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111.
The condensation of 4-acetamido-3-cyanopyrazolo[3,4-d]pyrimidine ( 5 ) with crystalline 2,3,5-tri-O-acetyl-β- D -ribofuranosyl chloride ( 6 ) has furnished a good yield of nucleoside material ( 7 ) which on treatment with sodium methoxide in methanol provided a high yield of nucleoside which was subsequently established as methyl 4-amino-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]-pyrimidine-3-formimidate monohydrate ( 11 ). The formimidate function of 11 was found to be highly reactive and 11 was readily converted into the corresponding carhoxamidine ( 8 ), carboxamidoxime ( 14 ) and carboxamidrazone ( 15 ) when treated with the appropriate nucleophiles. Treatment of the imidate ( 11 ) with sodium hydrogen sulfide gave a high yield of the thiocarboxamide ( 12 ) which was then readily converted into 4-amino-3-cyano-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 16 ). Aqueous base transformed 11 into 4-amino-1-(β- D -ribofuranosyl)-pyrazolo[3,4-d]pyrimidine-3-carboxamide ( 10 ) while more vigorous basic hydrolysis provided the corresponding carboxylic acid ( 9 ) in nearly quantitative yield. Decarboxylation of 9 proceeded smoothly in hot sulfolane to provide the known 4-amino-1-(β- D -ribofuranosyl)pyrazolo[3,4-d]pyrimidine ( 13 ) in 68% yield which unequivocally established the site of ribosylation and anomeric configuration for all nucleosides reported in this investigation. 相似文献
112.
The synthesis of 1-(β-D-ribofuranosyl)indazole (4), 2-(β-D-ribofuranosyl)indazole (5) and 6-, 5-, and 4-nitro-2-(β-D-ribofuranosyl)indazole (8a, 8b, and 8c, respectively), has been accomplished in good yield by the condensation of the appropriate N-trimethylsilylindazole (1, 6a, 6b, and 6c) with 2,3,5-tri-O-acetyl-D -ribofuranosyl bromide (2) followed by subsequent deacetylation of the reaction products. The site of ribosylation and the assignment of anomeric configuration for all nucleosides reported is discussed. This has furnished the first indazole nucleosides with assigned anomeric configurations and the site of ribosylation has been established on the basis of uv comparisons with model methyl compounds. 相似文献
113.
Barry L. Cline Raymond P. Panzica Leroy B. Townsend 《Journal of heterocyclic chemistry》1978,15(5):839-847
The synthesis of 5-amino-3-(β-D-ribofuranosyl)imidazo[4,5-b ]pyridin-7-one (1-deazaguano-sine) has been accomplished by three different methods. The 6-thioguanosine analog 5-amino-3-(β-D-ribofuranosyl)imidazo [4,5-b ]pyridin-7-thione (1-deaza-6-thioguanosine) has been prepared in situ by a reduction of the corresponding disulfide. The synthesis of various nucleoside precursors of the above compounds by several condensation procedures are described. The procedures used to unequivocally determine the site of ribosylation and anomeric configuration are also discussed. 相似文献
114.
Finite element solutions are presented for the flow of Newtonian and non-Newtonian fluids around a sphere falling along the centreline of a cylindrical tube. Both rotating and stationary tube scenarios are considered. Calculations are reported for three different inelastic constitutive models that manifest shear-thinning, extension-thickening and their combination. The influence of inertia and these various forms of viscous response are examined for their influence upon the drag on the settling particle and the structure of the flow. Simulations are performed by employing a semi-implicit time marching Taylor–Galerkin/pressure-correction finite element algorithm, a fractional-staged scheme of second-order-accuracy. © 1998 John Wiley & Sons, Ltd. 相似文献
115.
The determination of arsenic and selenium in standard reference materials using sector field ICP-MS in high resolution mode 总被引:2,自引:0,他引:2
Ashley T. Townsend 《Fresenius' Journal of Analytical Chemistry》1999,364(6):521-526
Sector field ICP-MS was used to analyse As and Se in a range of standard reference materials (NIST 1643d Water, NIST 1573a
Tomato Leaves, NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine Level 2). A spectral
resolution of m/Δm = 7500 enabled 75As and 77Se to be separated from problematic ArCl interferences. Following microwave acid digestion, solid samples were typically diluted
1 + 99 prior to analysis, while the urine sample was diluted 1 + 9. The water sample was analysed undiluted and diluted 1
+ 9. Despite near baseline spectral separation, 75As and 77Se were still found to be influenced by ArCl at high Cl concentrations, the effect being most pronounced for 77Se. When necessary 82Se was also monitored to determine the accuracy of the 77Se results. Detection limits (LOD, based on 3σ of 10 replicates) for 75As, 77Se and 82Se in ultra-pure water, 1% (w/w) HNO3 and 1% (w/w) HCl were ∼ 0.1, ∼ 0.2 and ∼ 0.5 ng g–1, respectively. Although signal intensities when using high resolution were ∼ 1% of that found when using low resolution mode
(m/Δm = 300), measured As concentrations and certified values were found to agree to within ± 11% for all samples analysed.
The concentration of Se in NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine were found
to be in agreement with certified values to within ± 15– 20%, as measured by 77Se. However, closer agreement (± 5%) was found when these samples were analysed using 82Se. The Se concentration in NIST 1643d Water was found to agree to within ± 5% of the certified value (depending on dilution
factor). Due to the low concentration of Se in NIST 1573a Tomato Leaves, quantitation was not possible (below LOQ, 10σ). As
a consequence of the lower ion transmission when using resolution 7500, analytical precisions were found to be elevated over
that normally observed using low resolution mode, typically ± 5–20% (depending on analyte concentration and isotopic abundance).
Received: 28 December 1998 / Accepted: 9 February 1999 相似文献
116.
Mary E. Rampey Carrie E. Halkyard Angela R. Williams April J. Angel Douglas R. Hurst Jessica D. Townsend Anne E. Finefrock Charles F. Beam Shannon L. Studer-Martinez 《Photochemistry and photobiology》1999,70(2):176-183
Abstract. The carbomethoxyhydrazone of 2'-hydroxyacetophenone was trilithiated with excess lithium diisopropylamide and C-acylated with a variety of benzoate esters followed by acid cyclization of the intermediates to 2-(5-aryl-l-car-bomethoxy-lHpyrazol-3-yl)phenols [3-(2-hydroxyphen-yl)-lH-pyrazoles]. The products were characterized by Fourier transform-IR, l H NMR, 13 C NMR, UV-visible absorption and fluorescence. All the derivatives in n -heptane have an absorption maximum at ˜304 nm and an extremely weak (φr = 10 4 ) fluorescence with maxima in the range of 335–460 nm. The broad range of fluorescence maxima and fluorescence quantum yields is attributed to varying contributions of charge transfer that are dependent on both the identity of the substituent and solvent polarity. A phenomenally large Stokes-shifted fluorescence maximum at 620 nm was observed for 2-(l-car-bomethoxy-5-[4-dimethylaminophenyl]-lff-pyrazol-3-y1)phenol in n-heptane and attributed to excited-state intramolecular proton transfer. As a result, competitive excited-state proton/charge transfer properties have been observed in the pyrazoles studied, of which the spectral properties can be fine tuned by substituent as well as solvent effects. 相似文献
117.
本文对TLD-100(LiF:Mg:Ti)样品的三维热释光(TL)谱进行了测量和分析,观测到了经室温辐照的样品具有64℃、116℃、156℃、190℃、218℃的发光峰及若干个高温峰;其发射谱主要由2.67eV、2.82eV、3.19eV及3.34eV等4个发光带组成.本文还对辐照后的样品进行了吸收光谱的测量.结合前人的报告,对30~300℃热释的发光机理进行了讨论 相似文献
118.
A time-stepping finite element method is used to predict the viscoelastic stresses that arise in a tube-tooling wire-coating problem. The polymer melt HDPE is modelled by a multi-mode Phan-Thien/Tanner constitutive equation. Different flow geometries are considered to address optimisation of the process with respect to minimising the stress induced within the coating produced. The influence of the die itself and the various modes are considered. Relaxation times range for a three-mode model from 10−2 to 102 s and for a seven-mode model from 10−3 to 103 s. Typical Weissenberg numbers may range up to 104. Three modes are sufficient to adequately describe the flow, and shorter/narrower draw-down regions are identified as being preferable. Once an adequate land length has been gathered, that has relaxed the flow stresses prior to draw-down, the actual details of die design are found to be inconsequential to the induced stresses in the delivered coatings. 相似文献
119.
The fact that only two pyrrolo[2,3-d][1,2,3]triazines heterocycles had been reported in the literature prompted us to initiate studies designed to provide additional members of this ring system. Initial attempts to prepare additional derivatives of the 7-unsubstituted pyrrolo[2,3-d][1,2,3]triazin-4-ones were limited by their low chemical reactivity. Subsequently, 7-benzyl-5-carboxamidopyrrolo[2,3-d][1,2,3]triazin-4-one (16) was prepared from diethyl 2-nitropyrrole-3,4,-dicarboxylate via an alkylation, ammonolysis, reduction and intramolecular diazocoupling sequence. Conversion of 16 into 7-benzyl-4-(1,2,4-triazol-1-yl)pyrrolo[2,3-d][1,2,3]triazine-5-carbonitrile (17) was accomplished, and nucleophilic displacements of the 4-triazol-1-yl group were studied. Treatment of 17 with NH3/CH3CN gave a mixture of 4-amino-7-benzylpyrrolo[2,3-d][1,2,3]triazine-5-carbonitrile (19) and 2-amino-1-benzylpyrrole-3,4-dicarbonitrile (21). A mechanism to account for the formation of this mixture is described along with studies on the effect that ammonia concentration and a TFA catalyst have on the product ratio. Compound 19 was converted into the 5-carboxamide and 5-thioamide derivatives of 19. 相似文献
120.
Bayesian, non-linear regression models or artificial neural networks are used to make predictions of dose and dose rate time profiles using calculated dose and/or dose rates soon after event onset. Both methods match a new event to similar historical events before making predictions for the new events. The currently developed Bayesian method categorizes a new event based on calculated dose rates up to 5 h (categorization window) after event onset. Categories are determined using ranges of dose rates from previously observed SEP events. These categories provide a range of predicted asymptotic dose for the new event. The model then goes on to make predictions of dose and dose rate time profiles out to 120 h beyond event onset. We know of no physical significance to our 5 h categorization window. In this paper, we focus on the efficacy of a simple method for SEP event asymptotic dose forecasting. Instead of making temporal predictions of dose and dose rate, we investigate making predictions of ranges of asymptotic dose using only dose rates at times prior to 5 h after event onset. A range of doses may provide sufficient information to make operational decisions such as taking emergency shelter or commencing/canceling extra-vehicular operations. Specifically, predicted ranges of doses that are found to be insignificant for the effect of interest would be ignored or put on a watch list while predicted ranges of greater significance would be used in the operational decision making progress. 相似文献