全文获取类型
收费全文 | 790篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 601篇 |
晶体学 | 14篇 |
力学 | 4篇 |
数学 | 77篇 |
物理学 | 118篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 22篇 |
2020年 | 30篇 |
2019年 | 18篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 8篇 |
2013年 | 41篇 |
2012年 | 38篇 |
2011年 | 53篇 |
2010年 | 34篇 |
2009年 | 15篇 |
2008年 | 51篇 |
2007年 | 37篇 |
2006年 | 53篇 |
2005年 | 34篇 |
2004年 | 38篇 |
2003年 | 28篇 |
2002年 | 28篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有814条查询结果,搜索用时 171 毫秒
31.
Robert G. Surbella III Korey P. Carter Trevor D. Lohrey Dallas Reilly Mark Kalaj Bruce K. McNamara Jon Schwantes Rebecca J. Abergel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(61):13819-13825
A new uranyl containing metal–organic framework, RPL-1 : [(UO2)2(C28H18O8)] . H2O (RPL for Radiochemical Processing Laboratory), was prepared, structurally characterized, and the solid-state photoluminescence properties explored. Single crystal X-ray diffraction data reveals the structure of RPL - 1 consists of two crystallographically unique three dimensional, interpenetrating nets with a 4,3-connected tbo topology. Each net contains large pores with an average width of 22.8 Å and is formed from monomeric, hexagonal bipyramidal uranyl nodes that are linked via 1,2,4,5-tetrakis(4-carboxyphenyl)benzene (TCPB) ligands. The thermal and photophysical properties of RPL-1 were investigated using thermogravimetric analysis and absorbance, fluorescence, and lifetime spectroscopies. The material displays excellent thermal stability and temperature dependent uranyl and TCPB luminescence. The framework is stable in aqueous media and due to the large void space (constituting 76 % of the unit cell by volume) can sequester organic dyes, the uptake of which induces a visible change to the color of the material. 相似文献
32.
33.
34.
Scott T. Parsell Sean M. Prendiville Trevor D. Wooley 《Geometric And Functional Analysis》2013,23(6):1962-2024
We obtain sharp estimates for multidimensional generalisations of Vinogradov’s mean value theorem for arbitrary translation-dilation invariant systems, achieving constraints on the number of variables approaching those conjectured to be the best possible. Several applications of our bounds are discussed. 相似文献
35.
36.
Acyl nitrile oxides are readily generated and trapped in a nitrating mixture with N-methylmaleimide. 相似文献
37.
38.
The predominant degradation reaction in the γ-irradiation of nine poly(olefin sulfone)s was found to be C-S bond scission with elimination of SO2 and olefin. The extent of depolymerization, measured by the yields of the two comonomers, increased over five irradiation temperatures from 0 to 150° C and could be correlated with the ceiling temperature. Thus G (total volatile products) increased from 10 to 10,000 over this temperature range. Minor radiolysis products included the alkanes corresponding to (1) loss of the side chain group and (2) scavenging of the side chain radical by monomer olefin. There was a deficiency of olefin relative to SO2, except at high temperatures, and isomerization of the product olefin in some cases. These observations are attributed to reactions of radiation-induced polymeric cations. 相似文献
39.
Dr. Thomas Hansen Dr. Alba Nin-Hill Prof. Dr. Jeroen D. C. Codée Dr. Trevor A. Hamlin Prof. Dr. Carme Rovira 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201649
The development of small-molecule covalent inhibitors and probes continuously pushes the rapidly evolving field of chemical biology forward. A key element in these molecular tool compounds is the “electrophilic trap” that allows a covalent linkage with the target enzyme. The reactivity of this entity needs to be well balanced to effectively trap the desired enzyme, while not being attacked by off-target nucleophiles. Here we investigate the intrinsic reactivity of substrates containing a class of widely used electrophilic traps, the three-membered heterocycles with a nitrogen (aziridine), phosphorus (phosphirane), oxygen (epoxide) or sulfur atom (thiirane) as heteroatom. Using quantum chemical approaches, we studied the conformational flexibility and nucleophilic ring opening of a series of model substrates, in which these electrophilic traps are mounted on a cyclohexene scaffold (C6H10Y with Y=NH, PH, O, S). It was revealed that the activation energy of the ring opening does not necessarily follow the trend that is expected from C−Y leaving-group bond strength, but steeply decreases from Y=NH, to PH, to O, to S. We illustrate that the HOMONu–LUMOSubstrate interaction is an all-important factor for the observed reactivity. In addition, we show that the activation energy of aziridines and phosphiranes can be tuned far below that of the corresponding epoxides and thiiranes by the addition of proper electron-withdrawing ring substituents. Our results provide mechanistic insights to rationally tune the reactivity of this class of popular electrophilic traps and can guide the experimental design of covalent inhibitors and probes for enzymatic activity. 相似文献
40.
Brønsted acid-catalyzed inverse-electron demand (IED) aza-Diels-Alder reactions between 2-aza-dienes and ethylene were studied using quantum chemical calculations. The computed activation energy systematically decreases as the basic sites of the diene progressively become protonated. Our activation strain and Kohn-Sham molecular orbital analyses traced the origin of this enhanced reactivity to i) “Pauli-lowering catalysis” for mono-protonated 2-aza-dienes due to the induction of an asynchronous, but still concerted, reaction pathway that reduces the Pauli repulsion between the reactants; and ii) “LUMO-lowering catalysis” for multi-protonated 2-aza-dienes due to their highly stabilized LUMO(s) and more concerted synchronous reaction path that facilitates more efficient orbital overlaps in IED interactions. In all, we illustrate how the novel concept of “Pauli-lowering catalysis” can be overruled by the traditional concept of “LUMO-lowering catalysis” when the degree of LUMO stabilization is extreme as in the case of multi-protonated 2-aza-dienes. 相似文献