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1.
Wang D Schwinden MD Radesca L Patel B Kronenthal D Huang MH Nugent WA 《The Journal of organic chemistry》2004,69(5):1629-1633
The reaction of a variety of methyl esters with dimethylsulfoxonium methylide at 0-25 degrees C affords the chain-extended beta-keto dimethylsulfoxonium ylides. Subsequent treatment with hydrogen chloride in THF proceeds with loss of DMSO to afford the corresponding alpha-chloroketones. This sequence has been utilized to convert the methyl esters of CBZ-protected alanine and valine to the anti N-protected alpha-amino epoxides, which are important pharmaceutical intermediates. When the same protocol is applied to BOC-protected phenylalanine methyl ester, epimerization occurs so that the use of a more reactive aryl ester is required. This chemistry provides a practical route to alpha-chloroketones that avoids the use of toxic and explosive diazomethane. 相似文献
2.
Soluble complex-formation of mercury(II) thiocyanate has been studied oscillometrically. The titration of mercury(II) nitrate with thiocyanate gives one inflection corresponding to the formation of Hg(SCN)2, while in the reverse titration the formation of Hg(SCN)+ is also indecated. The method is useful for a rapid determination of very small quantities of mercury or thiocyanate in highly dilute solutions. The titrations can be effected in presence of nitric acid provided its total acidity in the system does not exceed about N. Further Work on the mercury(II) -halide and mercury(II)-cyanide reactions is in progress. 相似文献
3.
The concerned diols (general abbreviation, H(2)L) are catechol (H(2)L(1)) and its 3,5-Bu(t)(2) derivative (H(2)L(2)). Esters of the type VO(xsal)(HL), 2, are obtained by reacting H(2)L with VO(xsal)(H(2)O) or VO(xsal)(OMe)(HOMe), where xsal(2-) is the diionized salicylaldimine of glycine (x = g), L-alanine (x = a), or L-valine (x = v). The reaction of VO(acac)(2) with H(2)L and the salicylaldimine (Hpsal) of 2-picolylamine has furnished VO(psal)(L), 3. In the structures of VO(gsal)(HL(1)), 2a, and VO(vsal)(HL(2)), 2f, the HL(-) ligand is O,O-chelated, the phenolic oxygen lying trans to the oxo oxygen atom. The xsal(2-) coligand has a folded structure and the conformation of 2f is exclusively endo. In both 2a and 2f the phenolic oxygen atom is strongly hydrogen bonded (O...O, 2.60 A) to a carboxylic oxygen atom of a neighboring molecule. In VO(psal)(L(2)).H(2)O, 3b, the diionized diol is O,O-chelated to the metal and the water molecule is hydrogen bonded to a phenoxidic oxygen atom (O.O, 2.84 A). The C-O and C-C distances in the V(diol) fragment reveal that 2 is a pure catecholate and 3 is a catecholate-semiquinonate hybrid. In solution each ester gives rise to a single (51)V NMR signal (no diastereoisomers), which generally shifts downfield with a decrease in the ester LMCT band energy. The V(V)/V(IV) and catecholate-semiquinonate reduction potentials lie near -0.75 and 0.35, and 1.10 and 0.70 V vs SCE for 2 and 3, respectively. Molecular oxygen reacts smoothly with 2 quantitatively furnishing the corresponding o-quinone, and in the presence of H(2)L the reaction becomes catalytic. In contrast, type 3 esters are inert to oxygen. The initial binding of O(2) to 2 is proposed to occur via hydrogen bonding with chelated HL(-). 相似文献
4.
Ashok K. Singh Amar Singh Ranjana Gupta Madhu Saxena Bharat Singh 《Transition Metal Chemistry》1992,17(5):413-416
The kinetics of oxidation of three aldoses (glucose, mannose and galactose) byN-bromoacetamide (NBA) in the presence of an alkaline solution of RuO4 as catalyst and Hg(OAc)2 as co-catalyst and as a scavenger for bromide have been investigated. The main products of the oxidation are the corresponding
aldonic acids. The reaction is zero order with respect to aldose and OH−. First order dependence of the reaction on both NBA and RuO4 at low concentrations shifts to zero order at higher concentrations. Addition of acetamide decreases the reaction rate, while
addition of Hg(OAc)2 has the opposite effect. No significant effect of ionic strength was observed. OBr− is postulated as the reactive oxidising species and a mechanism involving co-catalysis by RuO4 and HgII is proposed.
TMC 2588 相似文献
5.
Ashok K. Singh Alka Srivastava Ashutosh Kumar Bharat Singh 《Transition Metal Chemistry》1993,18(4):427-430
Summary The kinetics of iridium(III)-catalysed oxidation of 1,2-ethanediol and 1,4-butanediol by N-bromoacetamide (NBA) in HClO4 in the presence of [Hg(OAc)2] as a scavenger for Br– have been investigated. The reactions are zero-order with respect to both diols, and first-order in NBA at low NBA concentrations, tending to zero order at high concentrations. The order in IrIII decreases from unity to zero at high iridium(III) concentrations. A positive effect on the oxidation rate is observed for [H+] and [HgII] whereas a negative effect is observed for acetamide and [Cl–]. Ionic strength does not influence the oxidation rate. (H2OBr)+ is postulated as the oxidizing species. A mechanism consistent with the observed kinetic data is proposed. 相似文献
6.
Ashish Surya?Prakash?Singh Ashok?Kumar?Singh Bharat?SinghEmail author 《Transition Metal Chemistry》2005,30(5):610-615
Kinetics and mechanism of the Os(VIII) catalysed oxidation of crotonic acid (CA) by KBrO3 in alkaline medium have been investigated. Zero order dependence in [KBrO3] was observed, while first order with respect to CA in its lower concentration range tends to zero order at its higher concentration range. The order in [Os(VIII)] was found to be unity and a positive effect of [OH−] was observed. Variation of the ionic strength (μ) and dielectric constant of the medium and addition of Hg(OAc)2 (used as Br− scavenger) had an insignificant effect on the rate of reaction. Thermodynamic parameters have also been calculated and reported. A suitable mechanism consistent with the observed kinetic results has been suggested and the related rate law deduced. 相似文献
7.
The kinetics of thermal reactions of the photochemically-generated species [W(CN)7OH]4− and [W(CN)6–(CNH)(H2O)]2− with 5–nitro-1,10–phenanthroline
(nitrophen) in basic and acidic media, respectively, were studied in buffer solutions at pH 4.2–10.6 and ionic strength 7.5×10−2kg−1
at 20°C. The quantum yield for the formation of the photoproduct was calculated and found to depend upon pH and the ligand
and [W(CN)8]4− concentrations. The rate constants and quantum yields were less compared with 1,10–phenanthroline due to the
electron-withdrawing inductive effect of the nitro group in nitrophen, which makes the latter a weaker ligand. The pseudo-first-order
rate constant and quantum yield values in acidic media are higher than in basic media and the mechanisms of the photochemical
substitution are different in the two media.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Doiphode Vidya Vairale Priti Sharma Vidhika Waghmare Ashish Punde Ashvini Shinde Pratibha Shah Shruti Pandharkar Subhash Hase Yogesh Aher Rahul Nair Shruthi Jadkar Vijaya Bade Bharat Prasad Mohit Rondiya Sachin Jadkar Sandesh 《Journal of Solid State Electrochemistry》2021,25(6):1835-1846
Journal of Solid State Electrochemistry - Herein, we report the synthesis of ZnO nanorod films onto FTO (fluorine-doped tin oxide) substrates using the solution-processed electrodeposition method.... 相似文献
9.
Bharat Kumar Ruth L. Viboh Margel C. Bonifacio William B. Thompson Jonathan C. Buttrick Babe C. Westlake Min‐Soo Kim Robert W. Zoellner Sergey A. Varganov Philipp Mrschel Jaroslav Teteruk Martin U. Schmidt Benjamin T. King 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(51):13071-13071
10.
Venkata Bharat Nishtala 《合成通讯》2013,43(18):2342-2349
Various spirooxindolopyrans and xanthenes were synthesized efficiently through a pseudo-three-component reaction by using deep eutectic solvent (DES) ZnCl2+Urea. The remarkable advantages of this reaction are the usage of an environmentally benign solvent (DES), simple purification method, operational simplicity, less reaction time, and higher yields making the reaction a green protocol. 相似文献