全文获取类型
收费全文 | 565篇 |
免费 | 11篇 |
专业分类
化学 | 387篇 |
晶体学 | 30篇 |
力学 | 21篇 |
数学 | 29篇 |
物理学 | 109篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 19篇 |
2017年 | 14篇 |
2016年 | 12篇 |
2015年 | 18篇 |
2014年 | 28篇 |
2013年 | 37篇 |
2012年 | 42篇 |
2011年 | 52篇 |
2010年 | 20篇 |
2009年 | 24篇 |
2008年 | 29篇 |
2007年 | 23篇 |
2006年 | 52篇 |
2005年 | 26篇 |
2004年 | 22篇 |
2003年 | 8篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有576条查询结果,搜索用时 0 毫秒
91.
Fry RA Kwon KD Komarneni S Kubicki JD Mueller KT 《Langmuir : the ACS journal of surfaces and colloids》2006,22(22):9281-9286
Solid-state NMR spectroscopy and ab initio computational chemistry are used to determine the structure of the complex formed upon adsorption of the mononucleotide 2'-deoxyadenosine 5'-monophosphate (dAMP) to the surface of a mesoporous alumina. In this multi-technique approach, rotational-echo double-resonance NMR results reveal that the phosphate group of dAMP interacts predominantly with octahedrally coordinated aluminum species at the surface, and therefore, adsorption is modeled with both mono- and bidentate sorption of the nucleotide phosphate group with octahedral aluminum. 31P chemical shielding tensors are calculated from the structure of the lowest energy conformations, and these results are compared to tensor values extracted from analysis of spinning-sideband patterns in the experimental 31P cross-polarization magic-angle-spinning NMR spectrum. The chemical shift anisotropy and asymmetry parameter indicate that the binding is via a monodentate, inner-sphere complex. 相似文献
92.
Vutukuru S Bethi SR Kane RS 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):10152-10156
This paper describes the use of surface plasmon resonance (SPR) spectroscopy and self-assembled monolayers (SAMs) to understand the characteristics of surfaces that promote the adsorption of proteins at high ionic strengths (high-salt conditions). We synthesized SAMs presenting different multimodal ligands and determined the influence of surface composition, solution composition, and the nature of the protein on the extent of protein adsorption onto the SAMs. Our results confirm that hydrophobic interactions can contribute significantly to protein adsorption under high-salt conditions. In particular, the extent of protein adsorption under high-salt conditions increased with increasing surface hydrophobicity. The extent of protein adsorption was also influenced by the solution composition and decreased with an increase in the chaotropicity of the anion. The combination of SPR and SAMs is well-suited for studying the interaction of proteins with complex surfaces of relevance to chromatography. 相似文献
93.
Sridhar Ravi Simon Watkins Jon Watmuff Kevin Massey Phred Petersen Matthew Marino Anuradha Ravi 《Experiments in fluids》2012,53(3):637-653
Micro Air Vehicles (MAVs) can be difficult to control in the outdoor environment as they fly at relatively low speeds and are of low mass, yet exposed to high levels of freestream turbulence present within the Atmospheric Boundary Layer. In order to examine transient flow phenomena, two turbulence conditions of nominally the same longitudinal integral length scale (Lxx/c?=?1) but with significantly different intensities (Ti?=?7.2?% and 12.3?%) were generated within a wind tunnel; time-varying surface pressure measurements, smoke flow visualization, and wake velocity measurements were made on a thin flat plate airfoil. Rapid changes in oncoming flow pitch angle resulted in the shear layer to separate from the leading edge of the airfoil even at lower geometric angles of attack. At higher geometric angles of attack, massive flow separation occurred at the leading edge followed by enhanced roll up of the shear layer. This lead to the formation of large Leading Edge Vortices (LEVs) that advected at a rate much lower than the mean flow speed while imparting high pressure fluctuations over the airfoil. The rate of LEV formation was dependent on the angle of attack until 10° and it was independent of the turbulence properties tested. The fluctuations in surface pressures and consequently aerodynamic loads were considerably limited on the airfoil bottom surface due to the favorable pressure gradient. 相似文献
94.
N. R. Thimmegowda G. Sarala C. S. Ananda Kumar S. Chandrappa S. B. Benaka Prasad Sridhar M. Anandalwar J. Shashidhara Prasad K. S. Rangappa 《Journal of chemical crystallography》2009,39(7):484-488
Abstract The compound, 7-chloro-5-cyclopropyl-9-methyl-10-(2-piperidin-1-yl-ethyl)-5,10-dihydro-4,5,6,10-tetraaza-dibenzo[a, d] cyclohepten-11-one,
C22H26N5ClO, crystallizes in the triclinic space group Pī with cell parameters a = 8.918(7) ?, b = 9.297(7) ?, c = 14.184(8) ?, V = 1095.98(1) ?3 and Z = 2. The final residual factor R
1 = 0.0451. The structure exhibits intermolecular hydrogen bonds. The 2-piperidin-1-yl-ethyl ring adopts a chair conformation.
The starting material used to synthesize the title compound is the intermediate compound of well known anti-HIV drug Nevirapine
hence the title compound is having biological importance and hence this crystal structure will helps to structural characterization
of the molecule and also for the molecular modeling it will helps for biological study.
Graphical Abstract The title compound 7-chloro-5-cyclopropyl-9-methyl-10-(2-piperidin-1-yl-ethyl)-5,10-dihydro-4,5,6,10-tetraaza-dibenzo[a, d]
cyclohepten-11-one was synthesized by condensation of 7-chloro-5-cyclopropyl-9-methyl-5,10-dihydro-4,5,6,10-tetraaza-dibenzo[a,
d] cyclohepten-11-one with 1-(2-chloro-ethyl)-piperidine hydrochloride in presence of anhydrous powdered potassium carbonate
as base using N,N-dimethyl formamide as solvent and its crystal structure determined. The title compound derived from bioactive molecule and
it is also having biological importance hence this crystal structure will helps for the structural characterization and the
biological study of the novel molecule.
相似文献
95.
S. Naveen C. S. Ananda Kumar S. B. Benaka Prasad K. Vinaya M. A. Sridhar J. Shashidhara Prasad K. S. Rangappa 《Journal of chemical crystallography》2009,39(6):395-398
Abstract The title compound 1-benzhydryl-4-(toluene-4-sulfonyl)-piperazine was synthesized and the structure was investigated by X-ray
crystallography. The title compound, C24H26N2O2S crystallizes in the monoclinic crystal class in the space group P21/c with cell parameters a = 13.5800(10) ?, b = 8.9630(7) ?, c = 18.9040(10) ?, β = 106.851(3)°, Z = 4 and V = 2202.1(3) ?3. The structure has been solved by direct methods and refined to R
1 = 0.0468 for 3174 observed reflections I > 2σ(I). The structure reveals that the piperazine ring is in a chair conformation. The geometry around the S atom is a distorted
tetrahedron.
Graphical Abstract The title compound 1-benzhydryl-4-(toluene-4-sulfonyl)-piperazine was synthesized and the structure was investigated by X-ray
crystallography. The title compound, C24H26N2O2S crystallizes in the monoclinic crystal class in the space group P21/c with cell parameters a = 13.5800(10) ?, b = 8.9630(7) ?, c = 18.9040(10) ?, β = 106.851(3)°, Z = 4 and V = 2202.1(3) ?3. The structure has been solved by direct methods and refined to R
1 = 0.0468 for 3174 observed reflections I > 2σ(I). The structure reveals that the piperazine ring is in a chair conformation. The geometry around the S atom is a distorted
tetrahedron.
相似文献
M. A. SridharEmail: |
96.
Maheswari S Karthikeyan S Murugan P Sridhar P Pitchumani S 《Physical chemistry chemical physics : PCCP》2012,14(27):9683-9695
Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 : 1, were prepared. The oxygen reduction reaction (ORR) was studied on commercial carbon-supported Pd and carbon-supported PdCo nanocatalysts in aqueous 0.1 M KOH solution with and without methanol. The structure, dispersion, electrochemical characterization and surface area of PdCo/C were determined by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Cyclic Voltammetry (CV), respectively. The electrochemical activity for ORR was evaluated from Linear Sweep Voltammograms (LSV) obtained using a rotating ring disk electrode. The catalysts were evaluated for their electrocatalytic activity towards oxygen reduction reaction (ORR) in Alkaline Polymer Electrolyte Membrane Fuel Cells (APEMFCs). PdCo(3 : 1)/C gives higher performance (85 mW cm(-2)) than PdCo(1 : 1)/C, PdCo(2 : 1)/C and Pd/C. The maximum electrocatalytic activity for ORR in the presence of methanol was observed for PdCo(3 : 1)/C. First principles calculations within the framework of density functional theory were performed to understand the origin of its catalytic activity based on the energy of adsorption of an O(2) molecule on the cluster, structural variation and charge transfer mechanism. 相似文献
97.
Phillips CO Govindarajan S Hamblyn SM Conlan RS Gethin DT Claypole TC 《Langmuir : the ACS journal of surfaces and colloids》2012,28(25):9878-9884
Antibodies were patterned onto flexible plastic films using the flexographic printing process. An ink formulation was developed using high molecular weight polyvinyl alcohol in carbonate-bicarbonate buffer. In order to aid both antibody adhesion and the quality of definition in the printed features, a nitrocellulose coating was developed that was capable of being discretely patterned, thus increasing the signal-to-noise ratio of an antibody array. Printing antibody features such as dots, squares, text, and fine lines were reproduced effectively. Furthermore, this process could be easily adapted for printing of other biological materials, including, but not limited to, enzymes, DNA, proteins, aptamers, and cells. 相似文献
98.
S. Meenakshi S. D. Bhat A. K. Sahu S. Alwin P. Sridhar S. Pitchumani 《Journal of Solid State Electrochemistry》2012,16(4):1709-1721
Hybrid dual-network membranes comprising chitosan (CS)–polyvinyl alcohol (PVA) networks crosslinked with sulfosuccinic acid
(SSA) and glutaraldehyde (GA) and modified with stabilized silicotungstic acid (SWA) are reported for their application in
direct methanol fuel cells (DMFCs). Physico-chemical properties of these membranes are evaluated using thermo-gravimetric
analysis and scanning electron microscopy in conjunction with their mechanical properties. Based on water sorption and proton
conductivity measurements for the membranes, the optimum content of 10 wt.% SWA in the membrane is established. The methanol
crossover for these membranes are studied by measuring the mass balance of methanol using density meter and are found to be
lower compared to Nafion-117 membrane. The membrane–electrode assembly with 10 wt.% stabilized SWA–CS–PVA hybrid membrane
with SSA and GA as crosslinking agent delivers a peak power density of 156 mW cm−2 at a load current density of 400 mA cm−2 and 88 mW cm−2 at a load current density of 300 mA cm−2, respectively, in DMFC at 70 °C. 相似文献
99.
Muralidhara ThimmaiahPeng Li Sridhar RegatiBanglin Chen John Cong-Gui Zhao 《Tetrahedron letters》2012,53(36):4870-4872
Multi-component synthesis of 2-amino-3,5-dicarbonitrile-6-thio-pyridines has been developed by using the reaction of aldehydes, malononitrile, and thiophenols in the presence of a Zn(II) or a Cd(II) metal-organic framework (MOF) as the heterogeneous catalyst. This protocol tolerates different functional groups on the substrates and does not require the use of any organic solvent. Moreover, the Zn(II) and Cd(II) MOF catalysts can be recovered and reused for a number of runs without loss of activity. 相似文献
100.
Basi V. Subba Reddy Nagendra Nath Yadav Nikhil Srivastava Jhillu S. Yadav Balasubramanian Sridhar 《Helvetica chimica acta》2012,95(1):76-86
Ionic liquids were found to be a suitable reaction medium for 1,4‐dipolar cycloaddition reactions of an isoquinoline, an activated alkyne, and a 4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehyde at room temperature to afford [1]benzopyrano‐pyrido‐isoquinoline (=9aH,15H‐benzo[a][1]benzopyrano[2,3‐h]quinolizine) derivatives selectively in good yields. The ionic liquid can be recovered and recycled in further runs without loss of activity. 相似文献