全文获取类型
收费全文 | 460篇 |
免费 | 37篇 |
国内免费 | 1篇 |
专业分类
化学 | 359篇 |
晶体学 | 25篇 |
力学 | 4篇 |
数学 | 52篇 |
物理学 | 58篇 |
出版年
2023年 | 6篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2019年 | 14篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 15篇 |
2015年 | 23篇 |
2014年 | 20篇 |
2013年 | 36篇 |
2012年 | 44篇 |
2011年 | 43篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 33篇 |
2007年 | 29篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有498条查询结果,搜索用时 203 毫秒
41.
Rubén Marín-Barrios Francisco M. Guerra Ana Leticia García-Cabeza F. Javier Moreno-Dorado Guillermo M. Massanet 《Tetrahedron》2012,68(4):1105-1108
The multivariate optimization method known as simplex is applied to the Kharasch–Sosnovsky allylic oxidation of double bonds. By applying this method, the amounts of three variables (copper source, oxidant, and additive) are optimized at the same time. Under the conditions thus obtained the reaction takes place in a considerable shorter time, being the alkene the limiting reagent. These conditions are applied to some monoterpenes and sesquiterpenes leading regioselectively to the corresponding benzoate esters, opening a route to the employment of this reaction in the synthesis of more complex molecules. 相似文献
42.
We show that the entropy of a system constituted by a massive Schwarzschild black hole in stable thermal equilibrium with black body radiation is superadditive in Landsberg's sense. Furthermore, we comment on some consequences arising from the negative character of the heat capacity of that system. 相似文献
43.
Direct On‐Surface Patterning of a Crystalline Laminar Covalent Organic Framework Synthesized at Room Temperature 下载免费PDF全文
Alejandro de la Peña Ruigómez David Rodríguez‐San‐Miguel Dr. Kyriakos C. Stylianou Dr. Massimiliano Cavallini Dr. Denis Gentili Dr. Fabiola Liscio Prof. Silvia Milita Dr. Otello Maria Roscioni Dr. Maria Luisa Ruiz‐González Carlos Carbonell Prof. Daniel Maspoch Dr. Rubén Mas‐Ballesté Dr. José Luis Segura Dr. Félix Zamora 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10666-10670
We report herein an efficient, fast, and simple synthesis of an imine‐based covalent organic framework (COF) at room temperature (hereafter, RT‐COF‐1 ). RT‐COF‐1 shows a layered hexagonal structure exhibiting channels, is robust, and is porous to N2 and CO2. The room‐temperature synthesis has enabled us to fabricate and position low‐cost micro‐ and submicropatterns of RT‐COF‐1 on several surfaces, including solid SiO2 substrates and flexible acetate paper, by using lithographically controlled wetting and conventional ink‐jet printing. 相似文献
44.
Zinc‐Catalyzed Functionalization of SiH Bonds with 2‐Furyl Carbenoids through Three‐Component Coupling 下载免费PDF全文
Sergio Mata Dr. Luis A. López Dr. Rubén Vicente 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):8998-9002
A three‐component coupling of alk‐2‐ynals, 1,3‐dicarbonyls and silanes is reported. ZnCl2 serves as an inexpensive and low‐toxic catalyst for the overall transformation, which involves Knoevenagel condensation, cyclization, and carbene Si?H bond insertion. The process takes place with high atom economy in the absence of organic solvents and shows a broad scope. This reaction is also applicable to the functionalization of oligomeric siloxanes. 相似文献
45.
46.
Flavia?Colonna Rubén?A.?Martínez-Avenda?oEmail author 《Mediterranean Journal of Mathematics》2017,14(1):18
In this paper, we expand the study of the multiplication operators on the Lipschitz space of a tree begun in Colonna and Easley (Integral Equ Oper Theory 68:391–411, 2010) by focusing on their adjoint acting on a certain separable subspace of the Lipschitz space whose dual is isometrically isomorphic to \(\mathbf L^1\). We then study the properties of two useful operators \(\nabla \) and \(\Delta \) and use them (along with the multiplicative symbol \(\psi \)) to define the Toeplitz operator \(T_\psi \) on the space \(\mathbf L^p\) for \(1\le p \le \infty \). We give conditions for its boundedness and study its point spectrum. 相似文献
47.
Anish Khan Aftab Aslam Parwaz Khan Abdullah M. Asiri Malik Abdul Rub Mohammed M. Rahman Sulaiman Ab. Ghani 《Mikrochimica acta》2014,181(9-10):1049-1057
A composite was prepared from copper and graphene oxide (Cu-GO) by in-situ chemical reduction of a mixture containing GO and Cu(II) ions with potassium borohydride. The morphology and structure of the composite were confirmed by various physicochemical techniques. The materials were used in a tyrosinase-based microbiosensor where the enzyme is immobilized in a biocompatible matrix consisting of poly(ortho-phenylene diamine) and Cu-GO. The composite was deposited on the surface of an 8-μm thick carbon fiber microelectrode. The role of each component in the sensing layer was systematically investigated with respect to the analytical performance of the system. In its optimal configuration, the biosensor demonstrated (a) a sensitivity of 6.1?±?3 nA mM-1 dopamine (DA), (b) a linear response to DA (with a Michaelis-Menten constant of 0.29?±?0.03 mM), (c) good selectivity over ascorbic acid and uric acid, and (d) a high blocking capacity (112.2?±?2 mM) for ascorbic acid. Figure
Poly(o-phenylenediamine) electropolymerized carbon fiber electrode with sensitivity towards dopamine (DA) is 6.1?±?3 nA mM?1 supported by Cu-GO. The linear range for DA is 0.29?±?0.03 mM with 0.033 μM LOD and fast response time of <8 s with ascorbic acid blocking capacity of 112.2?±?2 mM AA. Studies on different ratio of Glu/Tyr revealed that 10:3 gave best overall response. 相似文献
48.
Cormanich RA Moreira MA Freitas MP Ramalho TC Anconi CP Rittner R Contreras RH Tormena CF 《Magnetic resonance in chemistry : MRC》2011,49(12):763-767
The present study shows that a hydrogen bond between the OH group and the fluorine atom is not involved in the (1h)J(FH) spin-spin coupling transmission either for 4-bromo-2-fluorophenol or 2-fluorophenol. In fact, according to a quantum theory of atoms in molecules analysis, no bond critical point is found between O-H and F moieties. The nature of the transmission mechanism of the Fermi contact term of the (1h)J(FH) spin-spin coupling is studied by analyzing canonical molecular orbitals (see J. Phys. Chem. A 2010, 114, 1044), and it is observed that virtual orbitals play only a quite minor role in its transmission. This is typical of a Fermi contact term transmitted mainly through exchange interactions owing to the overlap of proximate electronic clouds; therefore, it is suggested to identify them as (nTS)J(FH) coupling where n stands for the number of formal bonds separating the coupling nuclei. In the cases studied in this work is n = 4. Results presented in this work could provide an interesting rationalization for different experimental signs known in the current literature for proximate J(FH) couplings. 相似文献
49.
The formation of mixed micelles built of 7,12-dioxolithocholic and the following hydrophobic bile acids was examined by conductometric method: cholic (C), deoxycholic (D), chenodeoxycholic (CD), 12-oxolithocholic (12-oxoL), 7-oxolithocholic (7-oxoL), ursodeoxycholic (UD) and hiodeoxycholic (HD). Interaction parameter (β) in the studied binary mixed micelles had negative value, suggesting synergism between micelle building units. Based on β value, the hydrophobic bile acids formed two groups: group I (C, D and CD) and group II (12-oxoL, 7-oxoL, UD and HD). Bile acids from group II had more negative β values than bile acids from group I. Also, bile acids from group II formed intermolecular hydrogen bonds in aggregates with both smaller (2) and higher (4) aggregation numbers, according to the analysis of their stereochemical (conformational) structures and possible structures of mixed micelles built of these bile acids and 7,12-dioxolithocholic acid. Haemolytic potential and partition coefficient of nitrazepam were higher in mixed micelles built of the more hydrophobic bile acids (C, D, CD) and 7,12-dioxolithocholic acid than in micelles built only of 7,12-dioxolithocholic acid. On the other hand, these mixed micelles still had lower values of haemolytic potential than micelles built of C, D or CD. The mixed micelles that included bile acids: 12-oxoL, 7-oxoL, UD or HD did not significantly differ from the micelles of 7,12-dioxolithocholic acid, observing the values of their haemolytic potential. 相似文献
50.