全文获取类型
收费全文 | 1074篇 |
免费 | 49篇 |
国内免费 | 3篇 |
专业分类
化学 | 760篇 |
晶体学 | 6篇 |
力学 | 33篇 |
数学 | 181篇 |
物理学 | 146篇 |
出版年
2023年 | 15篇 |
2022年 | 14篇 |
2021年 | 19篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 32篇 |
2015年 | 22篇 |
2014年 | 37篇 |
2013年 | 49篇 |
2012年 | 93篇 |
2011年 | 117篇 |
2010年 | 76篇 |
2009年 | 52篇 |
2008年 | 85篇 |
2007年 | 55篇 |
2006年 | 70篇 |
2005年 | 50篇 |
2004年 | 52篇 |
2003年 | 50篇 |
2002年 | 41篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 16篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3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 | 6篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有1126条查询结果,搜索用时 46 毫秒
91.
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
92.
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
93.
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
94.
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
95.
96.
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
97.
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
98.
99.
Agnès Rivaton Sylvain Chambon Jean-Luc Gardette Stéphane Guillerez 《Polymer Degradation and Stability》2010,95(3):278-2251
Polymer-based organic solar cells are known to offer a poor stability in real use conditions, and the photodegradation of the active organic layer plays an important role in the reduced lifetime of the devices. This paper focuses on the photodegradation of two conjugated polymers used in organic solar cells, namely poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV) and poly(3-hexyylthiophene) (P3HT), and their blends with [60]PCBM (methano-fullerene[6,6]-phenyl C61-butyric acid methyl ester), a fullerene derivative. MDMO-PPV and P3HT thin films were submitted to photoageing (λ > 300 nm) in the presence and in the absence of oxygen. The mechanisms by which these polymers degrade were elucidated. P3HT, pristine and blended with PCBM, was shown to be much more stable under illumination than MDMO-PPV. The results showed that, if deposited on an inert substrate and well protected from oxygen with a convenient encapsulation, P3HT:PCBM based active layer should be intrinsically stable for several years in use conditions. 相似文献
100.
Control of degradation of polypropylene during its radical functionalisation with furan and thiophene derivatives 总被引:2,自引:0,他引:2
The traditional melt radical functionalisation of isotactic polypropylene (iPP) with maleic anhydride (MAH) and peroxide affords functionalized samples with a severe decrease of the average molecular weight (MW) due to the β-scission reaction. In this work new push-pull unsaturated molecules were investigated, consisting of a heterocyclic ring conjugated with a double bond bearing an electron attracting group. These molecules were specifically designed as MAH substitute able to limit the iPP degradation, while providing functionalisation through grafting. Butyl 3-(2-furanyl) propenoate (BFA) and butyl 3-(2-thienyl) propenoate (BTA) were comparatively tested. The analysis of the reaction products indicated that both molecules are able to graft onto the iPP backbone by prompt reaction with the macro-radicals formed through H-abstraction from iPP chains, thereby significantly limiting the MW decrease, as the functionalized macro-radicals are stabilized by resonance. Nonetheless, some of iPP macro-radicals can give a parallel chain scission before reacting with the new molecules. In the case of BFA, coupling reactions of the formed macro-radicals can lead to the formation of branched high MW architectures, whereas in the case of the thiophene derivative (BTA) only a partial retaining of polymer chain fragmentation was observed due to the reduction of β-scission. 相似文献