全文获取类型
收费全文 | 4138篇 |
免费 | 81篇 |
国内免费 | 13篇 |
专业分类
化学 | 2682篇 |
晶体学 | 10篇 |
力学 | 55篇 |
数学 | 932篇 |
物理学 | 553篇 |
出版年
2020年 | 30篇 |
2019年 | 30篇 |
2016年 | 52篇 |
2015年 | 52篇 |
2014年 | 71篇 |
2013年 | 159篇 |
2012年 | 92篇 |
2011年 | 136篇 |
2010年 | 83篇 |
2009年 | 102篇 |
2008年 | 131篇 |
2007年 | 117篇 |
2006年 | 122篇 |
2005年 | 124篇 |
2004年 | 109篇 |
2003年 | 99篇 |
2002年 | 102篇 |
2001年 | 44篇 |
2000年 | 45篇 |
1997年 | 59篇 |
1996年 | 55篇 |
1995年 | 60篇 |
1994年 | 72篇 |
1993年 | 65篇 |
1992年 | 67篇 |
1991年 | 48篇 |
1990年 | 59篇 |
1989年 | 79篇 |
1988年 | 88篇 |
1987年 | 77篇 |
1986年 | 43篇 |
1985年 | 69篇 |
1984年 | 58篇 |
1983年 | 37篇 |
1982年 | 57篇 |
1981年 | 59篇 |
1980年 | 73篇 |
1979年 | 66篇 |
1978年 | 67篇 |
1977年 | 46篇 |
1976年 | 44篇 |
1975年 | 59篇 |
1974年 | 56篇 |
1973年 | 65篇 |
1972年 | 43篇 |
1971年 | 46篇 |
1970年 | 50篇 |
1969年 | 35篇 |
1967年 | 34篇 |
1966年 | 44篇 |
排序方式: 共有4232条查询结果,搜索用时 15 毫秒
1.
Dr. Christoph Ludwig Teske Dr. Anna-Lena Hansen Prof. Dr. Richard Weihrich Prof. Dr. Lorenz Kienle Marius Kamp Kasper Pieter van der Zwan Prof. Dr. Jürgen Senker Dr. Carsten Dosche Prof. Dr. Gunther Wittstock Prof. Dr. Wolfgang Bensch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6763-6772
A new preparation route is developed for the synthesis of needle-like crystals of [Au(S2CNH2)2]SCN, which avoids disproportionation of the AuI salt used as a starting material. In the crystal structure, the two crystallographically independent AuIII centers are in a square-planar environment of two S2CNH2 ligands. The Hirshfeld surface analysis reveals the presence of noncovalent intermolecular S⋅⋅⋅S interactions, which are essential for the spatial arrangement of the molecules. Density functional theory (DFT) calculations including dispersion and damping corrections result in a unit cell volume very close to the value determined experimentally. Thermal decomposition in an inert atmosphere generates black needles with lengths of up to 500 μm. X-ray powder diffraction and pair distribution function analyses demonstrate that the needles are composed of nanosized crystals with a volume-weighted average domain size of 20(1) nm. According to results of X-ray photoemission experiments, the black needles are covered by a nitrogen-rich carbon nitride with composition near (CN)2N. 13C solid-state NMR investigations indicate that two different carbon species are present, with signals corresponding well to heptazine units as in melon and triazine units as in poly(triazin imide) type compounds. Scanning transmission electron microscopy tomography evidences that the needles are composed of slightly elongated nanoparticles. 相似文献
2.
3.
4.
Fabio Cameli Prof. Dr. Joop H. ter Horst Dr. René R. E. Steendam Dr. Ir. Christos Xiouras Prof. Dr. Georgios D. Stefanidis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1344-1354
Herein, the pivotal role of secondary nucleation in a crystallization-enhanced deracemization process is reported. During this process, complete and rapid deracemization of chiral conglomerate crystals of an isoindolinone is attained through fast microwave-assisted temperature cycling. A parametric study of the main factors that affect the occurrence of secondary nucleation in this process, namely agitation rate, suspension density, and solute supersaturation, confirms that an enhanced stereoselective secondary nucleation rate maximizes the deracemization rate. Analysis of the system during a single temperature cycle showed that, although stereoselective particle production during the crystallization stage leads to enantiomeric enrichment, undesired kinetic dissolution of smaller particles of the preferred enantiomer occurs during the dissolution step. Therefore, secondary nucleation is crucial for the enhancement of deracemization through temperature cycles and as such should be considered in further design and optimization of this process, as well as in other temperature cycling processes commonly applied in particle engineering. 相似文献
5.
Jarno Riefer Ludwig Zapf Dr. Raphael Wirthensohn Dr. Philipp T. Hennig Dr. Tatjana Ribbeck Dr. Jan A. P. Sprenger Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze 《European journal of organic chemistry》2023,26(17):e202300031
Cyanoborane adducts of the Lewis acids B(CN)3, BF(CN)2, and BH(CN)2 with pyridine and 4-cyanopyridine have been obtained in high yields. The syntheses were accomplished by oxidation of the readily available potassium salts of the cyano(hydrido)borate anions [BH(CN)3]− ( MHB ), [BFH(CN)2]− ( FHB ), and [BH2(CN)2]− ( DHB ) with bromine in the presence of the respective pyridine derivative C5H5N or 4-CN-C5H4N as starting material. All six cyanoborane adducts have been characterized by NMR and vibrational spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The reduction of the cyanoborane adducts has been investigated by cyclic voltammetry and the Lewis acidity of the different cyanoboranes has been assessed using the Gutmann-Beckett method. Selected experimental data and trends are compared to theoretical ones, for example fluoride ion affinities (FIAs). 相似文献
6.
m‐Xylylene bismaleimide, Compimide ? ? Compimide® is a registered trademark.
MXBI (hereafter MXBI), was developed as a building block for formulating bismaleimide resins with improved processability. MXBI on its own, or in combination with 4,4′‐bismaleimidodiphenylmethane (Compimide MDAB, hereafter MDAB) and with 2,2′‐diallylbisphenol‐A as a co‐monomer, provides very low‐melting resin blends, which can be processed at temperatures around 60–80°C via RTM (Resin Transfer Moulding), VARIM (Vacuum Assisted Resin Infusion Moulding), prepregging, and wet filament winding (FW). Uncured and cured resin properties were evaluated. The mechanical property spectrum of the MXBI/MDAB/diallylbisphenol‐A system with varying MXBI/MDAB ratio shows almost equivalent contributions of MXBI and MDAB to the mechanical properties of a system. Higher MXBI proportions are responsible for lower resin viscosities and hence superior processability. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
MXBI (hereafter MXBI), was developed as a building block for formulating bismaleimide resins with improved processability. MXBI on its own, or in combination with 4,4′‐bismaleimidodiphenylmethane (Compimide MDAB, hereafter MDAB) and with 2,2′‐diallylbisphenol‐A as a co‐monomer, provides very low‐melting resin blends, which can be processed at temperatures around 60–80°C via RTM (Resin Transfer Moulding), VARIM (Vacuum Assisted Resin Infusion Moulding), prepregging, and wet filament winding (FW). Uncured and cured resin properties were evaluated. The mechanical property spectrum of the MXBI/MDAB/diallylbisphenol‐A system with varying MXBI/MDAB ratio shows almost equivalent contributions of MXBI and MDAB to the mechanical properties of a system. Higher MXBI proportions are responsible for lower resin viscosities and hence superior processability. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
7.
8.
Susana Chatzipapadopoulos Tobias Zentel Prof. Dr. Ralf Ludwig Matthias Lütgens Prof. Dr. Stefan Lochbrunner Prof. Dr. Oliver Kühn 《Chemphyschem》2015,16(12):2519-2523
Understanding both structure and dynamics is crucial for producing tailor‐made ionic liquids (ILs). We studied the vibrational and structural dynamics of medium versus weakly hydrogen‐bonded C?H groups of the imidazolium ring in ILs of the type [1‐alkyl‐3‐methylimidazolium][bis(trifluoromethanesulfonyl)imide] ([Cnmim][NTf2]), with n=1, 2, and 8, by time‐resolved coherent anti‐Stokes Raman scattering (CARS) and quantum‐classical hybrid (QCH) simulations. From the time series of the CARS spectra, dephasing times were extracted by modeling the full nonlinear response. From the QCH calculations, pure dephasing times were obtained by analyzing the distribution of transition frequencies. Experiments and calculations reveal larger dephasing rates for the vibrational stretching modes of C(2)?H compared with the more weakly hydrogen‐bonded C(4,5)?H. This finding can be understood in terms of different H‐bonding motifs and the fast interconversion between them. Differences in population relaxation rates are attributed to Fermi resonance interactions. 相似文献
9.
10.