全文获取类型
| 收费全文 | 2767篇 |
| 免费 | 41篇 |
| 国内免费 | 8篇 |
专业分类
| 化学 | 1742篇 |
| 晶体学 | 14篇 |
| 力学 | 49篇 |
| 数学 | 340篇 |
| 物理学 | 531篇 |
| 无线电 | 140篇 |
出版年
| 2023年 | 20篇 |
| 2022年 | 20篇 |
| 2021年 | 34篇 |
| 2020年 | 63篇 |
| 2019年 | 64篇 |
| 2018年 | 30篇 |
| 2017年 | 30篇 |
| 2016年 | 98篇 |
| 2015年 | 82篇 |
| 2014年 | 85篇 |
| 2013年 | 121篇 |
| 2012年 | 182篇 |
| 2011年 | 165篇 |
| 2010年 | 114篇 |
| 2009年 | 97篇 |
| 2008年 | 137篇 |
| 2007年 | 122篇 |
| 2006年 | 133篇 |
| 2005年 | 110篇 |
| 2004年 | 126篇 |
| 2003年 | 97篇 |
| 2002年 | 90篇 |
| 2001年 | 69篇 |
| 2000年 | 51篇 |
| 1999年 | 43篇 |
| 1998年 | 47篇 |
| 1997年 | 36篇 |
| 1996年 | 37篇 |
| 1995年 | 29篇 |
| 1994年 | 39篇 |
| 1993年 | 22篇 |
| 1992年 | 24篇 |
| 1991年 | 27篇 |
| 1990年 | 18篇 |
| 1989年 | 12篇 |
| 1988年 | 14篇 |
| 1987年 | 13篇 |
| 1986年 | 10篇 |
| 1985年 | 18篇 |
| 1984年 | 21篇 |
| 1983年 | 18篇 |
| 1982年 | 20篇 |
| 1981年 | 14篇 |
| 1980年 | 17篇 |
| 1979年 | 19篇 |
| 1978年 | 20篇 |
| 1976年 | 11篇 |
| 1975年 | 17篇 |
| 1974年 | 11篇 |
| 1973年 | 13篇 |
排序方式： 共有2816条查询结果，搜索用时 15 毫秒
991.
Dr. Jan-Philipp Venne Dr. Bastian Feldscher Dr. Stephan Walleck Anja Stammler Dr. Hartmut Bögge Prof. Dr. Jürgen Schnack Prof. Dr. Thorsten Glaser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):4992-5004
The anisotropy barrier of polynuclear single-molecule magnets is expected to be higher with less tunneling the better stabilized the spin ground state is so that less MS mixing in the ground state and with excited spin states occur. We have realized this experimentally in two structurally related heptanuclear SMMs: the triplesalen-based [MnIII 6 CrIII]3+ and the triplesalalen-based *[MnIII 6 CrIII]3+ . The ligand system triplesalen was developed to enforce ferromagnetic interactions by the spin-polarization mechanism. However, we found weak antiferromagnetic couplings, that we assigned to an inefficient spin-polarization by a heteroradialene formation. To prevent this heteroradialene formation, the triplesalalen ligand H6talalen was designed. Here, we present the building block [(talalen )MnIII3]3+ and its application for the assembly of [{(talalen )MnIII3}2{CrIII(CN)6}]3+ (= *[MnIII 6 CrIII]3+ ). Both the trinuclear and heptanuclear complexes are SMMs. The comparison to the related triplesalen complex [(feld )MnIII3]3+ proves the absence of heteroradialene character and the enforcement of ferromagnetic MnIII-MnIII interactions in the (talalen )6− complexes. This results in an increase of the barrier for spin reversal Ueff from 25 K in the triplesalen-based [MnIII 6 CrIII]3+ SMMs to 37 K in the triplesalalen-based *[MnIII 6 CrIII]3+ SMM proving the success of our concept. Based on this study, the next step in the rational improvement of our SMMs is discussed. 相似文献
992.
Tobias Santowski Alexander G. Sturm Dr. Kenrick M. Lewis Dr. Thorsten Felder Prof. Dr. Max C. Holthausen Prof. Dr. Norbert Auner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3809-3815
The Müller–Rochow direct process (DP) for the large-scale production of methylchlorosilanes MenSiCl4−n (n=1–3) generates a disilane residue (MenSi2Cl6−n, n=1–6, DPR) in thousands of tons annually. This report is on methylchlorodisilane cleavage reactions with use of phosphonium chlorides as the cleavage catalysts and reaction partners to preferably obtain bifunctional monosilanes MexSiHyClz (x=2, y=z=1; x,y=1, z=2; x=z=1, y=2). Product formation is controlled by the reaction temperature, the amount of phosphonium chloride employed, the choice of substituents at the phosphorus atom, and optionally by the presence of hydrogen chloride, dissolved in ethers, in the reaction mixture. Replacement of chloro by hydrido substituents at the disilane backbone strongly increases the overall efficiency of disilane cleavage, which allows nearly quantitative silane monomer formation under comparably moderate conditions. This efficient workup of the DPR thus not only increases the economic value of the DP, but also minimizes environmental pollution. 相似文献
993.
994.
995.
996.
Michael Zirbes Dominik Schmitt Nicole Beiser Dominik Pitton Prof. Thorsten Hoffmann Prof. Siegfried R. Waldvogel 《ChemElectroChem》2019,6(1):155-161
Electrochemical oxidative degradation is one of the most promising methods for generation of phenolic fine chemicals from the renewable feedstock lignin. High selectivity, no reagent waste, as well as cost efficiency are major advantages of this particular process. Application of Ni- and Co-based anode materials led to the best results in respect to product yield and selectivity. Interestingly, repeated use of Ni foam electrodes for electrochemical oxidative degradation resulted in significantly increased yields of vanillin, indicating a modification of the electrode surface. In particular, activation of the electrodes by electrochemical treatment of black liquor enabled an activation which further increased the electrocatalytic activity as well as the yield of the aroma chemical vanillin up to more than 100 % compared to non-activated Ni foam electrodes. Additionally, this activated electrode surface was analyzed via flowing atmospheric pressure afterglow surface desorption mass spectrometry (FAPA-MS). The measurement revealed diaminotoluene as a major compound in this adsorption layer, which indicates that this compound is partly responsible for the activation process. Most likely, electrochemical induced deposition of such an organic surface layer enhances the lipophilicity of the electrode surface and increases the accessibility of relevant structural features of lignin particles to the anodic surface, resulting in a higher yield of the desired degradation product vanillin. 相似文献
997.
M. Sc. Finn Burg Dr. Maxime Gicquel Dr. Stefan Breitenlechner Dr. Alexander Pöthig Prof. Dr. Thorsten Bach 《Angewandte Chemie (International ed. in English)》2018,57(11):2953-2957
A chiral manganese porphyrin complex with a two‐point hydrogen‐bonding site was prepared and probed in catalytic C?H oxygenation reactions of 3,4‐dihydroquinolones. The desired oxygenation occurred with perfect site selectivity at the C4 methylene group and with high enantioselectivity in favor of the respective 4S‐configured secondary alcohols (12 examples, 29–97 % conversion, 19–68 % yield, 87–99 % ee). Mechanistic studies support the hypothesis that the reaction proceeds through a rate‐ and selectivity‐determining attack of the reactive manganese oxo complex at the hydrogen‐bound substrate and an oxygen transfer by a rebound mechanism. 相似文献
998.
Thorsten Scherpf Christopher Schwarz Lennart T. Scharf Jana‐Alina Zur Andreas Helbig Prof. Dr. Viktoria H. Gessner 《Angewandte Chemie (International ed. in English)》2018,57(39):12859-12864
Phosphines are important ligands in homogenous catalysis and have been crucial for many advances, such as in cross‐coupling, hydrofunctionalization, or hydrogenation reactions. Herein we report the synthesis and application of a novel class of phosphines bearing ylide substituents. These phosphines are easily accessible via different synthetic routes from commercially available starting materials. Owing to the extra donation from the ylide group to the phosphorus center the ligands are unusually electron‐rich and can thus function as strong electron donors. The donor capacity surpasses that of commonly used phosphines and carbenes and can easily be tuned by changing the substitution pattern at the ylidic carbon atom. The huge potential of ylide‐functionalized phosphines in catalysis is demonstrated by their use in gold catalysis. Excellent performance at low catalyst loadings under mild reaction conditions is thus seen in different types of transformations. 相似文献
999.
Benjamin Hupp Dr. Jörn Nitsch Tanja Schmitt Dr. Rüdiger Bertermann Dr. Katharina Edkins Florian Hirsch Prof. Dr. Ingo Fischer Michael Auth Dr. Andreas Sperlich Priv.‐Doz. Dr. Andreas Steffen 《Angewandte Chemie (International ed. in English)》2018,57(41):13671-13675
The investigation of the mechanisms of mechanochromic luminescence is of fundamental importance for the development of materials for photonic sensors, data storage, and luminescence switches. The structural origin of this phenomenon in phosphorescent molecular systems is rarely known and thus the formulation of structure–property relationships remains challenging. Changes in the M–M interactions have been proposed as the main mechanism with d10 coinage metal compounds. Herein, we describe a new mechanism—a mechanically induced reversible formation of a cation–anion exciplex based on Cu–F interactions—that leads to highly efficient mechanochromic phosphorescence and unusual large emission shifts from UV‐blue to yellow for CuI complexes. The low‐energy luminescence is thermo‐ and vaporesponsive, thus allowing the generation of white light as well as for recovering the original UV‐blue emission. 相似文献
1000.
A one-dimensional continuum model is presented for a dc-glow-discharge in an electronegative gas between parallel plates. It is based on the local balance equations for particle densities and fluxes of electrons, positive and negative ions, the local electron energy balance and the Poisson equation for the self-consistent electric field. These equations are supplemented by suitably chosen boundary conditions and are solved by the finite difference procedure HEMODES (HEnyey Method Ordinary Differential Equation Solver) which, in particular, can successfully handle the singular point occuring if the inertia term in the ion momentum balance equation is taken into account. Since not all data needed within this treatment for the simulation of realistic electronegative gases were available, a fictitious argon-like gas has been considered which nevertheless can demonstrate the characteristic features of such a discharge. In particular, the influence of variations of the attachment and the ion-ion recombination coefficients on the physical variables has been studied. 相似文献