005年 | 14327篇 |
2004年 | 12704篇 |
2003年 | 10958篇 |
2002年 | 10548篇 |
2001年 | 11117篇 |
2000年 | 8623篇 |
1999年 | 6814篇 |
1998年 | 5469篇 |
1997年 | 5337篇 |
1996年 | 5522篇 |
1995年 | 4973篇 |
1994年 | 4749篇 |
1993年 | 4684篇 |
1992年 | 5058篇 |
1991年 | 4813篇 |
1990年 | 4484篇 |
1989年 | 4285篇 |
1988年 | 4563篇 |
1987年 | 4221篇 |
1986年 | 4048篇 |
1985年 | 5854篇 |
1984年 | 5932篇 |
1983年 | 4764篇 |
1982年 | 5235篇 |
1981年 | 5275篇 |
1980年 | 5066篇 |
1979年 | 5121篇 |
1978年 | 5134篇 |
1977年 | 5190篇 |
1976年 | 5205篇 |
1975年 | 5157篇 |
1974年 | 5028篇 |
1973年 | 5051篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
11.
We study the full counting statistics of transport electrons through a semiconductor two-level quantum dot with Rashba spin–orbit (SO) coupling, which acts as a nonabelian gauge field and thus induces the electron transition between two levels along with the spin flip. By means of the quantum master equation approach, shot noise and skewness are obtained at finite temperature with two-body Coulomb interaction. We particularly demonstrate the crucial effect of SO coupling on the super-Poissonian fluctuation of transport electrons, in terms of which the SO coupling can be probed by the zero-frequency cumulants. While the charge currents are not sensitive to the SO coupling. 相似文献
12.
13.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters 下载免费PDF全文
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
14.
15.
16.
17.
18.
19.
Triesterase and Promiscuous Diesterase Activities of a Di‐CoII‐Containing Organophosphate Degrading Enzyme Reaction Mechanisms 下载免费PDF全文
Dr. Marta E. Alberto Gaspar Pinto Prof. Nino Russo Dr. Marirosa Toscano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3736-3745
The reaction mechanism for the hydrolysis of trimethyl phosphate and of the obtained phosphodiester by the di‐CoII derivative of organophosphate degrading enzyme from Agrobacterium radiobacter P230(OpdA), have been investigated at density functional level of theory in the framework of the cluster model approach. Both mechanisms proceed by a multistep sequence and each catalytic cycle begins with the nucleophilic attack by a metal‐bound hydroxide on the phosphorus atom of the substrate, leading to the cleavage of the phosphate‐ester bond. Four exchange‐correlation functionals were used to derive the potential energy profiles in protein environments. Although the enzyme is confirmed to work better as triesterase, as revealed by the barrier heights in the rate‐limiting steps of the catalytic processes, its promiscuous ability to hydrolyze also the product of the reaction has been confirmed. The important role played by water molecules and some residues in the outer coordination sphere has been elucidated, while the binuclear CoII center accomplishes both structural and catalytic functions. To correctly describe the electronic configuration of the d shell of the metal ions, high‐ and low‐spin arrangement jointly with the occurrence of antiferromagnetic coupling, have been herein considered. 相似文献
20.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献