全文获取类型
收费全文 | 52887篇 |
免费 | 15995篇 |
国内免费 | 98篇 |
专业分类
化学 | 63011篇 |
晶体学 | 93篇 |
力学 | 1297篇 |
数学 | 2887篇 |
物理学 | 1692篇 |
出版年
2024年 | 428篇 |
2023年 | 4323篇 |
2022年 | 1829篇 |
2021年 | 2875篇 |
2020年 | 4904篇 |
2019年 | 2510篇 |
2018年 | 2616篇 |
2017年 | 804篇 |
2016年 | 5919篇 |
2015年 | 5874篇 |
2014年 | 5313篇 |
2013年 | 5820篇 |
2012年 | 3910篇 |
2011年 | 1945篇 |
2010年 | 3871篇 |
2009年 | 3801篇 |
2008年 | 1813篇 |
2007年 | 1495篇 |
2006年 | 815篇 |
2005年 | 722篇 |
2004年 | 600篇 |
2003年 | 510篇 |
2002年 | 460篇 |
2001年 | 195篇 |
2000年 | 154篇 |
1999年 | 132篇 |
1998年 | 130篇 |
1997年 | 144篇 |
1996年 | 181篇 |
1995年 | 197篇 |
1994年 | 157篇 |
1993年 | 264篇 |
1992年 | 128篇 |
1991年 | 139篇 |
1988年 | 144篇 |
1984年 | 149篇 |
1982年 | 140篇 |
1981年 | 142篇 |
1980年 | 161篇 |
1979年 | 143篇 |
1978年 | 150篇 |
1977年 | 197篇 |
1976年 | 212篇 |
1975年 | 209篇 |
1974年 | 209篇 |
1972年 | 155篇 |
1971年 | 132篇 |
1970年 | 213篇 |
1969年 | 132篇 |
1968年 | 140篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Maria Merces Marques C. Costa F. Lemos F. Ram?a Ribeiro A. R. Dias 《Reaction Kinetics and Catalysis Letters》1997,62(1):9-15
In this paper we present a kinetic approach to the analysis of steady-state homogeneous Ziegler-Natta polymerization activity
data. The influence of the number of monomeric species that are coordinated to the active site on the apparent rate law is
discussed and the equations are fitted to the experimental results. 相似文献
82.
Prof. G. Liptay 《Journal of Thermal Analysis and Calorimetry》1994,42(2-3):293-294
83.
Prof. Dr. A. Vassiliadis 《Colloid and polymer science》1970,242(1-2):1131-1141
Zusammenfassung Das Verhalten des Wollkeratins ist im kochenden Wasser nach Behandlung mit Kupfer-, Kadmium-, Silber- und Quecksilbersalzen unnormal, nicht nur verglichen mit dem Verhalten des metallfreien Proteins, sondern auch gegenüber des unter gleichen Bedingungen mit anderen Metallen behandelten Keratins. Die beobachteten Phänomene werden in einigen Fällen entweder mit der Annahme der Bildung von Vernetzungen zwischen benachbarten Polypeptidketten durch Komplexbildung des Metalls mit einigen Gruppen des Keratins oder durch Blockieren des Cysteins und der Verhinderung des Disulfidaustausches erklärt. In anderen Fällen jedoch, besonders bei Silber, ist die Erklärung der eintretenden Veränderung mit Hilfe dieser zwei Mechanismen nicht möglich, und es wird die direkte Reaktion des Metalls mit dem Schwefel des Cystins vorgeschlagen. Hierbei wird das Cystin und damit die Disulfidbindung gespalten. Die Spaltung dieser Bindung und die Verhinderung ihrer Rückbildung, entweder in derselben oder in anderer Lage, senkt die Zahl der Quervernetzungen im Keratin herab und damit die Fixierung der Polypeptidketten in ihrer ursprünglichen Lage. Hieraus resultiert eine Schrumpfung der Ketten und die Kontraktion der Faser.
Mit 10 Abbildungen und 2 Tabellen 相似文献
Summary Wool fibres containing cadmium, copper, mercury or silver set in a different way than the untreated ones or the fibres which contain other metals. This behaviour is explained in some cases by assuming the formation of complexes between the metal and the protein or by the disulphide exchange mechanism. In other cases, however, and particularly with silver this is not possible, and therefore the direct reaction between the metal and the sulphur of cystine is proposed. According to this mechanism the contraction of the fibre is due to the breakdown of the disulphide bond and the inability of its reformation.
Mit 10 Abbildungen und 2 Tabellen 相似文献
84.
Ghirardi Maria L. Togasaki Robert K. Seibert Michael 《Applied biochemistry and biotechnology》1997,63(1):141-151
Applied Biochemistry and Biotechnology - Photoproduction of H2 by green algae utilizes electrons originating from the photosynthetic oxidation of water and does not require metabolic intermediates.... 相似文献
85.
Abstract The photosensitizer riboflavin induces accumulation of the colorless flagellate Peridiniopsis berolinensis in a light field at low photon fluence rates but dispersal from a light field at high photon fluence rates. The wavelength dependence of the accumulation resembles the absorption spectrum of riboflavin in the visible range. The photodynamic effects are caused by a positive or negative chemotactic response to photoproducts in the medium which are produced by photochemical reactions of the dye. 相似文献
86.
The model of Onsager in which a polar molecule undergoes a reaction field due to the polarization of the molecular surroundings is used to evaluate by a S.C.F. calculation (CNDO/2 approximation) the modifications of a molecular structure in the liquid state.Application to water molecule and to three polar dimers for values of the dielectric constant varying between 3 and 78, shows that most of geometric parameters and dipoles moments vary of few per cent when the molecule is inserted in a liquid. In the liquid state dipole moments do not depend very much on the dielectric constant but energies and relative stabilities of isomers are strongly dependent on the medium.[/p] 相似文献
87.
Prof. Gerald B. Porter 《Theoretical chemistry accounts》1972,24(2-3):265-270
Analysis of the transient and steady-state kinetics of reversible energy transfer shows that while the interpretation of lifetime measurements is difficult unless the donor and acceptor lifetimes are appreciably different, quantum yield measurements are relatively easy to interpret.
Dedicated to the memory of Professor K. H. Hansen. 相似文献
Zusammenfassung Die Analyse der Kinetik der Übergangszustände und der stationären Zustände der reversiblen Energieübertragung zeigt, daß im Gegensatz zu einer schwierigen Interpretation der Messungen der Lebensdauer — es sei denn die Lebensdauer von Donor und Acceptor sind wesentlich voneinander verschieden — die Messungen der Quantumausbeute verhältnismäßig einfach zu interpretieren sind.
Résumé L'analyse de la cinétique de l'état transitoire et de l'état stationnaire du transfert réversible d'énergie montre que, si l'interprétation des mesures de durée de vie est difficile, à moins queles durées de vie du donneur et de l'accepteur soient très différentes, il est par contre relativement facile d'interpréter les mesures de rendement quantique.
Dedicated to the memory of Professor K. H. Hansen. 相似文献
88.
Michael Charwath Prof. Dr. Kurt Utvary Joseph M. Kanamueller 《Monatshefte für Chemie / Chemical Monthly》1977,108(5):1093-1097
Prolonged heating of (CH3NPF3)2 in a sealed tube at 120°C yields (CH3N)4P3F7 and PF5. Under the experimental conditions these compounds react to (CH3N)4P3F6
+PF6
–. Reaction of (CH3NPF3)2 in the presence of PF5 leads to a marked decrease in the formation of the ionic compound. The influence of the fluoride donating saltsMF (M=Li, Na, K, Cs) is investigated.
Mit 1 Abbildung
Früher: Alkyliminophosphorsäuretrihalogenide, 1. und 2. Mitt. 相似文献
Mit 1 Abbildung
Früher: Alkyliminophosphorsäuretrihalogenide, 1. und 2. Mitt. 相似文献
89.
An enzyme inhibition biosensor, developed in our laboratory and previously used for the analysis of compounds with anticholinesterase activity (e.g. physostigmine, neostigmine, pyridostigmine nicotine and organophosphorus compounds) has now been tested for the analysis of another recently synthesized cholinesterase inhibitor, i.e. eptastigmine. In addition nicotinic acid and nicotinamide, although displaying weaker inhibition properties, were also tested in pharmaceutical products using the same inhibition enzyme sensor. The biosensor consisted of a hydrogen peroxide amperometric electrode coupled to a functionalised nylon membrane chemically bonding both the enzymes butyrylcholinesterase and choline oxidase; a butyrylcholine standard solution in glycine buffer acted as substrate. The response of the system to all the inhibitors considered was characterised completely and the analysis of several pharmaceutical formulations containing nicotinamide or nicotinic acid was also performed. 相似文献
90.
The application of contact transformation theory to the perturbed harmonic oscillator is reexamined in the light of the harmonic oscillator tensors previously presented. It is found that the recasting of the formalism of this problem in terms of harmonic oscillator tensors results in great simplifications, most of which stem from the introduction of the additional algebraic quantum numbers (l, m). The order of magnitude of each fragment of the Hamiltonian is easily recognizable, and the diagonal and nondiagonal parts contained therein are readily identifiable. The determination of the contact transformation operator is reduced to a simple formula. First, an analysis is made for a single mode of vibration, and it is subsequently extended to a multimode case. The perturbed diatomic vibrator is presented as an example. 相似文献