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991.
992.
993.
Mattea Carmen Castrovilli Paola Bolognesi Antonella Cartoni Daniele Catone Patrick O’Keeffe Anna Rita Casavola Stefano Turchini Nicola Zema Lorenzo Avaldi 《Journal of the American Society for Mass Spectrometry》2014,25(3):351-367
In the present work, we studied the photoinduced ion chemistry of the halogenated pyrimidines, a class of prototype radiosensitizing molecules, in the energy region 9–15 eV. The work was stimulated by previous studies on inner shell site-selective fragmentation of the pyrimidine molecule, which have shown that the fragmentation is governed by the population/formation of specific ionic states with a hole in valence orbitals, which in turn correlate to accessible dissociation limits. The combined experimental and theoretical study of the appearance energies of the main fragments provides information on the geometric structure of the products and on the role played by the specific halogen atom and the site of halogenation in the dissociation process. This information can be used to gain new insights on the elementary mechanisms that could possibly explain the enhanced radiation damage to the DNA bases or to the medium in which the bases are embedded, thereby contributing to their radiosensitizing effect. Figure
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994.
Ventrella Andrea Verrone Raffaella Cosma Pinalysa Fini Paola Longobardi Francesco Lippolis Vincenzo Pascale Michelangelo Catucci Lucia 《Journal of solution chemistry》2014,43(8):1436-1447
Journal of Solution Chemistry - The interaction of ochratoxin A (OTA) with heptakis-2,6-di-O-methyl-β-cyclodextrin (DIMEB) in aqueous solutions at two different pHs (3.5 and 9.5) was studied... 相似文献
995.
Anna Barattucci Paola Bonaccorsi Teresa Papalia Nadia Manganaro Giuseppe Gattuso 《Tetrahedron letters》2014
meso-(R,S)-Dithia[3.3]-paracyclophane S,S′-dioxide is formed with complete stereoselection by the thermolysis of 3,3′-[1,4-phenylene-bis(methylenesulfinyl)]-dipropanoate—that generates in situ two transient sulfenic acid functions—in the presence of p-diethynylbenzene. By employing an improved procedure that we have recently optimized, the title compound has been prepared in a 70% yield as a single diastereoisomer. A density functional B3LYP/6-311+G(d,p) study demonstrates that the final syn-addition cyclization step takes place under kinetic control, through a five-membered transition state that defines the stereochemistry of the resulting cyclophane. 相似文献
996.
Aura Tintaru Christophe Chendo Qi Wang Stéphane Viel Gilles Quéléver Ling Peng Paola Posocco Sabrina Pricl Laurence Charles 《Analytica chimica acta》2014
Tandem mass spectrometry and ion mobility spectrometry experiments were performed on multiply charged molecules formed upon conjugation of a poly(amidoamine) (PAMAM) dendrimer with a poly(ethylene oxide) (PEO) linear polymer to evidence any conformational modification as a function of their charge state (2+ to 4+) and of the adducted cation (H+vs Li+). Experimental findings were rationalized by molecular dynamics simulations. The G0 PAMAM head-group could accommodate up to three protons, with protonated terminal amine group enclosed in a pseudo 18-crown-6 ring formed by the PEO segment. This particular conformation enabled a hydrogen bond network which allowed long-range proton transfer to occur during collisionally activated dissociation. In contrast, lithium adduction was found to mainly occur onto oxygen atoms of the polyether, each Li+ cation being coordinated by a 12-crown-4 pseudo structure. As a result, for the studied polymeric segment (Mn = 1500 g mol−1), PEO-PAMAM hybrid molecules exhibited a more expanded shape when adducted to lithium as compared to proton. 相似文献
997.
Unexpected Anion Effect in the Alkoxylation of Alkynes Catalyzed by N‐Heterocyclic Carbene (NHC) Cationic Gold Complexes 下载免费PDF全文
Luca Biasiolo Marina Trinchillo Prof. Paola Belanzoni Dr. Leonardo Belpassi Prof. Dr. Vincenzo Busico Dr. Gianluca Ciancaleoni Dr. Angela D'Amora Prof. Alceo Macchioni Prof. Francesco Tarantelli Dr. Daniele Zuccaccia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14594-14598
The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N‐heterocyclic carbene‐based gold catalyst, [(NHC)AuX] (X=BARF?, BF4?, OTf?, OTs?, TFA?, or OAc?) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs? anion provides the best compromise to achieve efficient catalysis. 相似文献
998.
Towards the Fabrication of the Top‐Contact Electrode in Molecular Junctions by Photoreduction of a Metal Precursor 下载免费PDF全文
Dr. Santiago Martín Dr. Gorka Pera Dr. Luz M. Ballesteros Adam J. Hope Santiago Marqués‐González Prof. Paul J. Low Prof. Francesc Pérez‐Murano Prof. Richard J. Nichols Dr. Pilar Cea 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(12):3421-3426
Langmuir films of 4‐{[4‐({4‐[(trimethylsilyl)ethynyl]phenyl}ethynyl)phenyl]ethynyl} benzenaminium chloride ([ 1 H ]Cl) undergo anion metathesis when assembled on an aqueous auric acid (HAuCl4) subphase. Subsequent transfer to solid supports gives well‐formed Langmuir–Blodgett (LB) monolayers of [ 1 H ]AuCl4 in which the trimethylsilyl group serves as the surface contacting group. Photoreduction of the aurate on these monolayers leads to the formation of metallic gold nanoislands, which were distributed over the surface of the film. Electrical properties of these nascent devices were determined by recording current–voltage (I–V) curves with conductive atomic force microscopy (c‐AFM) using the PeakForce tunneling AFM (PF‐TUNA) mode. This gives consistent sigmoidal I–V curves that are indicative of well‐behaved junctions free of metallic filaments and short circuits. The photoreduction of a metal precursor incorporated onto monomolecular films is therefore proposed as an effective method for the fabrication of molecular junctions. 相似文献
999.
Dr. Paola Riente Alba Matas Adams Dr. Josep Albero Prof. Emilio Palomares Prof. Miquel A. Pericàs 《Angewandte Chemie (International ed. in English)》2014,53(36):9613-9616
The development of enantioselective catalytic processes that make use of sunlight as the energy source and nontoxic, affordable materials as catalysts represents one of the new and rapidly evolving areas in chemical research. The direct asymmetric α‐alkylation of aldehydes with α‐bromocarbonyl compounds can be successfully achieved by combining bismuth‐based materials as low‐band‐gap photocatalysts with the second‐generation MacMillan imidazolidinone as the chiral catalyst and simulated sunlight as a low‐cost and clean energy source. This reaction also proceeded with high efficiency when the reaction vial was exposed to the morning sunlight on a clear September day in Tarragona, Spain. 相似文献
1000.
Dr. Leandro M. C. Pinto Dr. Paola Quaino Dr. Elizabeth Santos Prof. Dr. Wolfgang Schmickler 《Chemphyschem》2014,15(1):132-138
The deposition of Cu2+ and Zn2+ from aqueous solution has been investigated by a combination of classical molecular dynamics, density functional theory, and a theory developed by the authors. For both cases, the reaction proceeds through two one‐electron steps. The monovalent ions can get close to the electrode surface without losing hydration energy, while the divalent ions, which have a stronger solvation sheath, cannot. The 4s orbital of Cu interacts strongly with the sp band and more weakly with the d band of the copper surface, while the Zn 4s orbital couples only to the sp band of Zn. At the equilibrium potential for the overall reaction, the energy of the intermediate Cu+ ion is only a little higher than that of the divalent ion, so that the first electron transfer can occur in an outer‐sphere mode. In contrast, the energy of the Zn+ ion lies too high for a simple outer‐sphere reaction to be favorable; in accord with experimental data this suggests that this step is affected by anions. 相似文献