全文获取类型
收费全文 | 48447篇 |
免费 | 1968篇 |
国内免费 | 18篇 |
专业分类
化学 | 31312篇 |
晶体学 | 232篇 |
力学 | 1564篇 |
数学 | 7472篇 |
物理学 | 9853篇 |
出版年
2023年 | 375篇 |
2022年 | 294篇 |
2021年 | 492篇 |
2020年 | 670篇 |
2019年 | 631篇 |
2018年 | 1000篇 |
2017年 | 812篇 |
2016年 | 1519篇 |
2015年 | 1394篇 |
2014年 | 1394篇 |
2013年 | 2879篇 |
2012年 | 3376篇 |
2011年 | 3437篇 |
2010年 | 2060篇 |
2009年 | 1686篇 |
2008年 | 2952篇 |
2007年 | 2968篇 |
2006年 | 2614篇 |
2005年 | 2538篇 |
2004年 | 2182篇 |
2003年 | 1762篇 |
2002年 | 1534篇 |
2001年 | 905篇 |
2000年 | 759篇 |
1999年 | 538篇 |
1998年 | 405篇 |
1997年 | 364篇 |
1996年 | 466篇 |
1995年 | 294篇 |
1994年 | 347篇 |
1993年 | 351篇 |
1992年 | 377篇 |
1991年 | 326篇 |
1990年 | 312篇 |
1989年 | 307篇 |
1988年 | 248篇 |
1987年 | 250篇 |
1986年 | 219篇 |
1985年 | 378篇 |
1984年 | 346篇 |
1983年 | 236篇 |
1982年 | 326篇 |
1981年 | 312篇 |
1980年 | 273篇 |
1979年 | 267篇 |
1978年 | 249篇 |
1976年 | 263篇 |
1975年 | 239篇 |
1974年 | 247篇 |
1973年 | 238篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
961.
Pandya SU Garçon C Chavant PY Py S Vallée Y 《Chemical communications (Cambridge, England)》2001,(18):1806-1807
The vinylzinc reagents derived from hydrozirconation of alkynes and transmetallation add readily to nitrones to yield pure (E)-N-allylhydroxylamines; some of these rearrange into O-allylhydroxylamines. 相似文献
962.
Jean-Pierre Labbé 《Mikrochimica acta》1964,52(2-4):298-316
Résumé L'auteur reprend et complète la méthode de dosage microgravimétrique du germanium à l'état de germanimolybdate de tétraphénylarsonium (F
Ge=0,02137). Dans une deuxième partie, il décrit une méthode de préparation des heptagermanates alcalins et de métagermanates de métaux bivalents à partir des solutions d'oxyde GeO2 et d'acétates métalliques. Les courbes de thermolyse et les spectres d'absorption infrarouge sont présentés. Aucun orthogermanate ne précipite des solutions aqueuses.
Mémoire en l'honneur du professeurA. A. Benedetti-Pichler. 相似文献
Summary The author resumes and completes the method for the microgravimetric determination of germanium as the germanium molybdate of tetraphenylarsonium (F Ge=0.02137). In a second part he describes a method for preparing some heptagermanates of divalent metals from solutions of the oxide GeO2 and metal acetates. The thermolysis curves and the infrared absorption curves are given. No orthogermanate precipitates from aqueous solutions.
Zusammenfassung Der Verfasser berichtet über die mikrogravimetrische Bestimmung des Germaniums als Tetraphenylarsonium-Germanium-Molybdat (F Ge=0,02137). Im zweiten Teil der Arbeit wird die Herstellung von Alkaliheptagermanat sowie von Metagermanaten bivalenter Metalle aus Germaniumoxidlösungen und Metallacetaten beschrieben. Die Thermolysekurven und IR-Absorptionsspektren werden vorgelegt. Aus wäßrigen Lösungen fällt kein Orthogermanat aus.
Mémoire en l'honneur du professeurA. A. Benedetti-Pichler. 相似文献
963.
Treatment of 2-methylphenols with chloro(diphenyl)-lambda(3)-iodane led to their regioselective dearomatizing 2-phenylation into cyclohexa-2,4-dienone derivatives via a proposed ligand coupling reaction. In the same vein of investigation, treatment of 2-methylanilines with the lambda(5)-iodane 2-iodoxybenzoic acid IBX reagent led to their regioselective dearomatization into previously undescribed ortho-quinol imines. 相似文献
964.
Céline Pascal Claude Merlet Rose-Marie Marin-Ayral Jean-Claude Tedenac Bernard Boyer 《Mikrochimica acta》2004,145(1-4):147-151
The phases formed at the interface between an intermetallic (NiAl) and a nickel base superalloy joined by combustion synthesis were investigated, particularly the eutectic phases. Owing to their small size, the characterisation of these phases using a Castaings electron microprobe encounters difficulties. The analysis volume size is generally too large to differentiate the phases from their surrounding matrix, even by using low accelerating voltage. Moreover, the eutectic phases contain boron, which is difficult to characterise by EPMA. Independently of the phases shape, the characterisation can be solved by viewing this complex system as a surrounding matrix and a multi layer system. The results of these simulations revealed the presence of two categories of borides: the eutectic boride MM2B2 (M=Mo and M=Co, Cr) and the solid solution boride [Cr1–x (Mo, W)x]B. 相似文献
965.
A multiresidue, automated and rapid method for the determination of pesticide residues in olive oil is presented. The method employs the through oven transfer adsorption-desorption interface for the on-line coupling of reversed-phase liquid chromatography and gas chromatography. In this fully automated system, olive oil is directly injected with no sample pre-treatment step other than filtration. Methanol-water is used as eluent in the liquid chromatography pre-separation step. The selected liquid chromatography fraction containing the pesticides is automatically transferred to the gas chromatography. The liquid chromatography column flow during elution is different from the flow during the transfer. Using a flame ionisation detector, pesticide detection limits varied from 0.1 to 0.3 mg/l. 相似文献
966.
Gutiérrez MC Sleegers A Simpson HD Alphand V Furstoss R 《Organic & biomolecular chemistry》2003,1(20):3500-3506
The first fluorogenic assay allowing for detection of microbial enzymes able to perform Baeyer-Villiger oxidation is described. This is based on the use of 4-oxopentyl umbelliferyl ether 1 as a fluorogenic substrate. When Baeyer-Villigerases active against this test ketone are present in the selected whole cells, 1 is transformed into 3-hydroxypropyl umbelliferyl ether 3, which, in a subsequent step, releases the fluorescent product umbelliferone. Different microorganisms, known to be endowed with Baeyer-Villigerase activity, were assayed. 相似文献
967.
The new complex [Pd[t-Bu2PCH2N(CH2Ph)CH2P t-Bu2](OAc)2] is a very efficient catalyst for the Sonogashira cross-coupling reaction of aryl halides with acetylenes at room temperature, without co-catalyst. 相似文献
968.
Martí S Andrés J Moliner V Silla E Tuñón I Bertrán J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(4):984-991
In this paper a deeper insight into the chorismate-to prephenate-rearrangement, catalyzed by Bacillus subtilis chorismate mutase, is provided by means of a combination of statistical quantum mechanics/molecular mechanics simulation methods and hybrid potential energy surface exploration techniques. The main aim of this work is to present an estimation of the preorganization and reorganization terms of the enzyme catalytic rate enhancement. To analyze the first of these, we have studied different conformational equilibria of chorismate in aqueous solution and in the enzyme active site. Our conclusion is that chorismate mutase preferentially binds the reactive conformer of the substrate--that presenting a structure similar to the transition state of the reaction to be catalyzed--with shorter distances between the carbon atoms to be bonded and more diaxial character. With respect to the reorganization effect, an energy decomposition analysis of the potential energies of the reactive reactant and of the reaction transition state in aqueous solution and in the enzyme shows that the enzyme structure is better adapted to the transition structure. This means not only a more negative electrostatic interaction energy with the transition state but also a low enzyme deformation contribution to the energy barrier. Our calculations reveal that the structure of the enzyme is responsible for stabilizing the transition state structure of the reaction, with concomitant selection of the reactive form of the reactants. This is, the same enzymatic pattern that stabilizes the transition structure also promotes those reactant structures closer to the transition structure (i.e., the reactive reactants). In fact, both reorganization and preorganization effects have to be considered as the two faces of the same coin, having a common origin in the effect of the enzyme structure on the energy surface of the substrate. 相似文献
969.
Durry G Amarouche N Zéninari V Parvitte B Lebarbu T Ovarlez J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(14):805-3379
Since 1997, two near-infrared laser diode sensors have been developed with the support of the CNES, the French space agency, to provide in situ data of H(2)O, CH(4) and CO(2) in the middle atmosphere. The realized instruments were flown from stratospheric balloons within the framework of European campaigns for the study of stratospheric ozone and water vapor and were involved in the validation of the ODIN and ENVISAT satellites. In this paper, we describe the developed laser probing technique, we report atmospheric measurements and finally we discuss future perspectives, particularly the in situ laser sensing of the lower atmosphere of Mars and the implication of the laser hygrometers in balloon campaigns at mid-latitudes and tropical regions to investigate the sources and sinks of stratospheric H(2)O. 相似文献
970.
A new method is presented to calculate binding energies and eigenfunctions for molecules, using the relativistic Dirac hamiltonian. A numerical basis set of four component wavefunctions is obtained from atom-like Dirac-Slater wavefunctions. A discrete variational method has been developed and applied to the linear XeF2 molecule. 相似文献