全文获取类型
收费全文 | 653篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 505篇 |
晶体学 | 6篇 |
力学 | 20篇 |
数学 | 16篇 |
物理学 | 128篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 47篇 |
2012年 | 21篇 |
2011年 | 23篇 |
2010年 | 15篇 |
2009年 | 11篇 |
2008年 | 43篇 |
2007年 | 42篇 |
2006年 | 18篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 37篇 |
2002年 | 35篇 |
2001年 | 33篇 |
2000年 | 27篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1932年 | 5篇 |
1906年 | 2篇 |
1903年 | 2篇 |
1898年 | 2篇 |
1886年 | 2篇 |
排序方式: 共有675条查询结果,搜索用时 15 毫秒
91.
92.
Low band‐gap diketopyrrolopyrrole‐containing polymers for near infrared electrochromic and photovoltaic applications 下载免费PDF全文
Jonathan Zhaozhi Low Wei Teng Neo Qun Ye Wen Jie Ong Ivy Hoi Ka Wong Ting Ting Lin Jianwei Xu 《Journal of polymer science. Part A, Polymer chemistry》2015,53(10):1287-1295
Donor–acceptor type polymers bearing diketopyrrolopyrrole and 3,4‐ethylenedioxythiophene units are reported. The polymers are green and exhibit very low band‐gaps (1.19 eV) with strong and broad absorption (maxima of about 830 nm) in the near infrared (NIR) region in their neutral film states. The polymers display color changes between dark green and light blue with exceptional optical contrasts in the NIR regions of up to 78 and 63% as thin films and single‐layer electrochromic devices, respectively. Fast switching, good stabilities as well as high coloration efficiencies (743–901 cm2 C?1) were also observed. The polymers could also be potentially used as photovoltaic material, with a power conversion efficiency of up to 1.68%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1287–1295 相似文献
93.
94.
95.
A. K. Das M. Datta S. K. Mazumdar N. Das A. Van Aerschot J. N. Low R. Alan Howie 《Journal of chemical crystallography》1992,22(4):439-442
The title compound (C9H12N2O5,M
r
=228.2) crystallizes in the trigonal space groupP31,21 witha=b=9.438(3) andc=19.775(3) Å,V=1525.5 Å3,D
x
=1.490 gm cm–3,Z=6,=0.12 mm–1,F(000)=720.0,T=293 K. The structure was solved by direct methods and refined by full-matrix least-squares calculations to anR value of 0.044 on 843 unique observed reflections. The dioxane ring adopts a chair conformation. The crystal structure is stabilized by N-HO hydrogen bonds and C-HO close contacts. 相似文献
96.
Crystals of the hemihydrate of this bile acid are hexagonal, space groupP6522, a=b=13.736(8)Å,c=85.06(6)Å,V=13,899Å3. The asymmetric unit contains two independent steroid molecules and one water molecule, the latter disordered over two nonequivalent positions.Z=12[2(C24H40O5)·1(H2O)],F(000)=5496. Structure solution by direct methods; refinement by least-squares, toR=0.072. The complex hydrogen-bond system comprises: (a) three standard ordered O-HO hydrogen-bonds; (b) what is probably a symmetrically hydrogen-bonded carboxylic acid dimer, with a twofold rotation axisin the plane of the two carboxyl groups; (c) helical hydrogen-bonding chains about each 65 axis, disordered over four possible arrangements. In these helical chains, the six independent hydrogen-bonds can as a group be in either of two systems of nearly equivalent flip-flop arrangements: O-HO OH-O. Each helical system includes water, which can occupy either of two sites; thus, there is further disorder involving two sets of nonequivalent hydrogen-bonds with water as donor and acceptor. Many aggregation features here differ markedly from those in the crystal structures of either anhydrous cholic acid or cholic acid monohydrate. 相似文献
97.
Silvia Cruz Jorge Trilleras Justo Cobo John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(12):o637-o642
3‐tert‐Butyl‐7‐(4‐chlorobenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione ethanol hemisolvate, C30H34ClN3O2·0.5C2H6O, (I), its 7‐(4‐bromobenzyl)‐ analogue, C30H34BrN3O2·0.5C2H6O, (II), and its 7‐(4‐methylbenzyl)‐ analogue, C31H37N3O2·0.5C2H6O, (III), are isomorphous, with the ethanol component disordered across a twofold rotation axis in the space group C2/c. In the corresponding 7‐[4‐(trifluoromethyl)benzyl]‐ compound, C31H34F3N3O2·0.5C2H6O, (IV), the ethanol component is disordered across a centre of inversion in the space group P. In each of (I)–(IV), the reduced pyridine ring adopts a half‐chair conformation. The heterocyclic components in (I)–(III) are linked into centrosymmetric dimers by a single C—H...π interaction, with the half‐occupancy ethanol component linked to the dimer by a combination of C—H...O and O—H...π(arene) hydrogen bonds. The heterocyclic molecules in (IV) are linked into chains of centrosymmetric rings by C—H...O and C—H...π hydrogen bonds, again with the half‐occupancy ethanol component pendent from the chain. The significance of this study lies in the isomorphism of the related derivatives (I)–(III), in the stoichiometric hemisolvation by ethanol, where the disordered solvent molecule is linked to the heterocyclic component by a two‐point linkage, and in the differences between the crystal structures of (I)–(III) and that of (IV). 相似文献
98.
Henry Insuasty Paola Mier Gina Suarez John N. Low Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(1):o27-o30
The molecular dimensions of 2‐ethylsulfanyl‐7‐(4‐methylphenyl)‐4‐phenylpyrazolo[1,5‐a][1,3,5]triazine, C20H18N4S, (I), 7‐(4‐chlorophenyl)‐2‐ethylsulfanyl‐4‐phenylpyrazolo[1,5‐a][1,3,5]triazine, C19H15ClN4S, (II), and 4,7‐bis(4‐chlorophenyl)‐2‐(ethylsulfanyl)pyrazolo[1,5‐a][1,3,5]triazine, C19H14Cl2N4S, (III), show evidence for some aromatic delocalization in the pyrazole rings. The conformations adopted by the ethylsulfanyl substituents are different in all three compounds. There are no hydrogen bonds in any of the crystal structures, but pairs of molecules in (II) and (III) are linked into centrosymmetric dimers by π‐stacking interactions. 相似文献
99.
Fabin Orozco John N. Low Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(7):o379-o381
In the title compound, C34H31N2O8PS, the intramolecular distances provide evidence for polarization of the molecular–electronic structure. The molecules are linked into complex chains of rings by three independent C—H...O hydrogen bonds. The significance of this study lies in its finding that two of the four carbonyl O atoms play no role in the hydrogen bonding, despite the large excess of potential hydrogen‐bond donors present. 相似文献
100.
Sandra L. Gmez Walter Raysth Alirio Palma Justo Cobo John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(9):o519-o523
In (2SR,4RS)‐7‐chloro‐2‐exo‐(4‐chlorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C16H13Cl2NO, (I), the molecules are linked by a combination of C—H...O and C—H...N hydrogen bonds into a chain of edge‐fused R33(12) rings. The isomeric compound (2S,4R)‐7‐chloro‐2‐exo‐(2‐chlorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, (II), crystallizes as a single 2S,4R enantiomer and the molecules are linked into a three‐dimensional framework structure by two C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond. The molecules of (2S,4R)‐7‐chloro‐2‐exo‐(1‐naphthyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C20H16ClNO, (III), are also linked into a three‐dimensional framework structure, here by one C—H...O hydrogen bond and two C—H...π(arene) hydrogen bonds. The significance of this study lies in its observation of the variations in molecular configuration and conformation, and in the variation in the patterns of supramolecular aggregation, consequent upon modest changes in the peripheral substituents. 相似文献