全文获取类型
收费全文 | 5232篇 |
免费 | 244篇 |
国内免费 | 35篇 |
专业分类
化学 | 3759篇 |
晶体学 | 19篇 |
力学 | 131篇 |
数学 | 903篇 |
物理学 | 699篇 |
出版年
2023年 | 41篇 |
2022年 | 41篇 |
2021年 | 95篇 |
2020年 | 117篇 |
2019年 | 115篇 |
2018年 | 74篇 |
2017年 | 58篇 |
2016年 | 159篇 |
2015年 | 146篇 |
2014年 | 181篇 |
2013年 | 285篇 |
2012年 | 315篇 |
2011年 | 371篇 |
2010年 | 262篇 |
2009年 | 210篇 |
2008年 | 326篇 |
2007年 | 331篇 |
2006年 | 318篇 |
2005年 | 319篇 |
2004年 | 248篇 |
2003年 | 213篇 |
2002年 | 223篇 |
2001年 | 95篇 |
2000年 | 76篇 |
1999年 | 74篇 |
1998年 | 61篇 |
1997年 | 68篇 |
1996年 | 72篇 |
1995年 | 45篇 |
1994年 | 43篇 |
1993年 | 28篇 |
1992年 | 26篇 |
1991年 | 33篇 |
1990年 | 23篇 |
1989年 | 32篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 33篇 |
1983年 | 27篇 |
1982年 | 33篇 |
1981年 | 23篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1978年 | 33篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 19篇 |
排序方式: 共有5511条查询结果,搜索用时 546 毫秒
1.
2.
3.
Synthesis and Photophysical Properties of a Sc3N@C80‐Corrole Electron Donor–Acceptor Conjugate 下载免费PDF全文
Bin Liu Hongyun Fang Prof. Xiaofang Li Wenting Cai Lipiao Bao Marc Rudolf Fabian Plass Prof. Louzhen Fan Prof. Xing Lu Prof. Dirk M. Guldi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):746-752
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics. 相似文献
4.
5.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
6.
Jonathan M. Levin Lawrence L. Wald Marc J. Kaufman Marjorie H. Ross Luis C. Maas Perry F. Renshaw 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):292-295
Residual effects of an initial bolus of gadolinium contrast agent have been previously demonstrated in sequential dynamic susceptibility contrast MR experiments. While these residual effects quickly reach a saturation steady state, their etiology is uncertain, and they can lead to spurious estimates of hemodynamic parameters in activation experiments. The possible influence ofT1effects is now investigated with experiments in whichT1weighting is varied as well as with serial regionalT1measurements. Little evidence for significant residualT1effects is found, suggesting instead that susceptibility effects underlie these observations. An initial saturation dose of contrast agent minimizes this effect. 相似文献
7.
The values of the Higgs mass are obtained for two possibilities of extending the standard model in a way compatible with the existence of a noncommutative structure at high energies. We assume the existence of a big desert between the low energy electroweak scale and the high energy scale Λ=1.1×1017 GeV, where noncommutative features become relevant. We conclude that it is extremely difficult to depart from the Higgs mass value obtained from noncommutative geometry for the standard model with three generations only. 相似文献
8.
J. Mlynár J. Ongena The EFDA JET Contributions I. Duran M. Hron R. Pánek V. Petržílka F. Žáček 《Czechoslovak Journal of Physics》2004,54(3):C28
JET (Joint European Torus) is the largest tokamak in the world and the only fusion facility able to operate with Tritium, the fusion fuel, and Beryllium, the ITER first wall material. JET also features the most complete remote handling equipment for invessel maintenance. As a multinational research center, JET provides logistic experience in preparing for operation of the global facility, tokamak ITER.Experiments on JET are focused on ITER-relevant studies, in particular on detailing the operational scenarios (EL My H-modes and advanced regimes), on enhancing the heating systems, on developing diagnostics for burning plasmas etc. Pioneering real-time control techniques have been implemented that maximize performance and minimize internal disturbances of JET plasmas. In helium plasmas, ion cyclotron heating (ICRH) created fast α-particles, mimicking their populations in future burning plasmas. The recent successful Trace Tritium campaign provided important new data on fuel transport. Current enhancements on JET include a new ITER-like ELM-resilient high power ICRH antenna (7 MW) and over twenty new diagnostics that will further extend the JET scientific capabilities and push the facility even closer to the ITER parameters.A special mention is given to the involvement of the fusion experts from Association EURATOM-IPP.CR, who have been actively participating in the collective use of JET facility for more than three years. 相似文献
9.
10.
A Variable Neighborhood Search for the Multi Depot Vehicle Routing Problem with Time Windows 总被引:6,自引:0,他引:6
Michael Polacek Richard F. Hartl Karl Doerner Marc Reimann 《Journal of Heuristics》2004,10(6):613-627
The aim of this paper is to propose an algorithm based on the philosophy of the Variable Neighborhood Search (VNS) to solve Multi Depot Vehicle Routing Problems with Time Windows. The paper has two main contributions. First, from a technical point of view, it presents the first application of a VNS for this problem and several design issues of VNS algorithms are discussed. Second, from a problem oriented point of view the computational results show that the approach is competitive with an existing Tabu Search algorithm with respect to both solution quality and computation times. 相似文献