全文获取类型
收费全文 | 981篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
化学 | 682篇 |
晶体学 | 3篇 |
力学 | 19篇 |
数学 | 190篇 |
物理学 | 110篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 34篇 |
2012年 | 50篇 |
2011年 | 40篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 45篇 |
2007年 | 44篇 |
2006年 | 45篇 |
2005年 | 40篇 |
2004年 | 57篇 |
2003年 | 40篇 |
2002年 | 32篇 |
2001年 | 11篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 17篇 |
1996年 | 19篇 |
1995年 | 24篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 17篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 17篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1973年 | 17篇 |
1972年 | 7篇 |
1971年 | 6篇 |
1931年 | 7篇 |
排序方式: 共有1004条查询结果,搜索用时 15 毫秒
991.
992.
Lukas Tendera Moritz Helm Dr. Mirjam J. Krahfuss Dr. Maximilian W. Kuntze-Fechner Prof. Dr. Udo Radius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(71):17849-17861
A case study on the effect of the employment of two different NHC ligands in complexes [Ni(NHC)2] (NHC=iPr2ImMe 1Me , Mes2Im 2 ) and their behavior towards alkynes is reported. The reaction of a mixture of [Ni2(iPr2ImMe)4(μ-(η2 : η2)-COD)] B / [Ni(iPr2ImMe)2(η4-COD)] B’ or [Ni(Mes2Im)2] 2 , respectively, with alkynes afforded complexes [Ni(NHC)2(η2-alkyne)] (NHC=iPr2ImMe: alkyne=MeC≡CMe 3 , H7C3C≡CC3H7 4 , PhC≡CPh 5 , MeOOCC≡CCOOMe 6 , Me3SiC≡CSiMe3 7 , PhC≡CMe 8 , HC≡CC3H7 9 , HC≡CPh 10 , HC≡C(p-Tol) 11 , HC≡C(4-tBu-C6H4) 12 , HC≡CCOOMe 13 ; NHC=Mes2Im: alkyne=MeC≡CMe 14 , MeOOCC≡CCOOMe 15 , PhC≡CMe 16 , HC≡C(4-tBu-C6H4) 17 , HC≡CCOOMe 18 ). Unusual rearrangement products 11 a and 12 a were identified for the complexes of the terminal alkynes HC≡C(p-Tol) and HC≡C(4-tBu-C6H4), 11 and 12 , which were formed by addition of a C−H bond of one of the NHC N-iPr methyl groups to the C≡C triple bond of the coordinated alkyne. Complex 2 catalyzes the cyclotrimerization of 2-butyne, 4-octyne, diphenylacetylene, dimethyl acetylendicarboxylate, 1-pentyne, phenylacetylene and methyl propiolate at ambient conditions, whereas 1Me is not a good catalyst. The reaction of 2 with 2-butyne was monitored in some detail, which led to a mechanistic proposal for the cyclotrimerization at [Ni(NHC)2]. DFT calculations reveal that the differences between 1M e and 2 for alkyne cyclotrimerization lie in the energy profile of the initiation steps, which is very shallow for 2 , and each step is associated with only a moderate energy change. The higher stability of 3 compared to 14 is attributed to a better electron transfer from the NHC to the metal to the alkyne ligand for the N-alkyl substituted NHC, to enhanced Ni-alkyne backbonding due to a smaller CNHC−Ni−CNHC bite angle, and to less steric repulsion of the smaller NHC iPr2ImMe. 相似文献
993.
Active diffusiophoresis-swimming through interaction with a self-generated, neutral, solute gradient-is a paradigm for autonomous motion at the micrometer scale. We study this propulsion mechanism within a linear response theory. First, we consider several aspects relating to the dynamics of the swimming particle. We extend established analytical formulae to describe small swimmers, which interact with their environment on a finite lengthscale. Solute convection is also taken into account. Modeling of the chemical reaction reveals a coupling between the angular distribution of reactivity on the swimmer and the concentration field. This effect, which we term "reaction induced concentration distortion," strongly influences the particle speed. Building on these insights, we employ irreversible, linear thermodynamics to formulate an energy balance. This approach highlights the importance of solute convection for a consistent treatment of the energetics. The efficiency of swimming is calculated numerically and approximated analytically. Finally, we define an efficiency of transport for swimmers which are moving in random directions. It is shown that this efficiency scales as the inverse of the macroscopic distance over which transport is to occur. 相似文献
994.
After a brief account of the present knowledge on the mechanism of the allylnickel complex catalyzed stereospecific butadiene polymerization, synthesis and catalytic properties of the cationic allylnickel(II) complexes, [C3H5NiL2]PF6 (L = P(OAlk)3, P(OAr)3, PPh3, AsPh3, SbPh3, MeCN, Me3CNC, 1,5–COD), are described. From kinetic and 31P-NMR spectroscopic investigations, especially with [C3H5Ni(P(OPh)3)2]PF6 as a typical trans-catalyst, the definite course of the catalytic stereoregulation has been elucidated. 相似文献
995.
Stephan Jüngling Rolf Mülhaupt Udo Stehling Hans-Herbert Brintzinger David Fischer Franz Langhauser 《Macromolecular Symposia》1995,97(1):205-216
Propene polymerization of methylalumoxane (MAO) activated rac-Me2Si(Benz[e]Indenyl)2ZrCl2 ( BI ) and rac-Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2 ( MBI ) was studied to investigate the influence of the ligand substitution pattern and the role of dormant sites. Poly(propene) end group composition as well as regio- and stereoirregularities were examined by means of 1H- and 13C-NMR spectroscopy. Dormant sites, resulting from 2, 1-propene insertion, were reactivated either by β-hydrogen transfer to propene, yielding 2-butenyl end groups, or by 1, 2-insertion of propene, yielding regioirregularities. Propene polymerization in the presence of hydrogen gave n-butyl end groups and less regioirregularities as expected for hydrogenolysis of such dormant sites. Methyl substitution in 2-position of the benz[e]indenyl ligand suppressed β-hydrogen transfer to propene, and increased molecular weight with increasing propene concentration. Also, activation energy increased from 30 kJ/mol ( BI /MAO) to 59 kJ/mol ( MBI /MAO). For both catalysts activity depended on propene concentration. The order of reaction relative to propene was 1.7. 相似文献
996.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
997.
A new morphology of ternary ABC triblock copolymers is presented which results from the asymmetric interaction between a centre block (poly(ethylene-co-butene)) to different end blocks (polystyrene and poly(methyl methacrylate)). This morphology with the appearance of a “knitting pattern” can be described as an intermediate of a morphology of A, B and C lamellae and a morphology of A and C lamellae with B cylinders at the A/C interface. 相似文献
998.
999.
1000.
The influence of a styrene-ethylene/butylene-styrene triblock copolymer (SEBS) on an isotactic polypropylene / polyethylene blend was investigated. For comparison binary blends with polypropylene and SEBS alone were also prepared. The blends obtained by solution mixing were characterised by small-angle x-ray scattering, light microscopy and dynamic mechanical analysis. The role of SEBS as matrix reinforcer or interfacial agent is composition dependent. Experimental data also reveal a different influence of SEBS on the binary blends than on the ternary blends containing polyethylene. 相似文献