全文获取类型
收费全文 | 4360篇 |
免费 | 113篇 |
国内免费 | 10篇 |
专业分类
化学 | 3310篇 |
晶体学 | 13篇 |
力学 | 53篇 |
综合类 | 1篇 |
数学 | 566篇 |
物理学 | 444篇 |
无线电 | 96篇 |
出版年
2021年 | 55篇 |
2020年 | 53篇 |
2019年 | 38篇 |
2018年 | 43篇 |
2017年 | 40篇 |
2016年 | 83篇 |
2015年 | 95篇 |
2014年 | 110篇 |
2013年 | 183篇 |
2012年 | 181篇 |
2011年 | 178篇 |
2010年 | 116篇 |
2009年 | 104篇 |
2008年 | 168篇 |
2007年 | 189篇 |
2006年 | 155篇 |
2005年 | 147篇 |
2004年 | 117篇 |
2003年 | 109篇 |
2002年 | 108篇 |
2001年 | 40篇 |
2000年 | 56篇 |
1999年 | 45篇 |
1998年 | 40篇 |
1997年 | 49篇 |
1996年 | 41篇 |
1995年 | 57篇 |
1994年 | 58篇 |
1993年 | 41篇 |
1992年 | 36篇 |
1991年 | 47篇 |
1990年 | 39篇 |
1989年 | 48篇 |
1988年 | 38篇 |
1987年 | 47篇 |
1986年 | 43篇 |
1985年 | 61篇 |
1984年 | 70篇 |
1983年 | 40篇 |
1982年 | 55篇 |
1981年 | 56篇 |
1980年 | 45篇 |
1979年 | 43篇 |
1978年 | 67篇 |
1977年 | 61篇 |
1976年 | 46篇 |
1975年 | 40篇 |
1974年 | 35篇 |
1973年 | 47篇 |
1971年 | 46篇 |
排序方式: 共有4483条查询结果,搜索用时 0 毫秒
1.
Central European Journal of Operations Research - This paper deals with the dynamic efficiency analysis based on Data Envelopment Analysis (DEA) models. Our aim is to formulate new dynamic DEA... 相似文献
2.
3.
Konstantinos Spyrou Matteo Calvaresi Evmorfia K. Diamanti Theodoros Tsoufis Dimitrios Gournis Petra Rudolf Francesco Zerbetto 《Advanced functional materials》2015,25(2):263-269
Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”. 相似文献
4.
Synthesis and Photophysical Properties of a Sc3N@C80‐Corrole Electron Donor–Acceptor Conjugate
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
5.
A protocol to correct for intra‐ and interspecific variation in tail hair growth to align isotope signatures of segmentally cut tail hair to a common time line
下载免费PDF全文
![点击此处可从《Rapid communications in mass spectrometry : RCM》网站下载免费的PDF全文](/ch/ext_images/free.gif)
6.
7.
Wolfram Bremser Roland Becker Heinrich Kipphardt Petra Lehnik-Habrink Ulrich Panne Antje Töpfer 《Accreditation and quality assurance》2006,11(10):489-495
ISO Guide 35 deals with RM stability issues and scrutinizes the evaluation of stability testing results under the assumption that either there is no trend at all (a rather rare situation), or any observed deterministic change is insignificant and thus can be neglected. However, market demands for reliable reference materials are obviously not limited to stable or at least seemingly stable materials. In many analytical applications, analytes and measurands under consideration are known, or at least suspected, to be unstable on time scales that may vary widely from measurand to measurand. The Federal Institute for Materials Research and Testing (BAM) has developed (and successfully uses) an integrated approach in its certification practice. The approach is based on an initial stability study and subsequent post-certification monitoring. Data evaluation is model-based and takes advantage of all information collected in the stability testing scheme(s). It thus allows one to deal with any kind of instability observed, to assess limiting time intervals at any stress condition in the range tested, to estimate a final expiry date for materials with detected instabilities or the maximum admissible re-testing interval for seemingly stable materials, and to assess maximum admissible stress loads during delivery of the material to the customer. The article describes (and exemplifies) typical study layout, the model selection, and the integrated data assessment. 相似文献
8.
P. Rudolf R. Raval P. Dumas G.P. Williams 《Applied Physics A: Materials Science & Processing》2002,75(1):147-153
Infrared (IR) spectroscopy of chemisorbed C60 on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency
shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm-1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C60/Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest
to be the frustrated translational mode of the adsorbed molecules.
Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering
of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction
coefficient of the C60 molecules, which results in rather small values (∼2×109 s-1 for Ag and Au, and ∼1.6×109 s-1for Cu), consistent with a marked metallic character of the adsorbed molecules.
Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C60 deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due
to strong electron–phonon coupling with induced surface states.
Received: 6 June 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002 相似文献
9.
Ohne Zusammenfassung 相似文献
10.