全文获取类型
收费全文 | 2150篇 |
免费 | 108篇 |
国内免费 | 13篇 |
专业分类
化学 | 1587篇 |
晶体学 | 10篇 |
力学 | 65篇 |
数学 | 328篇 |
物理学 | 281篇 |
出版年
2024年 | 6篇 |
2023年 | 15篇 |
2022年 | 36篇 |
2021年 | 41篇 |
2020年 | 31篇 |
2019年 | 42篇 |
2018年 | 35篇 |
2017年 | 41篇 |
2016年 | 89篇 |
2015年 | 55篇 |
2014年 | 110篇 |
2013年 | 133篇 |
2012年 | 166篇 |
2011年 | 189篇 |
2010年 | 111篇 |
2009年 | 114篇 |
2008年 | 147篇 |
2007年 | 133篇 |
2006年 | 122篇 |
2005年 | 113篇 |
2004年 | 114篇 |
2003年 | 83篇 |
2002年 | 72篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 22篇 |
1998年 | 23篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 17篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1971年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有2271条查询结果,搜索用时 15 毫秒
991.
The calculation of quantum similarity measures from second-order density functions contracted to intracule and extracule
densities obtained at the Hartree-Fock level is presented and applied to a series of atoms, (He, Li, Be, and Ne), isoelectronic
molecules (C2H2, HCN, CNH, CO, and N2), and model hydrogen-transfer processes (H2/H+, H2/Hot, H2/H−). Second-order quantum similarity measures and indices are found to be suitable measures for quantitatively analyzing electron-pair
density reorganizations in atoms, molecules, and chemical processes. For the molecular series, a comparative analysis between
the topology of pairwise similarity functions as computed from one-electron, intracule, and extracule densities is carried
out and the assignment of each particular local similarity maximum to a molecular alignment discussed. In the comparative
study of the three hydrogen-transfer reactions considered, second-order quantum similarity indices are found to be more sensitive
than first-order indices for analyzing the electron-density reorganization between the reactant complex and the transition
state, thus providing additional insights for a better understanding of the mechanistic aspects of each process.
Received: 7 July 1997 / Accepted: 29 October 1997 相似文献
992.
Alexey N. Bilyachenko Mikhail M. Levitsky Alexey I. Yalymov Alexander A. Korlyukov Viktor N. Khrustalev Anna V. Vologzhanina Lidia S. Shul'pina Nikolay S. Ikonnikov Alexander E. Trigub Pavel V. Dorovatovskii Xavier Bantreil Frdric Lamaty Jrme Long Joulia Larionova Igor E. Golub Elena S. Shubina Georgiy B. Shul'pin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(49):15586-15589
A series of four unprecedented heterometallic metallagermsesquioxanes were synthesized. Their cage‐like architectures have a unique type of molecular topology consisting of the hexairon oxo {Fe6O19} core surrounded in a triangular manner by three cyclic germoxanolates [PhGe(O)O]5. This structural organization induces antiferromagnetic interactions between the FeIII ions through the oxygen atoms. Evaluated for this first time in catalysis, these compounds showed a high catalytic activity in the oxidation of alkanes and the oxidative formation of benzamides from alcohols. 相似文献
993.
994.
Frederic Gyselinck Ulrich Maschke Andre Traisnel Xavier Coqueret 《Liquid crystals》2013,40(3):421-428
Polymer dispersed liquid crystal (PDLC) films were prepared by polymerization-induced phase separation processes using ultraviolet (UV) and electron beam (EB) radiation. A mixture of the nematic LC material E7, an aromatic polyester acrylate, and additional monomeric acrylates was exposed to the EB radiation. A photoinitiator was included in the initial mixture in the case of UV exposure. The electro-optical behaviour of the PDLC films obtained has been investigated as a function of the chosen radiation. The transmission versus voltage curves strongly depend on the curing conditions, and are highly reproducible. Threshold and saturation voltages continuously increase with increasing dose values for UV-cured films, whereas plateau values were reached for EB-cured samples. A small memory effect has been observed for UV-cured systems. 相似文献
995.
Xavier Moreau Jean-Philippe Goddard Serge Thorimbert 《Journal of organometallic chemistry》2009,694(4):561-565
The platinum- and gold-catalyzed cycloisomerization of enyne systems has been carried out in various ionic liquids (ILs). In some cases, better selectivities and shorter reaction times have been observed compared to conventional conditions. 相似文献
996.
Mathematical constructions and comparisons of accurate absorbing boundary conditions for the one-dimensional Schrödinger equation with a general variable repulsive potential are developed. Stable semi-discretization schemes are built for the associated initial boundary value problems. Finally, some numerical simulations give a comparison of the various absorbing boundary conditions and show that they yield accurate computations. 相似文献
997.
998.
Dr. Francisco Núñez‐Zarur Dr. Xavier Solans‐Monfort Prof. Roser Pleixats Dr. Luis Rodríguez‐Santiago Prof. Mariona Sodupe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(43):14553-14565
DFT (B3LYP‐D) calculations have been used to better understand the origin of the recovered Hoveyda–Grubbs derivative catalysts after ring‐closing diene or enyne metathesis reactions. For that, we have considered the activation process of five different Hoveyda–Grubbs precursors in the reaction with models of usual diene and enyne reactants as well as the potential precursor regeneration through the release/return mechanism. The results show that, regardless of the nature of the initial precursor, the activation process needs to overcome relatively high energy barriers, which is in agreement with a relatively slow process. The precursor regeneration process is in all cases exergonic and it presents low energy barriers, particularly when compared to those of the activation process. This indicates that the precursor regeneration should always be feasible, unlike the moderate recoveries sometimes observed experimentally, which suggests that other competitive processes that hinder recovery should take place. Indeed, calculations presented in this work show that the reactions between the more abundant olefinic products and the active carbenes usually require lower energy barriers than those that regenerate the initial precatalyst, which could prevent precursor regeneration. On the other hand, varying the precursor concentration with time obtained from the computed energy barriers shows that, under the reaction conditions, the precursor activation is incomplete, thereby suggesting that the origin of the recovered catalyst probably arises from incomplete precursor activation. 相似文献
999.
1000.