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261.
Sobhani S Fielenbach D Marigo M Wabnitz TC Jørgensen KA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(19):5689-5694
The application of cinchona alkaloid derivatives as catalysts for enantioselective alpha-sulfenylation of activated C-H bonds in lactones, lactams, and beta-dicarbonyl compounds by different electrophilic sulfur reagents is presented. Optically active products are obtained in good to excellent yields and up to 91 % ee. Furthermore, the diastereoselective reduction of alpha-sulfenylated beta-keto esters to give optically active alpha-sulfenylated beta-hydroxy esters has been studied. A model for the intermediate is presented, in which the protonated cinchona alkaloid interacts with the substrate leading to face-shielding in accordance with the enantioselective alpha-sulfenylation step. 相似文献
262.
Aluminium trichloride forms the adducts AlCl3 · NH2CH3, AlCl3 · 2NH2CH3, AlCl3 · 4NH2CH3; AlCl3 · NH3CH3Cl, AlCl3 · 2NH3CH3Cl. The interaction between AlCl3, PCl5 and NH3CH3Cl in the molar ratio 1:3:2 proceeds according to the reaction equation in “Inhaltsübersicht”. On applying other stoichiometric amounts, [Cl2(NHCH3)P? N(CH3)? AlCl3] · HCl and [Cl3P? N(CH3)? AlCl3] · HCl are obtained; the latter reacts as [Cl3P? NHCH3][AlCl4]. At the molar ratio AlCl3:PCl5:NH3CH3Cl = 1:2:4 a compound is formed being presumably the six-membered heterocycle formulated in “Inhaltsübersicht”. With [Cl3P?N? PCl3] and aluminium chloride [Cl3P?N? PCl3][AlCl4] is formed. 相似文献
263.
Synthesis and Properties of the 1,3-Benzazaphospholes 1H-1,3-Benzazaphospholes (R = H, CH3, C6H5, N(CH3)2) are synthesized not only rom o-aminophenylphosphines and different cyclisation compounds such as R? C(OR)?NH · HCl, R? C(O)Cl, R? COOR′, R? C(OCH3)2NR′2, or Cl2C?N(CH3)2Cl but also from secondary o-aminophenylphosphines PRH? C6H4? NH2 (R = C6H5, C2H5) and CH3? C(OR)?NH · HCl under elimination of ether or from 1,3-benzazaphospholines after oxidation or thermal treatment. Whereas the 1,3-benzazaphospholes don't react with acetyl chloride or methyl iodide the N-acetyl- and P-methyl-1,3-benzazaphospholes are formed starting with the ambident anion. Further reactions of the 1,3-benzazaphospholes and the nmr data of the compounds prepared are discussed. 相似文献
264.
Transient isotachophoresis-capillary zone electrophoresis with artificial seawater as the background electrolyte (BGE) was improved to further lower the limit of detection (LOD) for determination of nitrite and nitrate in seawater. By lowering the pH of BGE, the difference between effective mobility of nitrite and that of nitrate increased, thereby permitting increased sample volumes to be tolerated and their LOD values to decrease. Artificial seawater with pH adjusted to 3.0 using phosphate buffer was adopted as the BGE. To reverse electroosmotic flow (EOF), a capillary was flushed with 0.1 mM dilauryldimethylammonium bromide for 3 min before the capillary was filled with the BGE. Limits of detection (LODs) for nitrite and nitrate were 2.7 and 3.0 microg/l (as nitrogen), respectively. The LODs were obtained at a signal-to-noise ratio of 3. Values of the relative standard deviation (RSD) of peak area for these ions were 2.0 and 0.75%, respectively, when nitrite concentration was 0.05 mg/l and that of nitrate was 0.5 mg/l. The RSDs of peak height were 4.4 and 2.3%. The RSD values of migration time for these ions were 0.19 and 0.17%. The proposed method was applied to determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS-1, distributed by the National Research Council of Canada. Results agreed with the assigned tolerance interval. This method was also applied to determination of these ions in seawater collected around Osaka Bay. Results nearly agreed with those obtained by a conventional spectrophotometric method. 相似文献
265.
Irving Kuntz Doris M. Cheng A. H. Dekmezian Chang S. Hsu 《Journal of polymer science. Part A, Polymer chemistry》1987,25(11):3127-3141
Isobutylene has been polymerized in a continuous stirred tank reactor using a catalyst system comprised of 1-bromoadamantane and diethylaluminum chloride. The polymerization was carried out in hexane solvent at ?15 to ?27°C and gave 100% conversion to polyisobutylene (PIB) of 1000–3000 Mw. The results of pyrolysis–gas chromatography–mass spectrometry analyses are consistent with a mechanism involving the formation of the adamantyl cabocation and its addition to an isobutylene molecule to initiate polymerization. 13C-NMR analyses show that the PIB products contain R2C? CR2 and R2C? CHR olefin types. Information on the nature of these olefins and the route to their formation has been developed. 相似文献
266.
D?rte M. Vollmer R. Thier Hermann M. Bolt 《Fresenius' Journal of Analytical Chemistry》1998,362(3):324-328
A new method has been developed for the quantification of 2-hydroxyethylated cysteine resulting as adduct in blood proteins
after human exposure to ethylene oxide, by reversed-phase HPLC with fluorometric detection. The specific adduct is analysed
in albumin and in globin. After isolation of albumin and globin from blood, acid hydrolysis of the protein and precolumn derivatisation
of the digest with 9-fluorenylmethoxycarbonylchloride, the levels of derivatised S-hydroxyethylcysteine are analysed by RP-HPLC
and fluorescence detection, with a detection limit of 8 nmol/g protein. Background levels of S-hydroxyethylcysteine were quantified
in both albumin and globin, under special consideration of the glutathione transferase GSTT1 and GSTM1 polymorphisms. GSTT1
polymorphism had a marked influence on the physiological background alkylation of cysteine. While S-hydroxyethylcysteine levels
in “non-conjugators” were between 15 and 50 nmol/g albumin, “low conjugators” displayed levels between 8 and 21 nmol/g albumin,
and “high conjugators” did not show levels above the detection limit. The human GSTM1 polymorphism had no apparent effect
on background levels of blood protein 2-hydroxyethylation.
Received: 16 February 1998 / Revised: 27 March 1998 / Accepted: 1 April 1998 相似文献
267.
268.
Electrodes modified layer-by-layer by self-assembly of redox active polyelectrolytes comprised of osmium bipyridine-pyridine derivatized poly(allyl-amine) and poly(vinyl) sulfonate have been studied by EQCM, ellipsometry, cyclic voltammetry and electrochemical impedance spectroscopy in aqueous solutions of different anions and cations. Redox driven swelling by solvent exchange during oxidation, in excess to the hydration number, occurs by perturbation of the equilibrium between the osmotic and elastic forces as a result of the electrochemical injection of charge into the film. The exchanged mass and volume change during redox switching strongly depends on the nature of the anion under anion Donnan permselectivity conditions. 相似文献
269.
Amyloglucosidase, pullulanase, and glucose isomerase were coimmobilized onto granular chicken bone (BIOBONETM). Enzyme ratios showing optimum glucose and fructose production (0.7:10:22.3 U amyloglucosidase: pullulanase: glucose isomerase) resulted in 14.4±1.9% of activity bound relative to an equal amount of free enzyme. The estimated specific activity for these enzymes decreased 4.6-fold with immobilization. ReactionpH strongly influenced the yield and ratio of glucose and fructose produced. Net hexose production from the immobilized system was optimal atpH 6.5 and 55°C with a fructose yield of about 20%. 相似文献
270.