全文获取类型
收费全文 | 31062篇 |
免费 | 413篇 |
国内免费 | 28篇 |
专业分类
化学 | 25652篇 |
晶体学 | 75篇 |
力学 | 224篇 |
综合类 | 1篇 |
数学 | 2309篇 |
物理学 | 3242篇 |
出版年
2016年 | 312篇 |
2015年 | 269篇 |
2014年 | 263篇 |
2013年 | 572篇 |
2012年 | 536篇 |
2011年 | 673篇 |
2010年 | 366篇 |
2009年 | 347篇 |
2008年 | 579篇 |
2007年 | 593篇 |
2006年 | 517篇 |
2005年 | 558篇 |
2004年 | 466篇 |
2003年 | 412篇 |
2002年 | 340篇 |
2001年 | 249篇 |
1997年 | 238篇 |
1996年 | 241篇 |
1995年 | 258篇 |
1993年 | 245篇 |
1988年 | 291篇 |
1987年 | 326篇 |
1986年 | 310篇 |
1985年 | 426篇 |
1984年 | 413篇 |
1982年 | 355篇 |
1981年 | 299篇 |
1980年 | 515篇 |
1979年 | 418篇 |
1978年 | 1244篇 |
1977年 | 998篇 |
1976年 | 408篇 |
1975年 | 276篇 |
1974年 | 264篇 |
1973年 | 276篇 |
1968年 | 282篇 |
1967年 | 266篇 |
1966年 | 297篇 |
1965年 | 320篇 |
1964年 | 296篇 |
1962年 | 426篇 |
1961年 | 320篇 |
1960年 | 416篇 |
1959年 | 323篇 |
1958年 | 335篇 |
1956年 | 290篇 |
1955年 | 255篇 |
1937年 | 251篇 |
1935年 | 250篇 |
1933年 | 274篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
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
3.
Pu Duan Bo Zhi Luke Coburn Christy L. Haynes Klaus Schmidt-Rohr 《Magnetic resonance in chemistry : MRC》2020,58(11):1130-1138
The composition of fluorescent polymer nanoparticles, commonly referred to as carbon dots, synthesized by microwave-assisted reaction of citric acid and ethylenediamine was investigated by 13C, 13C{1H}, 1H─13C, 13C{14N}, and 15N solid-state nuclear magnetic resonance (NMR) experiments. 13C NMR with spectral editing provided no evidence for significant condensed aromatic or diamondoid carbon phases. 15N NMR showed that the nanoparticle matrix has been polymerized by amide and some imide formation. Five small, resolved 13C NMR peaks, including an unusual ═CH signal at 84 ppm (1H chemical shift of 5.8 ppm) and ═CN2 at 155 ppm, and two distinctive 15N NMR resonances near 80 and 160 ppm proved the presence of 5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA) or its derivatives. This molecular fluorophore with conjugated double bonds, formed by a double cyclization reaction of citric acid and ethylenediamine as first shown by Y. Song, B. Yang, and coworkers in 2015, accounts for the fluorescence of the carbon dots. Cross-peaks in a 1H─13C HETCOR spectrum with brief 1H spin diffusion proved that IPCA is finely dispersed in the polyamide matrix. From quantitative 13C and 15N NMR spectra, a high concentration (18 ± 2 wt%) of IPCA in the carbon dots was determined. A pronounced gradient in 13C chemical-shift perturbations and peak widths, with the broadest lines near the COO group of IPCA, indicated at least partial transformation of the carboxylic acid of IPCA by amide or ester formation. 相似文献
4.
5.
6.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
7.
Let R be a discrete nonsingular equivalence relation on a standard probability space , and let V be an ergodic strongly asymptotically central automorphism of R. We prove that every V-invariant cocycle with values in a Polish group G takes values in an abelian subgroup of G.
The hypotheses of this result are satisfied, for example, if A is a finite set, a closed, shift-invariant subset, V is the shift, μ a shift-invariant and ergodic probability measure on X, the two-sided tail-equivalence relation on X, a shift-invariant subrelation which is μ-nonsingular, and a shift-invariant cocycle. 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.
Ohne Zusammenfassung 相似文献