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161.
162.
Enantioselective Synthesis of Vicinal All‐Carbon Quaternary Centers via Iridium‐Catalyzed Allylic Alkylation
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Dr. J. Caleb Hethcox Samantha E. Shockley Prof. Dr. Brian M. Stoltz 《Angewandte Chemie (International ed. in English)》2018,57(28):8664-8667
The development of the first enantioselective transition‐metal‐catalyzed allylic alkylation providing access to acyclic products bearing vicinal all‐carbon quaternary centers is disclosed. The iridium‐catalyzed allylic alkylation reaction proceeds with excellent yields and selectivities for a range of malononitrile‐derived nucleophiles and trisubstituted allylic electrophiles. The utility of these sterically congested products is explored through a series of diverse chemo‐ and diastereoselective product transformations to afford a number of highly valuable, densely functionalized building blocks, including those containing vicinal all‐carbon quaternary stereocenters. 相似文献
163.
Exploiting Synergistic Effects in Organozinc Chemistry for Direct Stereoselective C‐Glycosylation Reactions at Room Temperature
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Dr. Alberto Hernán‐Gómez Dr. Samantha A. Orr Dr. Marina Uzelac Dr. Alan R. Kennedy Dr. Santiago Barroso Dr. Xavier Jusseau Dr. Sébastien Lemaire Dr. Vittorio Farina Prof. Eva Hevia 《Angewandte Chemie (International ed. in English)》2018,57(33):10630-10634
Pairing a range of bis(aryl) zinc reagents ZnAr2 with the stronger Lewis acidic [(ZnArF2)] (ArF=C6F5), enables highly stereoselective cross‐coupling between glycosyl bromides and ZnAr2 without the use of a transition metal. Reactions occur at room temperature with excellent levels of stereoselectivity, where ZnArF2 acts as a non‐coupling partner although its presence is crucial for the execution of the C(sp2)–C(sp3) bond formation process. Mechanistic studies have uncovered a unique synergistic partnership between the two zinc reagents, which circumvents the need for transition‐metal catalysis or forcing reaction conditions. Key to the success of the coupling is the avoidance of solvents that act as Lewis bases versus diarylzinc compounds (e.g. THF). 相似文献
164.
The ratio of the Br + Br2 halogen atom exchange rate, k2, to the Br + HI reaction rate k1, has been determined experimentally by using an isotopically selective, laser-initiated chemical reaction. At 294 K, k2/k1 = 4, and thus, k2 = 4 × 10?11 cm3 molecule?1 s?1. 相似文献
165.
Judy N. Hart Laure Bourgeois Raoul Cervini Yi-Bing Cheng George P. Simon Leone Spiccia 《Journal of Sol-Gel Science and Technology》2007,42(2):107-117
TiO2 nanoparticles are widely used for many applications and an understanding of the crystallization behavior of TiO2 is essential, so that heat treatment conditions can be optimized for particular applications. The effect of sol–gel synthesis
conditions on the crystallization behavior of TiO2 has, therefore, been investigated. Complete crystallization to the anatase phase (determined by XRD and TEM analysis) was
achieved during drying of the synthesis product at 95 °C. The nanoparticles grew during heat treatment, reaching ∼10–15 nm
in diameter with a heat treatment at 450 °C. Explanations are offered for the observed differences in the crystallization
and particle growth behavior of TiO2 synthesized under various conditions. 相似文献
166.
The C2H2 + O(3P) and HCCO + O(3P) reactions are investigated using Fourier transform infrared (FTIR) emission spectroscopy. The O(3P) radicals are produced by 193 nm photolysis of an SO2 precursor or microwave discharge in O2. The HCCO radical is either formed in the first step of the C2H2 + O(3P) reaction or by 193 nm photodissociation of ethyl ethynyl ether. Vibrationally excited CO and CO2 products are observed. The microwave discharge experiment [C2H2 + O(3P)] shows a bimodal distribution of the CO(v) product, which is due to the sequential C2H2 + O(3P) and HCCO + O(3P) reactions. The vibrational distribution of CO(v) from the HCCO + O(3P) reaction also shows its own bimodal shape. The vibrational distribution of CO(v) from C2H2 + O(3P) can be characterized by a Boltzmann plot with a vibrational temperature of approximately 2400 +/- 100 K, in agreement with previous results. The CO distribution from the HCCO + O(3P) reaction, when studied under conditions to minimize other processes, shows very little contamination from other reactions, and the distribution can be characterized by a linear combination of Boltzmann plots with two vibrational temperatures: 2320 +/- 40 and 10 300 +/- 600 K. From the experimental results and previous theoretical work, the bimodal CO(v) distribution for the HCCO + O(3P) reaction suggests a sequential dissociation process of the HC(O)CO++ --> CO + HCO; HCO --> H + CO. 相似文献
167.
Gianluca Melillo Lorella Izzo Roberto Centore Angela Tuzi Alexander Z. Voskoboynikov Leone Oliva 《Journal of molecular catalysis. A, Chemical》2005,230(1-2):29-33
The meso ansa zirconocene with dimethylsilyl bridge, activated by methylalumoxane, catalyses the ethylene polymerization, producing ethyl-branched polyethylene. With respect to the polymers obtained with the previously investigated meso zirconocenes, we have found higher branching amount and lower molecular weight. The rapid β-H transfer from the growing chain to the coordinated monomer could account for both these features of the polymer. The investigation on the structural parameters of the complex, through X-ray diffraction analysis, and on the electrophilicity of the cationic center, through NMR experiments, suggests, as a possible rationalization of this behavior, the obstruction in the inward site. 相似文献
168.
R. Benedikt F. Ulzer Focke Finkener Th. Morawski Alfred H. Allen O. Schweissinger R. Marzahn Dieterich Hazura F. W. A. Woll Bruno Röse Ch. Dubois L. Padé R. Bensemann Audoynaud Levallois T. Leone A. Longi F. Benecke Joseph Herz P. Soltsien C. Schädler C. L. Reimer W. Will H. Hager 《Analytical and bioanalytical chemistry》1888,27(1):524-539
169.
Design of a Prussian Blue Analogue/Carbon Nanotube Thin‐Film Nanocomposite: Tailored Precursor Preparation,Synthesis, Characterization,and Application
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Samantha Husmann Prof. Aldo J. G. Zarbin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6643-6653
Multi‐walled carbon nanotubes (MWCNTs) filled with different species of cobalt (metallic cobalt, cobalt oxide) were synthesized by a chemical vapor deposition method through cobaltocene pyrolysis. A systematic study was performed to correlate different experimental conditions with the structure and characteristics of the obtained material. Thin films of Co‐filled CNTs were deposited over conductive substrates through a liquid–liquid interfacial method and were used for cobalt hexacyanoferrate (CoHCFe) electrodeposition by an innovative route in which the Co species encapsulated in the CNTs were employed as reactants. The CNT/CoHCFe films were characterized by different spectroscopic, microscopic, and electrochemical techniques and presented high electrochemical stability in different media. The nanocomposites were applied as both an electrochemical sensor to H2O2 and a cathode for ion batteries and showed limits of detection at approximately 3.7 nmol L ?1 and a capacity of 130 mAh g?1 at a current density of 5 A g?1. 相似文献
170.
Mingfeng Yu Ngee H Lim Samantha Ellis Hideaki Nagase James A Triccas Peter J Rutledge Matthew H Todd 《ChemistryOpen》2013,2(3):99-105
The synthesis and matrix metalloproteinase (MMP) inhibitory activity of a cyclam–marimastat conjugate and its metal complexes are described. The conjugate, synthesized with a copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition (“click” reaction), contains two zinc-binding groups (ZBGs). The metal complexation behavior with copper(II) and zinc(II) was investigated using UV/Vis spectrophotometry and 1H NMR spectroscopy, respectively, demonstrating that the first equivalent of the metal ion was chelated by the cyclam-triazole moiety rather than the hydroxamic acid site. Thus, the corresponding mononuclear metal–cyclam complexes were successfully prepared with one equivalent of the metal salt. Both the cyclam–marimastat conjugate and its metal complexes exhibited slightly reduced potency against MMP-1, but essentially identical inhibitory activity against MMP-3. The conjugate and its metal complexes displayed little or no cytotoxicity, further supporting their potential suitability for imaging MMP localization and activity. To the best of our knowledge, this is the first report that describes the incorporation of metal complexes into an MMP inhibitor without influencing the preexisting ZBG, and the first report of the evaluation of structures containing more than one ZBG as MMP inhibitors. 相似文献