全文获取类型
收费全文 | 4105篇 |
免费 | 702篇 |
国内免费 | 670篇 |
专业分类
化学 | 4266篇 |
晶体学 | 17篇 |
力学 | 169篇 |
综合类 | 6篇 |
数学 | 204篇 |
物理学 | 815篇 |
出版年
2024年 | 30篇 |
2023年 | 360篇 |
2022年 | 138篇 |
2021年 | 148篇 |
2020年 | 229篇 |
2019年 | 168篇 |
2018年 | 152篇 |
2017年 | 113篇 |
2016年 | 282篇 |
2015年 | 239篇 |
2014年 | 236篇 |
2013年 | 314篇 |
2012年 | 209篇 |
2011年 | 243篇 |
2010年 | 173篇 |
2009年 | 263篇 |
2008年 | 248篇 |
2007年 | 245篇 |
2006年 | 231篇 |
2005年 | 179篇 |
2004年 | 191篇 |
2003年 | 134篇 |
2002年 | 88篇 |
2001年 | 68篇 |
2000年 | 84篇 |
1999年 | 74篇 |
1998年 | 75篇 |
1997年 | 63篇 |
1996年 | 60篇 |
1995年 | 53篇 |
1994年 | 39篇 |
1993年 | 42篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 20篇 |
1988年 | 32篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 26篇 |
1984年 | 11篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 12篇 |
1975年 | 8篇 |
1973年 | 9篇 |
1972年 | 5篇 |
排序方式: 共有5477条查询结果,搜索用时 933 毫秒
51.
This article examines the current status of Markov processes in single molecule fluorescence. For molecular dynamics to be described by a Markov process, the Markov process must include all states involved in the dynamics and the first-passage time (FPT) distributions out of those states must be describable by a simple exponential law. The observation of non-exponential FPT distributions or other evidence of non-Markovian dynamics is common in single molecule studies and offers an opportunity to expand the Markov model to include new dynamics or states that improve understanding of the system. 相似文献
52.
A comprehensive B3LYP/6-31+G∗ study of the influence of BF3 on the [4+2] cycloaddition of vinylketene with formaldimine was conducted. For this purpose, the complete pathway was determined and changes in different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χanis, and the nucleus-independent chemical shifts, NICS) were monitored along the reaction profile with a view to estimate the aromatization associated to the process. We have also applied the ACID (anisotropy of the current-induced density) method with the same intention. 相似文献
53.
Gibson SE Kaufmann KA Loch JA Steed JW White AJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2566-2576
Understanding the interaction of chiral ligands, alkynes, and alkenes with cobaltcarbonyl sources is critical to learning more about the mechanism of the catalytic, asymmetric Pauson-Khand reaction. We have successfully characterized complexes of the type [Co2(alkyne)(binap)(CO)4] (BINAP=(1,1'-binaphthalene)-2,2'-diylbis(diphenylphosphine)) and shown that diastereomer interconversion occurs under Pauson-Khand reaction conditions when alkyne=HC[triple bond]CCO2Me. Attempts to isolate [Co2(alkyne)(binap)(CO)x] complexes with coordinated alkenes led to the formation of cobaltacyclopentadiene species. 相似文献
54.
Lam WH Jia G Lin Z Lau CP Eisenstein O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(12):2775-2782
Theoretical calculations on the metathesis process, [Tp(PH3)MR(eta 2-H[bond]CH3)] --> [Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe, Ru, and Os; R=H and CH3), have been systematically carried out to study their detailed reaction mechanisms. Other than the one-step mechanism via a four-center transition state and the two-step mechanism through an oxidative addition/reductive elimination pathway, a new one-step mechanism, with a transition state formed under oxidative addition, has been found. Based on the intrinsic reaction coordinate calculations, we found that the trajectories of the transferring hydrogen atom in the metathesis processes studied are similar to each other regardless of the nature of reaction mechanisms. 相似文献
55.
聚双环戊二烯反应注射成型 总被引:3,自引:0,他引:3
本文介绍了国外有关聚双环戊二烯反应注射成型的研究进展,讨论了国内进行聚双环戊二烯反应注射成型开发研究的现实意义,并对这一领域的发展进行了展望 相似文献
56.
Summary The calculation of vibrational states using a gradient extremal path is discussed. Gradient extremal paths are defined by local criteria, which lead to stable solutions. This has certain advantages in comparison with a steepest-descent path, which is often difficult to determine accurately. For cases where a reaction path formalism is applicable, a path based on the gradient extremal concept gives results in close agreement with those obtained using traditional steepest-descent methods. We present algorithms for carrying out such calculations and also give some numerical results. 相似文献
57.
Gavernet Luciana Saraví Cisneros Hebe Saraví Bruno-Blanch Luis E. Estiú Gguillerminal L. 《Theoretical chemistry accounts》2003,110(6):434-440
A theoretical study of the mechanisms associated with the synthesis of anticonvulsant symmetric N,N-substituted sulfamides is presented. Two possible synthetic routes are compared, which mainly differ in the use of pyridine as a nucleophilic agent in the reaction mechanism. Geometry optimization techniques and transition-state detection at the B3LYP/6-31G** level, modeling the solvent by means of an isodensity polarizable continuum approach, allow the most suitable method for the experimental process to be discerned.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002) 相似文献
58.
《Electroanalysis》2004,16(8):650-655
An analytical solution is developed for heterogeneous ECE processes occurring at channel electrode surface for both laminar and turbulent flow. The solution explicitly links the behavior of ECE processes and the parameters. A simple expression of the effective number of electrons transferred, covering all the reaction rate constants and different diffusion coefficients of the reactant A and the intermediate product B, is obtained. Excellent agreement with previous numerical and analytical results is shown . Parametric studies illustrate the effects of diffusion coefficients, hydrodynamic factors and reaction rate constants on the effective number of electrons transferred and the currents. 相似文献
59.
In this paper we propose a method for carrying out variational transition state theory calculations without first obtaining
a converged minimum-energy path (MEP). We illustrate the method in two ways, first of all by employing an unconverged MEP
and secondly by using a dynamically optimized distinguished reaction path. Preliminary tests of the algorithm for the reactions
OH+H2→H2O+H and C2H5→C2H4+H are very encouraging.
Received: 22 January 1997 / Accepted: 11 March 1997 相似文献
60.
用停止-流动分光光度法研究了Eu~(2+)与二甲酚橙(XO)间快速电子转移反应的动力学规律。求得了速控步骤的动力学参数。如反应级数(n=2)、几个不同温度下的速率常数(k_(278 K)=5.7×10~8 L·mol~-·s~(-1), k_(s38 K)=1.01×10~9 L·mol~(-1)·s~(-1))、活化能(E=7.6×10~3 J·mol~(-1)), 以及指前因子(A=1.5×10~(10) L·mol~(-1)·s~(-1)), 并判断出其为溶液中扩散控制型反应。根据实验现象与测试结果, 提出了Eu~(2+)与XO的反应分别在Eu~(2+)相对过量和在XO过量时的反应机理, 并判断了各反应步骤速率常数之间的相对关系。 相似文献