全文获取类型
收费全文 | 1044篇 |
免费 | 46篇 |
国内免费 | 3篇 |
专业分类
化学 | 737篇 |
晶体学 | 6篇 |
力学 | 34篇 |
数学 | 173篇 |
物理学 | 143篇 |
出版年
2023年 | 11篇 |
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 30篇 |
2015年 | 22篇 |
2014年 | 35篇 |
2013年 | 48篇 |
2012年 | 87篇 |
2011年 | 117篇 |
2010年 | 76篇 |
2009年 | 54篇 |
2008年 | 82篇 |
2007年 | 58篇 |
2006年 | 70篇 |
2005年 | 50篇 |
2004年 | 53篇 |
2003年 | 50篇 |
2002年 | 43篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1093条查询结果,搜索用时 343 毫秒
81.
Vincent Besse Gabriel Foyer Rémi Auvergne Sylvain Caillol Bernard Boutevin 《Journal of polymer science. Part A, Polymer chemistry》2013,51(15):3284-3296
This article describes the synthesis of new cyclic compounds able to react with amines to get nonisocyanate polyurethanes (NIPUs). The contribution of the most studied five‐membered cyclic carbonate was compared to five‐membered cyclic dithiocarbonate analogous and to a six‐membered cyclic carbonate. Difunctional reactive species were obtained by a simple substitution reaction or an efficient thiol–ene coupling reaction. The products, obtained with high yields, were characterized by 1H NMR, 13C NMR, and Fourier tansform infrared spectroscopy analysis. The dicyclocarbonates were then used to synthesize NIPUs by step growth polymerization with several diamines. These materials exhibited glass transition temperatures from 19 to ?29 °C, molar mass from 1800 to 20,400 g mol?1, and a 20% mass loss temperature (Td = 20%) between 249 and 296 °C. Such materials are interesting candidates for coating applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3284–3296 相似文献
82.
Raoul Mens Sabine Bertho Sylvain Chambon Jan D'Haen Laurence Lutsen Jean Manca Jan Gelan Dirk Vanderzande Peter Adriaensens 《Journal of polymer science. Part A, Polymer chemistry》2011,49(7):1699-1707
The optimization and control of the nanomorphology of thin films used as active layer in bulk heterojunction (BHJ) plastic solar cells is of key importance for a better understanding of the photovoltaic mechanisms and for increasing the device performances. Hereto, solid‐state NMR relaxation experiments have been evaluated to describe the film morphology of one of the “work‐horse” systems poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylene‐vinylene)/[6, 6]‐phenyl‐C61butyric acid methyl ester (MDMO‐PPV/PCBM) in a quantitative way. Attention is focused on the influence of the processing solvent (toluene vs. chlorobenzene), the blend composition, and the casting technique, that is, spin coating versus doctor blading. It is demonstrated that independently of the solvent and casting technique, part of the PCBM becomes phase separated from the mixed phase. Whereas casting from toluene results in the development of well‐defined PCBM crystallites, casting from chlorobenzene leads to the formation of PCBM‐rich domains that contain substructures of weakly organized PCBM nanoclusters. The amount and physico‐chemical state of the phase separated PCBM is quantified by solid‐state NMR relaxation times experiments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
83.
Eric Lamballais Véronique Fortuné Sylvain Laizet 《Journal of computational physics》2011,230(9):3270-3275
In this short note, we show how to use a highly accurate finite-difference scheme to compute second derivatives in the Navier–Stokes equations while ensuring targeted numerical dissipation. This approach, essentially non conservative, is shown to be close to an upwind method and is straightforward to implement with a negligible computational extra cost. The benefit offered by the resulting discrete operator is illustrated for the direct computation of sound in aeroacoustics and in the more general context of large-eddy simulation through connections with hyperviscosity and spectral vanishing viscosity. 相似文献
84.
Otfried Cheong Xavier Goaoc Andreas Holmsen Sylvain Petitjean 《Discrete and Computational Geometry》2008,39(1-3):194-212
We prove Helly-type theorems for line transversals to disjoint unit balls in ℝ
d
. In particular, we show that a family of n≥2d disjoint unit balls in ℝ
d
has a line transversal if, for some ordering ≺ of the balls, any subfamily of 2d balls admits a line transversal consistent with ≺. We also prove that a family of n≥4d−1 disjoint unit balls in ℝ
d
admits a line transversal if any subfamily of size 4d−1 admits a transversal.
Andreas Holmsen was supported by the Research Council of Norway, prosjektnummer 166618/V30. Otfried Cheong and Xavier Goaoc
acknowledge support from the French-Korean Science and Technology Amicable Relationships program (STAR). 相似文献
85.
An efficient synthesis of 9,10-disubstituted phenanthrenes is described in this Letter. These novel useful building blocks were obtained in a one-pot reaction including Suzuki-Miyaura cross-coupling followed by a Dieckmann-Thorpe ring closure under microwave irradiation. The selection of the appropriate reagents and the optimal reaction conditions to isolate the intermediate biphenyl compound or the final substituted phenanthrenes in high yields will be discussed in this Letter. 相似文献
86.
We report here several synthesis routes and their respective drawbacks/advantages for the preparation of pure LiFePO4. We demonstrate the possibility of using LiFePO4 for electrochemical applications, with respect that an effective carbon coating was realized onto the smallest particles. Actually, to bypass the weak ionic conductivity of lithium iron phosphate, the thinnest would be the particles; the highest would be the performance under severe electrochemical conditions. 相似文献
87.
88.
This work presents the synthesis of novel unsymmetrical bolaamphiphiles bearing a sugar residue and a cationic glycine betaine moiety connected to both ends of a C22 or C32 oligomethylene bridging chain possessing or not a diacetylenic unit. Preliminary transmission electron microscopy (TEM) studies revealed the polymorphism of these bola lipids with regard to their self-assembled morphologies in water depending on the presence or not of the diacetylenic functionality and on alkyl chain length. 相似文献
89.
Karim Bouchmella Sylvain G. Dutremez Dr. Christian Guérin Prof. Dr. Jean‐Christophe Longato Françoise Dahan Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(8):2528-2536
Hydrolyses of HC?CSO3SiMe3 ( 1 ) and CH3C?CSO3SiMe3 ( 2 ) lead to the formation of acetylenic sulfonic acids HC?CSO3H?2.33 H2O ( 3 ) and CH3C?CSO3H?1.88 H2O ( 4 ). These acids were reacted with guanidinium carbonate to yield [+C(NH2)3][HC?CSO3?] ( 5 ) and [+C(NH2)3][CH3C?CSO3?] ( 6 ). Compounds 1 – 6 were characterized by spectroscopic methods, and the X‐ray crystal structures of the guanidinium salts were determined. The X‐ray results of 5 show that the guanidinium cations and organosulfonate anions associate into 1D ribbons through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions, whereas association of these ions in 6 is achieved through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) and ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) interactions. The ribbons in 5 associate into 2D sheets through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{3\hfill \atop 6\hfill}}}$ (12) rings, whereas those in 6 are connected through ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) and ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{4\hfill \atop 6\hfill}}}$ (14) rings. Compound 6 exhibits a single‐layer stacking motif similar to that found in guanidinium alkane‐ and arenesulfonates, that is, the alkynyl groups alternate orientation from one ribbon to the next. The stacking motif in 5 is also single‐layer, but due to interlayer hydrogen bonding between sulfonate anions, the alkynyl groups of each sheet all point to the same side of the sheet. 相似文献
90.