全文获取类型
收费全文 | 1663篇 |
免费 | 87篇 |
国内免费 | 4篇 |
专业分类
化学 | 1287篇 |
晶体学 | 2篇 |
力学 | 41篇 |
数学 | 191篇 |
物理学 | 233篇 |
出版年
2023年 | 19篇 |
2022年 | 26篇 |
2021年 | 33篇 |
2020年 | 32篇 |
2019年 | 34篇 |
2018年 | 26篇 |
2017年 | 18篇 |
2016年 | 64篇 |
2015年 | 50篇 |
2014年 | 51篇 |
2013年 | 86篇 |
2012年 | 136篇 |
2011年 | 148篇 |
2010年 | 65篇 |
2009年 | 67篇 |
2008年 | 105篇 |
2007年 | 96篇 |
2006年 | 90篇 |
2005年 | 72篇 |
2004年 | 62篇 |
2003年 | 49篇 |
2002年 | 34篇 |
2001年 | 23篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1991年 | 9篇 |
1988年 | 6篇 |
1985年 | 6篇 |
1984年 | 13篇 |
1981年 | 10篇 |
1979年 | 7篇 |
1974年 | 5篇 |
1959年 | 7篇 |
1958年 | 5篇 |
1956年 | 7篇 |
1955年 | 6篇 |
1949年 | 5篇 |
1948年 | 21篇 |
1947年 | 10篇 |
1938年 | 6篇 |
1934年 | 8篇 |
1933年 | 7篇 |
1865年 | 5篇 |
1864年 | 5篇 |
排序方式: 共有1754条查询结果,搜索用时 31 毫秒
1.
Dr. Jordan Donat Mr. Patrick Dubourdeaux Dr. Martin Clémancey Dr. Julia Rendon Clara Gervasoni Mr. Morgan Barbier Jessica Barilone Dr. Jacques Pécaut Prof. Dr. Serge Gambarelli Prof. Dr. Pascale Maldivi Prof. Dr. Jean-Marc Latour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202201875
Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two-electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor. 相似文献
2.
Guizellini Filipe Corrêa Franzin Bruno Trevizan da Silva Matheus Antonio Abra Luciana Mazotti Hojo Ossamu Pastre Iêda Aparecida Ribeiro Clóvis Augusto Paiva-Santos Carlos de Oliveira Fertonani Fernando Luis 《Journal of Thermal Analysis and Calorimetry》2021,143(1):47-60
Journal of Thermal Analysis and Calorimetry - The aim of this work is to synthesize and characterize a new structured silver–clay dried, calcined or sintered at different temperatures... 相似文献
3.
4.
Clément Gallo 《Comptes Rendus Mathematique》2006,342(5):319-323
We give an upper bound on the growth rate of the Schrödinger group on Zhidkov spaces. In dimension 1, we prove that this bound is sharp. To cite this article: C. Gallo, C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
5.
6.
A time-dependent model corresponding to an Oldroyd-B viscoelastic fluid is considered, the convective terms being disregarded.
Global existence in time is proved in Banach spaces provided the data are small enough, using the implicit function theorem
and a maximum regularity property for a three fields Stokes problem. A finite element discretization in space is then proposed.
Existence of the numerical solution is proved for small data, so as a priori error estimates, using again an implicit function
theorem.
Supported by the Swiss National Science Foundation. Fellowship PBEL2–114311. 相似文献
7.
This paper presents a method to estimate reflected and transmitted wave amplitude spectra in a bounded domain such as a wave tank, when available data signals must be shortened due to interferences and wall effects. This paper extends the well known Goda and Suzuki two-probe method to three probes. The paper also suggests solutions to compute reliable transmission and reflection coefficients in spite of problems linked to higher harmonics and to the interference between different wave trains propagating in the tank. To cite this article: G. Duclos, A.H. Clément, C. R. Mecanique 331 (2003). 相似文献
8.
Sannomiya M Rodrigues CM Coelho RG dos Santos LC Hiruma-Lima CA Souza Brito AR Vilegas W 《Journal of chromatography. A》2004,1035(1):47-51
The methanolic extract of the leaves of the medicinal plant Byrsonima crassa (Malpighiaceae) contain flavonoids with antioxidant activity. They were separated in a preparative scale using high-speed counter-current chromatography. The optimum solvent system used was composed of a mixture of ethyl acetate-n-propanol-water (140:8:80 (v/v/v)) and led to a successful separation between monoglucosilated flavonoids (quercetin-3-O-alpha-L-arabinoside, quercetin-3-O-beta-D-galactoside) and the biflavonoid amentoflavone in only 3.5 h. The purities of quercetin-3-O-alpha-L-arabinoside (95 mg), quercetin-3-O-beta-D-galactoside (16 mg) and the biflavonoid amentoflavone (114 mg) were all isolated at purity over 95%. Identification was performed by 1H NMR, 13C NMR and UV analyses. 相似文献
9.
Résumé La méthyl-9-trihydroxy-2,3,7-fluorone-6 permet de déceler les ions de l'antimoine, en présence de tous autres cations et anions. Les conditions deph (ph = 4) sont à observer rigoureusement.Ce nouveau réactif est avantageusement utilisé dans la méthode d'analyse à la touche ou par empreinte.Les limites de sensibilité sont: en godet 0,2; sur papier gélatine 0,5; sur papier filtre 0,8.
Summary Methyl-9-trihydroxy-2,3,7-fluorone-6 is a reagent which allows to detect antimony ion in the presence of all the other cations and anions. Aph value of 4 must be strictly maintained.This new reagent can be advantageously applied for spot test and offprint analysis.Limits of identification: On the spot test plate 0,2; On gelatine paper 0,5; On filter paper 0,8.
Zusammenfassung Das Methyl-9-trioxy-2,3,7-fluoron-6 gestattet den Nachweis des Antimonions in Gegenwart aller anderen Kationen und Anionen. Dieph-Bedingungen (ph = 4) sind streng einzuhalten.Dieses neue Reagens läßt sich mit Vorteil zur Tüpfel- oder Abdruckanalyse verwenden.Erfassungsgrenzen: auf der Tüpfelplatte 0,2; auf Gelatinepapier 0,5; auf Filtrierpapier 0,8.相似文献
10.
Moraes ML Bonardi C Mendonça CR Campana PT Lottersberger J Tonarelli G Oliveira ON Beltramini LM 《Colloids and surfaces. B, Biointerfaces》2005,41(1):15-20
The study of interactions between biological molecules and model membranes is essential for the understanding of a number of physiological mechanisms involved in viral infections and dissemination. In this paper, the analysis of the interaction between a peptide from the p24 protein of Human Immunodeficiency Virus type 1 (HIV-1) and a phospholipid monolayer has pointed to a cooperative response in which very small amounts of peptide p24-1 (e.g. 0.05 mol%) can lead to measurable effects. Monolayer surface pressure and surface potential isotherms were affected for peptide concentrations as low as 0.05 mol%, with saturation at 0.5 mol%. The expansion effect from p24-1 is confirmed by changes in morphology of the monolayers using Brewster angle microscopy. Even though p24-1 is disordered in aqueous solutions, the interaction with dipalmitoyl phosphatidylcholine (DPPC) causes it to adopt an alpha-helix structure, as shown by circular dichroism (CD) data for multilamellar vesicles (MLV). The expansion of the phospholipid monolayer in a cooperative way may imply that p24-1 has potential antiviral activity, by participating in the cell rupture, with no need of specific receptors in the membrane. 相似文献