全文获取类型
收费全文 | 2258篇 |
免费 | 82篇 |
国内免费 | 28篇 |
专业分类
化学 | 1457篇 |
晶体学 | 27篇 |
力学 | 57篇 |
数学 | 447篇 |
物理学 | 380篇 |
出版年
2023年 | 16篇 |
2022年 | 13篇 |
2021年 | 83篇 |
2020年 | 50篇 |
2019年 | 53篇 |
2018年 | 45篇 |
2017年 | 43篇 |
2016年 | 91篇 |
2015年 | 75篇 |
2014年 | 99篇 |
2013年 | 145篇 |
2012年 | 137篇 |
2011年 | 145篇 |
2010年 | 99篇 |
2009年 | 102篇 |
2008年 | 136篇 |
2007年 | 139篇 |
2006年 | 117篇 |
2005年 | 106篇 |
2004年 | 97篇 |
2003年 | 79篇 |
2002年 | 55篇 |
2001年 | 37篇 |
2000年 | 38篇 |
1999年 | 32篇 |
1998年 | 37篇 |
1997年 | 22篇 |
1996年 | 18篇 |
1995年 | 26篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 23篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1966年 | 1篇 |
排序方式: 共有2368条查询结果,搜索用时 19 毫秒
991.
992.
Prof. Dr. Holger Braunschweig Dr. Mehmet Ali Celik Dr. Rian D. Dewhurst Dr. Katharina Ferkinghoff Dr. Krzysztof Radacki Felix Weißenberger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8596-8602
Heating the metalloborylene complex [{(η5‐C5Me5)Fe(CO)2}(μ‐B){Cr(CO)5}] with alkynes and diynes leads to the formation of B‐metallated borirenes and a bis(B‐metallated borirene) through formal transfer of the metalloborylene moiety [(η5‐C5Me5)(OC)2Fe(B:)]. By using this protocol, a range of B‐metallated borirenes with electron‐donating and electron‐withdrawing substituents are prepared, and these are studied spectroscopically, structurally, and computationally. The yellow‐orange color of the complexes is additionally explained through time‐dependent density functional theory calculations. 相似文献
993.
Kalinski Krzysztof J. Galewski Marek A. Mazur Michal R. Morawska Natalia 《Meccanica》2021,56(4):825-840
Meccanica - The paper presents an original method concerning vibration suppression problem during milling of large-size and geometrically complicated workpieces with the use of novel way of... 相似文献
994.
995.
Jakub Ostapko Dr. Krzysztof Nawara Michał Kijak Dr. Joanna Buczyńska Dr. Barbara Leśniewska Dr. Mariusz Pietrzak Grażyna Orzanowska Prof. Jacek Waluk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(48):17311-17320
Among seven possible nitrogen‐in constitutional isomers of porphyrin only one, porphycene, has been obtained so far in the free, unsubstituted form. Herein, the synthesis of another isomer, parent hemiporphycene ( HPc ), and its thorough structural, spectral, photophysical, electrochemical, and theoretical characterization are reported. Most of the properties of HPc are intermediate between those of porphyrin and porphycene, as evidenced by the values of inner‐cavity dimensions, orbital‐energy splittings, absorption coefficients, magnetic circular dichroism parameters, NH‐stretching frequencies, fluorescence quantum yields, tautomerization rates, and redox potentials. The largest differences arise with respect to tautomerism, due to the low symmetry of HPc and inequivalence of the four nitrogen atoms that define the inner cavity. Two trans tautomers are observed, separated in energy by about 1 kcal mol?1. Tautomerization from the higher‐ to the lower‐energy form is detected in the lowest‐excited singlet state and occurs at a rate that is about four orders of magnitude lower than that observed for porphycene. Hemiporphycene is a very good model for the investigation of inequivalent intramolecular H‐bonds present in one molecule; two such bonds in HPc reveal unusual characteristics, and the bond strength results from the interplay between the N ??? N distance and the N?H?N angle. 相似文献
996.
Kyle F. Augustine Thomas G. Ribelli Marco Fantin Pawel Krys Yidan Cong Krzysztof Matyjaszewski 《Journal of polymer science. Part A, Polymer chemistry》2017,55(18):3048-3057
The external order in reagents for the activation of alkyl halides by Cu0 was investigated in supplemental activator and reducing agents (SARA) ATRP. Using methyl 2-bromopropionate (MBrP) or ethyl α-bromophenylacetate (EBPA) and tris(2-(dimethylamino)ethyl)amine (Me6TREN) in DMSO and MeCN, it was determined that the rate of activation scaled with (S/V)0.9 in both solvents. For MBrP, the rate was first order with respect to [MBrP]0 until a saturation in the rate was observed around 33 and 110 mM in DMSO and MeCN, respectively. For EBPA, the reaction was also first order until a maximum rate was observed at 33 mM in DMSO, whereas an inverse order was observed for concentrations above 66 mM in MeCN. At saturated concentrations of MBrP, it was found that the rate increased linearly with respect to [Me6TREN]0 for all systems but became asymptotic with a maximum rate of 2 × 10−6 and 4 × 10−5 M s−1 in DMSO and MeCN, respectively. Model polymerizations in the absence of ligand showed slow reaction rates, indicating the necessity for ligand. The results allow more accurate modeling and understanding of SARA ATRP under a large range of initiator concentrations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3048–3057 相似文献
997.
Piotr Pospiech Julian Chojnowski Urszula Mizerska Tomasz Makowski Krzysztof Strzelec Natalia Sienkiewicz 《应用有机金属化学》2016,30(6):399-407
Polysiloxane microspheres containing a large number of silanol groups were obtained by an emulsion process of modified polyhydromethylsiloxane. N‐substituted imidazole groups were grafted on these microspheres by the silylation of their silanol groups with N‐[γ‐(dimethylchlorosilyl)propyl]imidazole hydrochloride. The progress of the reaction was monitored using 29Si and 13C magic angle spinning (MAS) NMR and its impact on microsphere morphology was studied using scanning electron microscopy (SEM). The usefulness of the imidazole‐functionalized microspheres as a support for a metal catalyst was demonstrated by their reaction with PdCl2(PhCN)2. In this way a new heterogenized catalyst, Pd(II) complex with imidazole ligands supported on polysiloxane microspheres, was generated. This catalyst, MPd , was characterized using 13C and 29Si MAS NMR, X‐ray photoelectron, Fourier transform infrared and far‐infrared spectroscopies, X‐ray diffraction, SEM–energy‐dispersive X‐ray spectroscopy and wide‐angle X‐ray scattering. The catalyst appears in two structures, as Pd(II) complex and Pd(0) nanoclusters. Its catalytic activity was tested using a model reaction, the hydrogenation of cinnamaldehyde, and compared with that of an analogous complex operating in a homogeneous system. MPd showed a high activity in the promotion of hydrogenation of cinnamaldehyde. The activity in the substrate conversion was stable at least in five cycles of this reaction. The main product was hydrocinnamaldehyde which could be obtained with a yield above 70%. A mechanism of the reaction is proposed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
998.
We study the one-dimensional nonlinear Nernst–Planck–Poisson system of partial differential equations with the class of nonlinear boundary conditions which cover the Chang–Jaffé conditions. The system describes certain physical and biological processes, for example ionic diffusion in porous media, electrochemical and biological membranes, as well as electrons and holes transport in semiconductors. The considered boundary conditions allow the physical system to be not only closed but also open. Theorems on existence, uniqueness, and nonnegativity of local weak solutions are proved. The main tool used in the proof of the existence result is the Schauder–Tychonoff fixed point theorem. 相似文献
999.
1000.