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881.
882.
883.
Reversing the Stereoselectivity of a Palladium‐Catalyzed O‐Glycosylation through an Inner‐Sphere or Outer‐Sphere Pathway
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Shaohua Xiang Kim Le Mai Hoang Jingxi He Yu Jia Tan Prof. Dr. Xue‐Wei Liu 《Angewandte Chemie (International ed. in English)》2015,54(2):604-607
An efficient and concise method for the construction of various O‐glycosidic bonds by a palladium‐catalyzed reaction with a 3‐O‐picoloyl glucal has been developed. The stereochemistry of the anomeric center derives from either an inner‐sphere or outer‐sphere pathway. Harder nucleophiles, such as aliphatic alcohols and sodium phenoxides give β‐products, and α products result from using softer nucleophiles, such as phenol. 相似文献
884.
Integrative Chemical Biology Approaches for Identification and Characterization of “Erasers” for Fatty‐Acid‐Acylated Lysine Residues within Proteins
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Zheng Liu Tangpo Yang Xin Li Tao Peng Prof. Howard C. Hang Prof. Xiang David Li 《Angewandte Chemie (International ed. in English)》2015,54(4):1149-1152
Acylation of proteins with fatty acids is important for the regulation of membrane association, trafficking, subcellular localization, and activity of many cellular proteins. While significant progress has been made in our understanding of the two major forms of protein acylation with fatty acids, N‐myristoylation and S‐palmitoylation, studies of the acylation of lysine residues, within proteins, with fatty acids have lagged behind. Demonstrated here is the use of integrative chemical biology approaches to examine human sirtuins as de‐fatty‐acid acylases in vitro and in cells. Photo‐crosslinking chemistry is used to investigate enzymes which recognize fatty‐acid acylated lysine. Human Sirt2 was identified as a robust lysine de‐fatty‐acid acylase in vitro. The results also show that Sirt2 can regulate the acylation of lysine residues, of proteins, with fatty acids within cells. 相似文献
885.
Tuning the Reactivity of Isocyano Group: Synthesis of Imidazoles and Imidazoliums from Propargylamines and Isonitriles in the Presence of Multiple Catalysts
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Dr. Shuo Tong Dr. Qian Wang Prof. Dr. Mei‐Xiang Wang Prof. Dr. Jieping Zhu 《Angewandte Chemie (International ed. in English)》2015,54(4):1293-1297
The reaction of propargyl amines with tert‐butylisonitrile in the presence of a catalytic amount of both Yb(OTf)3 and AgOTf afforded imidazoles, whereas the same reaction with primary and secondary alkylisonitriles, as well as arylisonitriles, in the presence of three metal salts [Yb(OTf)3/AgOTf/KOTf] resulted in the 1,3,4,5‐tetrasubstituted imidazoliums in excellent yields. Both chiral amines and chiral isonitriles can be used to provide corresponding chiral heterocycles without racemization. In this multiple catalytic system, Yb(OTf)3 catalyzed the insertion of isonitriles to the N? H bond of amines, AgOTf catalyzed the 5‐exo‐dig cyclization of the resulting amidine nitrogen to the tethered triple bond, and KOTf promoted the salt metathesis, thus providing at the same time the counterion to the imidazolium. Against common knowledge, the isocyano group acted in these reactions as a polarized triple bond instead of conventional carbene‐like function. 相似文献
886.
Determination of diflubenzuron and chlorbenzuron in fruits by combining acetonitrile‐based extraction with dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography
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In this study, a simple and low‐organic‐solvent‐consuming method combining an acetonitrile‐partitioning extraction procedure followed by “quick, easy, cheap, effective, rugged and safe” cleanup with ionic‐liquid‐based dispersive liquid–liquid microextraction and high‐performance liquid chromatography with diode array detection was developed for the determination of diflubenzuron and chlorbenzuron in grapes and pears. Ionic‐liquid‐based dispersive liquid–liquid microextraction was performed using the ionic liquid 1‐hexyl‐3‐methylimidazolium hexafluorophosphate as the extractive solvent and acetonitrile extract as the dispersive solvent. The main factors influencing the efficiency of the dispersive liquid–liquid microextraction were evaluated, including the extractive solvent type and volume and the dispersive solvent volume. The validation parameters indicated the suitability of the method for routine analyses of benzoylurea insecticides in a large number of samples. The relative recoveries at three spiked levels ranged between 98.6 and 109.3% with relative standard deviations of less than 5.2%. The limit of detection was 0.005 mg/kg for the two insecticides. The proposed method was successfully used for the rapid determination of diflubenzuron and chlorbenzuron residues in real fruit samples. 相似文献
887.
Development of a liquid chromatography with mass spectrometry method for the determination of gelsemine in rat plasma and tissue: Application to a pharmacokinetic and tissue distribution study
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Shuangshuang Zhang Shuping Hu Xiangxiang Yang Jiaqi Shen Xiaoyong Zheng Kexin Huang Zheng Xiang 《Journal of separation science》2015,38(6):936-942
Gelsemine from Gelsemium elegans Benth is a potential anesthetic and analgesic agent with no physical dependence and opiate addiction. This study was aimed at developing an ultrafast liquid chromatography coupled to tandem mass spectrometry method to quantify gelsemine in rat plasma and tissues. Plasma and tissues were processed with acetonitrile precipitation, and dendrobine was chosen as the internal standard. Sample separation was performed on an ACQUITY HSS T3 column. The mobile phase consisted of acetonitrile and 0.1% formic acid aqueous solution. Multiple reactions monitoring mode was utilized to detect the compounds of interest. The mass spectrometer was operated in the positive ion mode for detection. The MS/MS ion transitions monitored were m/z 323.2→70.5 for gelsemine and 264.2→108.05 for dendrobine, respectively. The calibration curves were linear over the range of 1–500 ng/mL in all biological matrices. The lower limit of quantification for rats plasma and tissues was 1.0 ng/mL. The values for inter‐ and intraday precision and accuracy were well within the ranges acceptable (< 15%). It was successfully applied to the pharmacokinetic and tissue distribution studies of gelsemine after intravenous doses of 5, 2, and 0.5 mg/kg in rats. These data of gelsemine would be useful for clinical application and further development. 相似文献
888.
Separation and purification of five alkaloids from Aconitum duclouxii by counter‐current chromatography
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Yarong Wang Shining Cai Yang Chen Xumei Zhou Jia Liu Xin Xu Qiang Xia Mao Lin Jili Zhang Weili Huang Wenjun Wang Canhui Xiang Guozhen Cui Lianfeng Du Huan He Baohui Qi 《Journal of separation science》2015,38(13):2320-2326
C19‐diterpenoid alkaloids are the main components of Aconitum duclouxii Levl. The process of separation and purification of these compounds in previous studies was tedious and time consuming, requiring multiple chromatographic steps, thus resulted in low recovery and high cost. In the present work, five C19‐diterpenoid alkaloids, namely, benzoylaconine ( 1 ), N‐deethylaconitine ( 2 ), aconitine ( 3 ), deoxyaconitine ( 4 ), and ducloudine A ( 5 ), were efficiently prepared from A. duclouxii Levl (Aconitum L.) by ethyl acetate extraction followed with counter‐current chromatography. In the process of separation, the critical conditions of counter‐current chromatography were optimized. The two‐phase solvent system composed of n‐hexane/ethyl acetate/methanol/water/NH3·H2O (25%) (1:1:1:1:0.1, v/v) was selected and 148.2 mg of 1 , 24.1 mg of 2 , 250.6 mg of 3 , 73.9 mg of 4, and 31.4 mg of 5 were obtained from 1 g total Aconitum alkaloids extract, respectively, in a single run within 4 h. Their purities were found to be 98.4, 97.2, 98.2, 96.8, and 96.6%, respectively, by ultra‐high performance liquid chromatography analysis. The presented separation and purification method was simple, fast, and efficient, and the obtained highly pure alkaloids are suitable for biochemical and toxicological investigation. 相似文献
889.
Wei Shi Jian‐Jun Liu Xiang‐Ping Ou Chang‐Cang Huang 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(4):289-293
A homochiral helical three‐dimensional coordination polymer, poly[[(μ2‐acetato‐κ3O,O′:O)(hydroxido‐κO)(μ4‐5‐nicotinamido‐1H‐1,2,3,4‐tetrazol‐1‐ido‐κ5N1,O:N2:N4:N5)(μ3‐5‐nicotinamido‐1H‐1,2,3,4‐tetrazol‐1‐ido‐κ4N1,O:N2:N4:N5)dicadmium(II)] 0.75‐hydrate], {[Cd2(C7H5N6O)2(CH3COO)(OH)]·0.75H2O}n, was synthesized by the reaction of cadmium acetate, N‐(1H‐tetrazol‐5‐yl)isonicotinamide (H‐NTIA), ethanol and H2O under hydrothermal conditions. The asymmetric unit contains two crystallographically independent CdII cations, two deprotonated 5‐nicotinamido‐1H‐1,2,3,4‐tetrazol‐1‐ide (NTIA−) ligands, one acetate anion, one hydroxide anion and three independent partially occupied water sites. The two CdII cations, with six‐coordinated octahedral and seven‐coordinated pentagonal bipyramidal geometries are located on general sites. The tetrazole group of one symmetry‐independent NTIA− ligand links one of the independent CdII cations into 61 helical chains, while the other NTIA− ligand links the other independent CdII cations into similar but unequal 61 helical chains. These chains, with a pitch of 24.937 (5) Å, intertwine into a double‐stranded helix. Each of the double‐stranded 61 helices is further connected to six adjacent helical chains through an acetate μ2‐O atom and the tetrazole group of the NTIA− ligand into a three‐dimensional framework. The helical channel is occupied by the isonicotinamide groups of NTIA− ligands and two helices are connected to each other through the pyridine N and carbonyl O atoms of isonicotinamide groups. In addition, N—H...O and O—H...N hydrogen bonds exist in the complex. 相似文献
890.
Qiu‐Ying Huang Ming‐Yang Su Xiang‐Ru Meng 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(6):474-478
The combination of N‐heterocyclic and multicarboxylate ligands is a good choice for the construction of metal–organic frameworks. In the title coordination polymer, poly[bis{μ2‐1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole‐κ2N3:N4}(μ4‐butanedioato‐κ4O1:O1′:O4:O4′)(μ2‐butanedioato‐κ2O1:O4)dicadmium], [Cd(C4H4O4)(C9H8N6)]n, each CdII ion exhibits an irregular octahedral CdO4N2 coordination geometry and is coordinated by four O atoms from three carboxylate groups of three succinate (butanedioate) ligands and two N atoms from two 1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole (bimt) ligands. CdII ions are connected by two kinds of crystallographically independent succinate ligands to generate a two‐dimensional layered structure with bimt ligands located on each side of the layer. Adjacent layers are further connected by hydrogen bonding, leading to a three‐dimensional supramolecular architecture in the solid state. Thermogravimetric analysis of the title polymer shows that it is stable up to 529 K and then loses weight from 529 to 918 K, corresponding to the decomposition of the bimt ligands and succinate groups. The polymer exhibits a strong fluorescence emission in the solid state at room temperature. 相似文献