全文获取类型
收费全文 | 1711篇 |
免费 | 45篇 |
国内免费 | 6篇 |
专业分类
化学 | 1385篇 |
晶体学 | 10篇 |
力学 | 12篇 |
数学 | 70篇 |
物理学 | 285篇 |
出版年
2023年 | 12篇 |
2022年 | 9篇 |
2021年 | 9篇 |
2020年 | 25篇 |
2019年 | 20篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 24篇 |
2015年 | 23篇 |
2014年 | 25篇 |
2013年 | 75篇 |
2012年 | 87篇 |
2011年 | 101篇 |
2010年 | 45篇 |
2009年 | 51篇 |
2008年 | 110篇 |
2007年 | 58篇 |
2006年 | 107篇 |
2005年 | 88篇 |
2004年 | 92篇 |
2003年 | 69篇 |
2002年 | 78篇 |
2001年 | 35篇 |
2000年 | 21篇 |
1999年 | 27篇 |
1998年 | 30篇 |
1997年 | 15篇 |
1996年 | 25篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 28篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 25篇 |
1988年 | 18篇 |
1987年 | 17篇 |
1986年 | 27篇 |
1985年 | 45篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 22篇 |
1981年 | 22篇 |
1980年 | 15篇 |
1979年 | 22篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 16篇 |
排序方式: 共有1762条查询结果,搜索用时 9 毫秒
91.
Retro-allylation of homoallyl alcohol by rhodium catalysis occurs to generate allylrhodium species. This allylrhodium reacts with aldehydes to give the corresponding secondary alcohols in situ. Isomerization of these alcohols proceeds in the same pots to furnish the corresponding saturated ketones in good yields. [reaction: see text] 相似文献
92.
Fukui K Takada Y Sumiyoshi T Imai T Takahashi K 《The journal of physical chemistry. B》2006,110(32):16111-16116
The fragmentation of peptides and oligosaccharides in the gas phase was investigated by means of electrospray ionization Fourier transform ion cyclotron resonance (FTICR) mass spectrometry coupled with dissociation by a laser-cleavage infrared multiphoton dissociation (IRMPD) technique. In this technique, an IR free-electron laser is used as a tunable source of IR radiation to cause cleavage of the ionized samples introduced into the FTICR cell. The gas-phase IRMPD spectra of protonated peptides (substance P and angiotensin II) and two sodiated oligosaccharides (sialyl Lewis X and lacto-N-fucopentaose III) were obtained over the IR scan range of 5.7-9.5 microm. In the IRMPD spectra for the peptide, fragment ions are observed as y/b-type fragment ions in the range 5.7-7.5 microm, corresponding to cleavage of the backbone of the parent amino acid sequence, whereas the spectra of the oligosaccharides have major peaks in the range 8.4-9.5 microm, corresponding to photoproducts of the B/Y type. 相似文献
93.
Single-wall carbon nanotubes supported platinum nanoparticles with improved electrocatalytic activity for oxygen reduction reaction 总被引:3,自引:0,他引:3
Kongkanand A Kuwabata S Girishkumar G Kamat P 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2392-2396
Significant enhancement in the electrocatalytic activity of Pt particles toward oxygen reduction reaction (ORR) has been achieved by depositing them on a single wall carbon nanotubes (SWCNT) support. Compared to a commercial Pt/carbon black catalyst, Pt/SWCNT films cast on a rotating disk electrode exhibit a lower onset potential and a higher electron-transfer rate constant for oxygen reduction. Improved stability of the SWCNT support is also confirmed from the minimal change in the oxygen reduction current during repeated cycling over a period of 36 h. These studies open up ways to utilize SWCNT/Pt electrocatalyst as a cathode in the proton-exchange-membrane-based hydrogen and methanol fuel cells. 相似文献
94.
Suri JT Mitsumori S Albertshofer K Tanaka F Barbas CF 《The Journal of organic chemistry》2006,71(10):3822-3828
Dihydroxyacetone variants have been explored as donors in organocatalytic aldol reactions with various aldehyde and ketone acceptors. The protected form of dihydroxyacetone that was chosen for in-depth study was 2,2-dimethyl-1,3-dioxan-5-one, 1. Among the catalysts surveyed here, proline proved to be superior in terms of yield and stereoselectivities in the construction of various carbohydrate scaffolds. In a fashion analogous to aldolase enzymes, the de novo preparation of L-ribulose, L-lyxose, D-ribose, D-tagatose, 1-amino-1-deoxy-D-lyxitol, and other carbohydrates was accomplished via the use of 1 and proline. In reactions using 2,2-dimethyl-1,3-dioxan-5-one 1 as a donor, (S)-proline can be used as a functional mimic of tagatose aldolase, whereas (R)-proline can be regarded as an organocatalytic mimic of fuculose aldolase. 相似文献
95.
Takaaki Taguchi Masaki Yabe Hitomi Odaki Miki Shinozaki Mikko Metsä-Ketelä Takao Arai Susumu Okamoto Koji Ichinose 《Chemistry & biology》2013,20(4):510-520
Highlights? ActVA-ORF5 is a flavin-dependent monooxygenase required for actinorhodin biosynthesis ? ActVA-ORF5 and its three close homologs were functionally dissected ? ActVA-ORF5 and Gra-21 are bifunctional at C-6/C-8, while Med-7 acts only for C-6 ? AlnT exhibits different regiospecificity for oxidation of tricyclic substrates 相似文献
96.
Three-dimensional porous coordination polymer functionalized with amide groups based on tridentate ligand: selective sorption and catalysis 总被引:1,自引:0,他引:1
Hasegawa S Horike S Matsuda R Furukawa S Mochizuki K Kinoshita Y Kitagawa S 《Journal of the American Chemical Society》2007,129(9):2607-2614
To create a functionalized porous compound, amide group is used in porous framework to produce attractive interactions with guest molecules. To avoid hydrogen-bond formation between these amide groups our strategy was to build a three-dimensional (3D) coordination network using a tridentate amide ligand as the three-connector part. From Cd(NO3)2.4H2O and a three-connector ligand with amide groups a 3D porous coordination polymer (PCP) based on octahedral Cd(II) centers, {[Cd(4-btapa)2(NO3)2].6H2O.2DMF}n (1a), was obtained (4-btapa = 1,3,5-benzene tricarboxylic acid tris[N-(4-pyridyl)amide]). The amide groups, which act as guest interaction sites, occur on the surfaces of channels with dimensions of 4.7 x 7.3 A2. X-ray powder diffraction measurements showed that the desolvated compound (1b) selectively includes guests with a concurrent flexible structural (amorphous-to-crystalline) transformation. The highly ordered amide groups in the channels play an important role in the interaction with the guest molecules, which was confirmed by thermogravimetric analysis, adsorption/desorption measurements, and X-ray crystallography. We also performed a Knoevenagel condensation reaction catalyzed by 1a to demonstrate its selective heterogeneous base catalytic properties, which depend on the sizes of the reactants. The solid catalyst 1a maintains its crystalline framework after the reaction and is easily recycled. 相似文献
97.
Tanaka D Horike S Kitagawa S Ohba M Hasegawa M Ozawa Y Toriumi K 《Chemical communications (Cambridge, England)》2007,(30):3142-3144
Confinement of electron donor guests affords an efficient, photo-induced charge transfer (CT) with the anthracene moieties of a porous coordination polymer. 相似文献
98.
TiO2(B) nanowires and TiO2 anatase nanowires were synthesized by the hydrothermal processing in 10 M NaOH aq. at 150 °C followed by the post-heat treatment at 300-800 °C. As-synthesized Na-free titanate nanowires (prepared by the hydrothermal treatment and repeated ion exchanging by HCl (aq.) were transformed into TiO2(B) structure with maintaining 1-D morphology at 300-500 °C, and further transformed into anatase structure at 600-800 °C with keeping 1-D shape. At 900 °C, they transformed into rod-shaped rutile grains. Microstructure of these 1-D TiO2 nanomaterials is reported. 相似文献
99.
New chelating radical ligands pzNNH, pzINH, and pzbisINH (3-pyrazolyl nitronyl nitroxide, 3-pyrazolyl imino nitroxide, and pyrazole-3,5-diyl bis(imino nitroxide), respectively) were prepared. Complexation of these ligands with Ag+ gave [Ag(pzNN)]n, [Ag(pzIN)]6, and [Ag(pzbisIN)]n containing the corresponding anionic forms of the ligands. From the X-ray crystal structure analysis, [Ag(pzIN)]6 was characterized as a dimer of almost planar triangular moieties where the pyrazolate worked as a bridge, and metal-metal bonds brought about dimerization of triangles. [Ag(pzbisIN)]n was characterized as a uniform zigzag chain consisting of pyrazolate bridges and Ag ions with a cis-Npz-Ag-Npz coordination structure. Antiferromagnetic interactions observed could be analyzed based on the structures determined for both compounds. Ferromagnetic coupling was observed in [Ag(pzNN)]n, and a polymeric structure was assumed although the crystal structure could not be determined. Novel supramolecular architectures using pyrazolate-substituted imino nitroxides have been developed, using the unique coordinative versatility of the pyrazolate derivatives 相似文献
100.
Treatment of 1,6-dialkylhexa-1,5-diene-3,4-diones with bis(iodozincio)methane gave zinc alkoxides of cis-5,6-dialkylcyclohepta-3,7-diene-1,3-diol in good yields at room temperature. The reaction proceeded with high stereospecificity. Bis(iodozincio)methane converted the diketone into the cis-divinylcyclopropane-1,2-diol stereoselectively; this diol transformed into the corresponding cycloheptane derivative stereospecifically via Cope rearrangement. 相似文献