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51.
Efficient Bayesian Inference for Multivariate Probit Models With Sparse Inverse Correlation Matrices
Aline Talhouk Arnaud Doucet Kevin Murphy 《Journal of computational and graphical statistics》2013,22(3):739-757
We propose a Bayesian approach for inference in the multivariate probit model, taking into account the association structure between binary observations. We model the association through the correlation matrix of the latent Gaussian variables. Conditional independence is imposed by setting some off-diagonal elements of the inverse correlation matrix to zero and this sparsity structure is modeled using a decomposable graphical model. We propose an efficient Markov chain Monte Carlo algorithm relying on a parameter expansion scheme to sample from the resulting posterior distribution. This algorithm updates the correlation matrix within a simple Gibbs sampling framework and allows us to infer the correlation structure from the data, generalizing methods used for inference in decomposable Gaussian graphical models to multivariate binary observations. We demonstrate the performance of this model and of the Markov chain Monte Carlo algorithm on simulated and real datasets. This article has online supplementary materials. 相似文献
52.
Simon Rohrbach Andrew J. Smith Jia Hao Pang Darren L. Poole Tell Tuttle Shunsuke Chiba John A. Murphy 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(46):16518-16540
Jüngste Entwicklungen in der experimentellen und theoretischen Chemie haben zur Identifizierung einer schnell wachsenden Klasse von nukleophilen aromatischen Substitutionsreaktionen geführt, die einem konzertierten Mechanismus (cSNAr) folgen, und nicht dem klassischen, zweistufigen SNAr‐Mechanismus. Während klassische SNAr‐Reaktionen auf die substantielle Aktivierung des aromatischen Ringes durch elektronenziehende Substituenten angewiesen sind, ist eine solche Aktivierung für den konzertierten Reaktionsverlauf nicht zwingend nötig. 相似文献
53.
Molecularly Precise Dendrimer–Drug Conjugates with Tunable Drug Release for Cancer Therapy 下载免费PDF全文
Dr. Zhuxian Zhou Dr. Xinpeng Ma Dr. Caitlin J. Murphy Dr. Erlei Jin Dr. Qihang Sun Prof. Youqing Shen Edward A. Van Kirk Prof. William J. Murdoch 《Angewandte Chemie (International ed. in English)》2014,53(41):10949-10955
The structural preciseness of dendrimers makes them perfect drug delivery carriers, particularly in the form of dendrimer–drug conjugates. Current dendrimer–drug conjugates are synthesized by anchoring drug and functional moieties onto the dendrimer peripheral surface. However, functional groups exhibiting the same reactivity make it impossible to precisely control the number and the position of the functional groups and drug molecules anchored to the dendrimer surface. This structural heterogeneity causes variable pharmacokinetics, preventing such conjugates to be translational. Furthermore, the highly hydrophobic drug molecules anchored on the dendrimer periphery can interact with blood components and alter the pharmacokinetic behavior. To address these problems, we herein report molecularly precise dendrimer–drug conjugates with drug moieties buried inside the dendrimers. Surprisingly, the drug release rates of these conjugates were tailorable by the dendrimer generation, surface chemistry, and acidity. 相似文献
54.
An AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measuring oligofructans and fructan polysaccharide (inulins) in mixed materials and food products. The sample is extracted with hot water, and an aliquot is treated with a mixture of sucrase (a specific sucrose-degrading enzyme), alpha-amylase, pullulanase, and maltase to hydrolyze sucrose to glucose and fructose, and starch to glucose. These reducing sugars are then reduced to sugar alcohols by treatment with alkaline borohydride solution. The solution is neutralized, and excess borohydride is removed with dilute acetic acid. The fructan is hydrolyzed to fructose and glucose using a mixture of purified exo- and endo-inulinanases (fructanase mixture). The reducing sugars produced (fructose and glucose) are measured with a spectrophotometer after reaction with para-hydroxybenzoic acid hydrazide. The samples analyzed included pure fructan, chocolate, low-fat spread, milk powder, vitamin tablets, onion powder, Jerusalem artichoke flour, wheat stalks, and a sucrose/cellulose control flour. Repeatability relative standard deviations ranged from 2.3 to 7.3%; reproducibility relative standard deviations ranged from 5.0 to 10.8%. 相似文献
55.
K. E. Murphy E. S. Beary M. S. Rearick R. D. Vocke 《Analytical and bioanalytical chemistry》2000,368(4):362-370
Lead (Pb) and cadmium (Cd) have been determined in six new environmental standard reference materials (SRMs) using isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS). The SRMs are the following: SRM 1944, New York-New Jersey Waterway Sediment, SRMs 2583 and 2584, Trace Elements in Indoor Dust, Nominal 90 mg/kg and 10,000 mg/kg Lead, respectively, SRMs 2586 and 2587, Trace Elements in Soil Containing Lead from Paint, Nominal 500 mg/kg and 3000 mg/kg Lead, respectively, and SRM 2782, Industrial Sludge. The capabilities of ID ICP-MS for the certification of Pb and Cd in these materials are assessed. Sample preparation and ratio measurement uncertainties have been evaluated. Reproducibility and accuracy of the established procedures are demonstrated by determination of gravimetrically prepared primary standard solutions and by comparison with isotope dilution thermal ionization mass spectrometry (ID TIMS). Material heterogeneity was readily demonstrated to be the dominant source of uncertainty in the certified values. 相似文献
56.
Fiona Brady John F. Gallagher Carol Murphy 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):365-368
The title compounds, C12H13NO4, are derived from l ‐threonine and dl ‐threonine, respectively. Hydrogen bonding in the chiral derivative, (2S/3R)‐3‐hydroxy‐2‐(1‐oxoisoindolin‐2‐yl)butanoic acid, consists of O—Hacid?Oalkyl—H?O=Cindole chains [O?O 2.659 (3) and 2.718 (3) Å], Csp3—H?O and three C—H?πarene interactions. In the (2R,3S/2S,3R) racemate, conventional carboxylic acid hydrogen bonding as cyclical (O—H?O=C)2 [graph set R22(8)] is present, with Oalkyl—H?O=Cindole, Csp3—H?O and C—H?πarene interactions. The COOH group geometry differs between the two forms, with C—O, C=O, C—C—O and C—C=O bond lengths and angles of 1.322 (3) and 1.193 (3) Å, and 109.7 (2) and 125.4 (3)°, respectively, in the chiral structure, and 1.2961 (17) and 1.2210 (18) Å, and 113.29 (12) and 122.63 (13)°, respectively, in the racemate structure. The O—C=O angles of 124.9 (3) and 124.05 (14)° are similar. The differences arise from the contrasting COOH hydrogen‐bonding environments in the two structures. 相似文献
57.
Csontos J Kálmán P Tasi G Kálmán M Murphy RF Lovas S 《Journal of computational chemistry》2008,29(9):1466-1471
The pineal gland hormone melatonin regulates several physiological processes including circadian rhythm and also alleviates oxidative stress‐induced degenerative diseases. In spite of its important biological roles, no high level ab initio conformational study has been conducted to reveal its structural features. In this work, the conformational flexibility of melatonin was investigated using correlated ab initio calculations. Conformers, obtained previously at the Hartree‐Fock level (HF/6‐31G*), were fully optimized using second order Møller‐Plesset perturbation theory applying the frozen core approximation (MP2(FC)/6‐31G*). Furthermore, single‐point MP4(SDQ,FC)/6‐31G*//MP2(FC)/6‐31G* computations were performed to investigate the effect of higher order perturbation terms. The HF and MP2 conformational spaces are considerably different: the initial 128 structures converged into 102 different local minima as confirmed by frequency calculations; 28 new minima appeared and 26 previous HF local minima disappeared; no “all‐trans” C3 side chain conformations are seen at the MP2(FC) level. The MP2 global minimum conformation is stabilized by an aromatic‐side chain interaction. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 相似文献
58.
Iodonium ylides, generated in situ with bisacetoxyiodobenzene, are converted to allyl- or benzyl-substituted oxonium or sulfonium ylides via rhodium- or copper-catalyzed carbene transfer. Except for the S-benzyl example, the resulting ylides undergo rearrangement to the corresponding 2-substituted heterocycles. This demonstrates the first use of iodonium ylides as diazoketone surrogates for the generation and rearrangement of onium ylide intermediates. This abbreviated one-step method proceeds in comparable yields relative to the corresponding two-step route employing diazoketone intermediates. 相似文献
59.
Baijun Liu Dae-Sik Kim Jeffrey Murphy Gilles P. Robertson Michael D. Guiver Serguei Mikhailenko Serge Kaliaguine Yi-Ming Sun Ying-Ling Liu Juin-Yih Lai 《Journal of membrane science》2006,280(1-2):54-64
A series of fluorenyl-containing sulfonated poly(aryl ether ether ketone ketone)s (SPFEEKK) were synthesized via aromatic nucleophilic substitution polymerization. The sulfonation content (SC) was controlled by the feed ratios of sulfonated and nonsulfonated monomers. Flexible and strong membranes in the sulfonic acid form were obtained from cast membranes in the sodium salt forms by treatment with acid. The thermal properties, water uptake, swelling ratio, water state, oxidative stability, proton conductivity and methanol permeability were investigated. All the polymers had proton conductivities greater than 1 × 10−2 S/cm at room temperature, and the conductivity values of m-SPFEEKK-80 and p-SPFEEKK-80 were up to 1.86 × 10−1 and 1.78 × 10−1 S/cm at 100 °C. This series of polymers also possessed good dimensional stability in water and low methanol crossover. 相似文献
60.
Wei Zong Wang A. B. Murphy J. D. Yan Ming Zhe Rong J. W. Spencer M. T. C. Fang 《Plasma Chemistry and Plasma Processing》2012,32(1):75-96
This paper is devoted to the calculation of the chemical equilibrium composition and thermodynamic properties of reacting
mixtures of carbon and water at high temperature. Equilibrium particle concentrations and thermodynamic properties including
mass density, molar weight, entropy, enthalpy and specific heat at constant pressure, sonic velocity, and heat capacity ratio
are determined by the method of Gibbs free energy minimization, using species data from standard thermodynamic tables. The
calculations, which assume local thermodynamic equilibrium, are performed in the temperature range from 400 to 30,000 K for
pressures of 0.10, 1.0, 3.0, 5.0 and 10.0 atm. The properties of the reacting mixture are affected by the possible occurrence
of solid carbon formation at low temperature, and therefore attention is paid to the influence of the carbon phase transition
by comparing the results obtained with and without considering solid carbon formation. The results presented here clarify
some basic chemical process and are reliable reference data for use in the simulation of plasmas in reacting carbon and water
mixtures together with the need of transport coefficients computation. 相似文献