全文获取类型
收费全文 | 2058篇 |
免费 | 40篇 |
国内免费 | 12篇 |
专业分类
化学 | 1346篇 |
晶体学 | 9篇 |
力学 | 83篇 |
数学 | 355篇 |
物理学 | 317篇 |
出版年
2022年 | 16篇 |
2021年 | 31篇 |
2020年 | 27篇 |
2019年 | 41篇 |
2018年 | 28篇 |
2017年 | 17篇 |
2016年 | 60篇 |
2015年 | 28篇 |
2014年 | 42篇 |
2013年 | 87篇 |
2012年 | 89篇 |
2011年 | 111篇 |
2010年 | 64篇 |
2009年 | 71篇 |
2008年 | 97篇 |
2007年 | 102篇 |
2006年 | 99篇 |
2005年 | 109篇 |
2004年 | 94篇 |
2003年 | 80篇 |
2002年 | 54篇 |
2001年 | 32篇 |
2000年 | 36篇 |
1999年 | 38篇 |
1998年 | 22篇 |
1997年 | 29篇 |
1996年 | 33篇 |
1995年 | 37篇 |
1994年 | 26篇 |
1993年 | 14篇 |
1992年 | 26篇 |
1991年 | 12篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 16篇 |
1985年 | 25篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1974年 | 8篇 |
1930年 | 7篇 |
1890年 | 10篇 |
1888年 | 8篇 |
排序方式: 共有2110条查询结果,搜索用时 9 毫秒
81.
Sylvio Barbon Jr. Rodrigo Capobianco Guido Lucimar Sasso Vieira Everthon Silva Fonseca Fabrício Lopes Sanchez Paulo Rogério Scalassara Carlos Dias Maciel José Carlos Pereira Shi-Huang Chen 《Journal of Computational and Applied Mathematics》2009
Dynamic Time Warping (DTW), a pattern matching technique traditionally used for restricted vocabulary speech recognition, is based on a temporal alignment of the input signal with the template models. The principal drawback of DTW is its high computational cost as the lengths of the signals increase. This paper shows extended results over our previously published conference paper, which introduces an optimized version of the DTW that is based on the Discrete Wavelet Transform (DWT). 相似文献
82.
83.
Carla Gasbarri Maurizio Ronci Antonio Aceto Roshan Vasani Gianluca Iezzi Tullio Florio Federica Barbieri Guido Angelini Luca Scotti 《Molecules (Basel, Switzerland)》2021,26(17)
The aim of this work was to deeply investigate the structure and properties of electrochemically synthesized silver nanoparticles (AgNPs) through high-resolution techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), Zeta Potential measurements, and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS). Strong brightness, tendency to generate nanoclusters containing an odd number of atoms, and absence of the free silver ions in solution were observed. The research also highlighted that the chemical and physical properties of the AgNPs seemed to be related to their peculiar oxidative state as suggested by X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRPD) analyses. Finally, the MTT assay tested the low cytotoxicity of the investigated AgNPs. 相似文献
84.
Ethanol production was studied in simultaneous saccharification and fermentation (SSF) of steam-pretreated spruce at 42°C,
using a thermotolerant yeast. Three yeast strains of Kluyveromyces marxianus were compared in test fermentations. SSF experiments were performed with the best of these on 5% (w/w) of substrate at a
cellulase loading of 37 filter paper units/g of cellulose, and a β-glucosidase loading of 38 IU/gof cellulose. The detoxification
of the substrate and the lack of pH control in the experiments increased the final ethanol concentration. The final ethanol
yield was 15% lower compared to SSF with Saccharomyces cerevisiae at 37°C, owing to the cessation of ethanol fermentation after the first 10 h. 相似文献
85.
86.
Guido D. Frey Rian D. Dewhurst Shazia Kousar Bruno Donnadieu Guy Bertrand 《Journal of organometallic chemistry》2008,693(8-9):1674-1682
A series of mono- and dicarbene gold(I) complexes of types Au(CAAC)(Cl) [CAAC = cyclic (alkyl)(amino)carbene] (1) and [Au(CAAC)2]+[X]? (X = Cl, AuCl2) (2) have been prepared through reaction of AuCl(SMe2) with free carbenes a–e, and structurally characterized by single X-ray diffraction studies (1a, 1b, 2d, 2e). In addition two new free cyclic (alkyl)(amino)carbenes (c and e) have been synthesized. 相似文献
87.
Clever GH Söltl Y Burks H Spahl W Carell T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(34):8708-8718
Two isomeric salicylic aldehyde nucleobases have been prepared and incorporated into various DNA duplexes. Reaction with ethylenediamine leads to formation of the well-known salen ligand inside the DNA double helix. Addition of transition-metal ions such as Cu(2+), Mn(2+), Ni(2+), Fe(2+), or VO(2+) results in the formation of metal-salen-base-pair complexes, which were studied by using UV and circular dichroism (CD) spectroscopy. HPLC and ESI mass spectrometric measurements reveal an unusually high stability of the DNA-metal system. These metal-salen complexes act as interstrand cross-links and thereby lead to a strong stabilization of the DNA duplexes, as studied by thermal de- and renaturing experiments. Complex formation is strong enough to override sequence information even when the preorganization of the ligand precursors is unfavorable and the DNA duplex is distorted by the metal complexation. Furthermore, melting-point studies show that the salen complex derived from ligand 2 fits better into the DNA duplex, in accordance with results obtained from the crystal structure of the corresponding copper-salen complex 8. 相似文献
88.
Lucia Calucci Emanuela Grigiotti Guido Pampaloni Calogero Pinzino Piero Zanello 《Journal of organometallic chemistry》2006,691(5):829-836
The reaction of Cr(η6-CH3C6H5)2 with 1-benzoyl-6-hydroxy-6-phenyl fulvene, dbcpH, and with pentakis(methoxycarbonyl)cyclopentadiene, pcmcpH, proceeds with evolution of dihydrogen and the formation of the ionic derivatives [Cr(η6-CH3C6H5)2][X] ([X]− = 1,2-dibenzoylcyclopentadienyl, [dbcp]−, pentakis(methoxycarbonyl)cyclopentadienyl, [pcmcp]−), which have been characterized by IR and EPR spectroscopies, X-ray diffraction and electrochemical techniques. The sterically demanding anions do not affect the structural and electronic properties of the cations in solution but strongly influence crystal packing. In fact, a rare cis-eclipsed conformation of the toluene rings is found for [Cr(η6-CH3C6H5)2][dbcp] · THF, whereas two independent complexes are observed in the unit cell of [Cr(η6-CH3C6H5)2][pcmcp], one with toluene rings in a cis-eclipsed conformation and the other in a staggered conformation (projections of methyl groups form an angle of 151°). 相似文献
89.
John M Pintacuda G Park AY Dixon NE Otting G 《Journal of the American Chemical Society》2006,128(39):12910-12916
Rational drug design depends on the knowledge of the three-dimensional (3D) structure of complexes between proteins and lead compounds of low molecular weight. A novel nuclear magnetic resonance (NMR) spectroscopy strategy based on the paramagnetic effects from lanthanide ions allows the rapid determination of the 3D structure of a small ligand molecule bound to its protein target in solution and, simultaneously, its location and orientation with respect to the protein. The method relies on the presence of a lanthanide ion in the protein target and on fast exchange between bound and free ligand. The binding affinity of the ligand and the paramagnetic effects experienced in the bound state are derived from concentration-dependent (1)H and (13)C spectra of the ligand at natural isotopic abundance. Combined with prior knowledge of the crystal or solution structure of the protein and of the magnetic susceptibility tensor of the lanthanide ion, the paramagnetic data define the location and orientation of the bound ligand molecule with respect to the protein from simple 1D NMR spectra. The method was verified with the ternary 30 kDa complex between the lanthanide-labeled N-terminal domain of the epsilon exonuclease subunit from the Escherichia coli DNA polymerase III, the subunit theta, and thymidine. The binding mode of thymidine was found to be very similar to that of thymidine monophosphate present in the crystal structure. 相似文献
90.
Reuther G Tan KT Vogel A Nowak C Arnold K Kuhlmann J Waldmann H Huster D 《Journal of the American Chemical Society》2006,128(42):13840-13846
Many proteins involved in signal transduction are equipped with covalently attached lipid chains providing a hydrophobic anchor targeting these molecules to membranes. Despite the considerable biological significance of this membrane binding mechanism for 5-10% of all cellular proteins, to date very little is known about structural and dynamical features of lipidated membrane binding domains. Here we report the first comprehensive study of the molecular dynamics of the C-terminus of membrane-associated full-length lipidated Ras protein determined by solid-state NMR. Fully functional lipid-modified N-Ras protein was obtained by chemical-biological synthesis ligating the expressed water soluble N-terminus with a chemically synthesized (2)H or (13)C labeled lipidated heptapeptide. Dynamical parameters for the lipid chain modification at Cys 181 were determined from static (2)H NMR order parameter and relaxation measurements. Order parameters describing the amplitude of motion in the protein backbone and the side chain were determined from site-specific measurements of (1)H-(13)C dipolar couplings for all seven amino acids in the membrane anchor of Ras. Finally, the correlation times of motion were determined from temperature dependent relaxation time measurements and analyzed using a modified Lipari Szabo approach. Overall, the C-terminus of Ras shows a versatile dynamics with segmental fluctuations and axially symmetric overall motions on the membrane surface. In particular, the lipid chain modifications are highly flexible in the membrane. 相似文献