全文获取类型
收费全文 | 1122篇 |
免费 | 23篇 |
国内免费 | 6篇 |
专业分类
化学 | 756篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 96篇 |
物理学 | 272篇 |
出版年
2021年 | 10篇 |
2019年 | 12篇 |
2018年 | 11篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 22篇 |
2014年 | 14篇 |
2013年 | 36篇 |
2012年 | 33篇 |
2011年 | 42篇 |
2010年 | 31篇 |
2009年 | 27篇 |
2008年 | 46篇 |
2007年 | 49篇 |
2006年 | 33篇 |
2005年 | 40篇 |
2004年 | 29篇 |
2003年 | 36篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 29篇 |
1999年 | 20篇 |
1998年 | 22篇 |
1997年 | 22篇 |
1996年 | 33篇 |
1995年 | 32篇 |
1994年 | 20篇 |
1993年 | 24篇 |
1992年 | 27篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 24篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 19篇 |
1974年 | 13篇 |
1972年 | 11篇 |
1969年 | 14篇 |
1968年 | 12篇 |
1967年 | 13篇 |
排序方式: 共有1151条查询结果,搜索用时 15 毫秒
1.
2.
We clarify the way in which cosmological perturbations of quantum origin, produced during inflation, assume classical properties. Two features play an important role in this process: First, the dynamics of fluctuations which are presently on large cosmological scales leads to a very peculiar state (highly squeezed) that is indistinguishable, in a precise sense, from a classical stochastic process. This holds for almost all initial quantum states. Second, the process of decoherence by interaction with the environment distinguishes the field amplitude basis as the robust pointer basis. We discuss in detail the interplay between these features and use simple analogies such as the free quantum particle to illustrate the main conceptual issues. 相似文献
3.
M. Trunk J. Popp I. Hartmann M. Lankers E. Urlaub W. Kiefer 《Fresenius' Journal of Analytical Chemistry》1996,355(3-4):354-356
In situ measurements of gas-liquid surface reactions of single aerosol microdroplets are presented. By means of optical levitation in combination with elastic (Mie) and inelastic (Raman) light scattering it is possible to get information on the chemistry of e.g. acid/base reactions as well as the physical behavior of single microparticles. 相似文献
4.
5.
H. Falk R. Geerling B. Hattendorf K. Krengel-Rothensee K. P. Schmidt 《Analytical and bioanalytical chemistry》1997,359(4-5):352-356
An ICP-MS method for the determination of ultra-traces of 24 Elements (Li, Be, Mg, Al, Cr, Mn, Co, Zn, Cu, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, Sn, Sb, Ba, Tl, Pb, Bi, U) at ng/L to μg/L levels in highly saline solutions (up to 30 g/L NaCl) was developed. Calculated to the salt content of the samples, limits of detection at the sub-μg/kg level were obtained. This allows the measurement of samples like sea water, or clinical samples like urine, serum and whole blood, with few or without sample preparation and a drastic improvement to the limits of detection. Compared to the determination in solutions of 1 g/L NaCl the limits of detection in the original sample were improved by one order of magnitude. Improvements in instrumental stability are achieved by the use of an additional gas, that is introduced to the aerosol stream and avoids salt deposition in the aerosol tube of the torch, the use of High Matrix Content (HMC) cones, that show no clogging even at NaCl-concentrations up to 50 g/L. With this setup the long term stability for measurements with changing matrix concentrations is < 10% without and < 5% with use of an internal standard for the individual samples. Cleaning up is necessary after 2 days of operation. The direct analysis of the Nearshore Seawater Reference Material NRC-CNRC CASS3 showed a good agreement with the certified and measured concentrations. Elements, that do not suffer from an isobaric overlap of matrix compounds can be determined clearly at ng/L levels. Measurement of different matrix concentrations showed, that acceptable results can be achieved with a single calibration for concentrations from 5 g/L NaCl to 30 g/L NaCl, though matrix matching shows the best results. 相似文献
6.
7.
Benjamin Falk Santiago M. Vallinas James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2003,41(4):579-596
This article describes the development of optical pyrometry (OP) as a new analytical technique for the continuous monitoring of the progress of both free‐radical and cationic photopolymerizations. The method is rapid, reproducible, and very easy to implement. A temperature profile of a photopolymerization can be obtained. Preliminary studies have shown that the temperatures of some polymerizing monomers can easily reach temperatures in excess of 250 °C. The effects of the mass and reactivity of the monomer, light intensity, structures, and concentrations of the photoinitiators and monomers as well as the presence or absence of oxygen on various free‐radical and cationic photopolymerizations were examined with this method. Coupling of real‐time infrared spectroscopy with OP provides a convenient method for simultaneously monitoring both the chemical conversion and the temperature of a photopolymerization. This combined technique affords new insights into the effects of temperature‐induced autoacceleration on the course of photopolymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 579–596, 2003 相似文献
8.
9.
Summary N-Arylsubstituted ureas undergo exchange of the N-residue upon reaction with amines. Using kinetic measurements, investigation of product distribution, regioselectivity, catalysis, and substrate influences, it was shown that this reaction proceeds via a second order nucleophilic substitution at the urea carbonyl center. By means of semiempirical calculations using the MNDO method the alternative mechanism of fragmentation was investigated.
Zur Synthese N-substituierter Harnstoffe II: Nucleophile Substitution von Harnstoffen an der Carbonylgruppe
Zusammenfassung N-Arylsubstituierte Harnstoffe erleiden bei der Reaktion mit Aminen einen Austausch des N-Restes. Durch kinetische Messungen, Untersuchung der Produktverteilung, Regioselektivität, Katalyse und des Einflusses des Edukts konnte abgeleitet werden, daß es sich hiebei um eine nucleophile Substitution zweiter Ordnung am Carbonylzentrum des Harnstoffs handelt. Durch semiempirische Rechnungen mit Hilfe der MNDO Methode wurde der alternative Reaktionsmechanismus einer Fragmentierung untersucht.相似文献
10.